Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
20 pages, 5947 KiB  
Article
Se-MAG Is a Convenient Additive for Experimental Phasing and Structure Determination of Membrane Proteins Crystallised by the Lipid Cubic Phase (In Meso) Method
by Coilín Boland, Chia-Ying Huang, Shiva Shanker Kaki, Meitian Wang, Vincent Olieric and Martin Caffrey
Crystals 2023, 13(9), 1402; https://doi.org/10.3390/cryst13091402 - 21 Sep 2023
Viewed by 824
Abstract
Both intensity and phase information are needed for structure determination by macromolecular X-ray crystallography. The diffraction experiment provides intensities. Phases must be accessed indirectly by molecular replacement, or by experimental phasing. A popular method for crystallising membrane proteins employs a lipid cubic mesophase [...] Read more.
Both intensity and phase information are needed for structure determination by macromolecular X-ray crystallography. The diffraction experiment provides intensities. Phases must be accessed indirectly by molecular replacement, or by experimental phasing. A popular method for crystallising membrane proteins employs a lipid cubic mesophase (the in meso method). Monoolein is the most popular lipid for in meso crystallisation. Invariably, the lipid co-crystallises with the protein recapitulating the biomembrane from whence it came. We reasoned that such a lipid bearing a heavy atom could be used for experimental phasing. In this study, we replaced half the monoolein in the mesophase with a seleno-labelled analogue (Se-MAG), which has a selenium atom in the fatty acyl chain of the lipid. The lipid mixture formed the cubic mesophase and grew crystals by the in meso method of the alginate transporter, AlgE, and the lipoprotein N-acyltransferase, Lnt. Se-MAGs co-crystallised with both proteins and were used to obtain phases for high-resolution structure determination by the selenium single-wavelength anomalous diffraction method. The use of such a mixed lipid system may prove to be a general strategy for the experimental phasing part of crystallographic structure determination of membrane proteins that crystallise via the in meso method. Full article
(This article belongs to the Special Issue Membrane Protein Crystallography)
Show Figures

Figure 1

12 pages, 4211 KiB  
Article
Human Eye Contrast Sensitivity to Vehicle Displays under Strong Ambient Light
by Yizhou Qian, Zhiyong Yang, En-Lin Hsiang, Qian Yang, Kevin Nilsen, Yu-Hsin Huang, Kuan-Heng Lin and Shin-Tson Wu
Crystals 2023, 13(9), 1384; https://doi.org/10.3390/cryst13091384 - 18 Sep 2023
Viewed by 1265
Abstract
Vehicle displays are becoming more integrated into our daily lives. Achieving a premium driving experience demands the display panel to have high-resolution density and sufficient brightness, particularly when exposed to intense ambient light, as direct sunlight can obscure the displayed images. Combining Barten’s [...] Read more.
Vehicle displays are becoming more integrated into our daily lives. Achieving a premium driving experience demands the display panel to have high-resolution density and sufficient brightness, particularly when exposed to intense ambient light, as direct sunlight can obscure the displayed images. Combining Barten’s model and diffraction theory, the performance of both infotainment displays and head-up displays (HUDs) is evaluated. For infotainment displays, over 800 nit brightness is essential for the driver to discern 55 pixel-per-degree (PPD) patterns under direct sunlight. For HUDs, a delicate balance between resolution density, brightness, transparency, and image quality must be exercised. By slightly reducing the resolution density to 50 PPD, the transparent micro-LED panel can concurrently achieve a reduced background image blur, low required display brightness (~4000 nits), and high background transmittance (~90%). Full article
(This article belongs to the Section Liquid Crystals)
Show Figures

Figure 1

20 pages, 3861 KiB  
Article
Systematic Assessment of Phonon and Optical Characteristics for Gas-Source Molecular Beam Epitaxy-Grown InP1−xSbx/n-InAs Epifilms
by Devki N. Talwar and Hao-Hsiung Lin
Crystals 2023, 13(9), 1367; https://doi.org/10.3390/cryst13091367 - 11 Sep 2023
Viewed by 698
Abstract
Experimental and theoretical assessments of phonon and optical characteristics are methodically accomplished for comprehending the vibrational, structural, and electronic behavior of InP1−xSbx/n-InAs samples grown by Gas-Source Molecular Beam Epitaxy. While the polarization-dependent Raman scattering measurements revealed InP-like doublet covering [...] Read more.
Experimental and theoretical assessments of phonon and optical characteristics are methodically accomplished for comprehending the vibrational, structural, and electronic behavior of InP1−xSbx/n-InAs samples grown by Gas-Source Molecular Beam Epitaxy. While the polarization-dependent Raman scattering measurements revealed InP-like doublet covering optical modes (ωLOInP~350 cm−1, ωTOInP~304 cm−1) and phonons activated by disorders and impurities, a single unresolved InSb-like broadband is detected near ~195 cm−1. In InP1−xSbx, although no local vibrational (InSb:P; x → 1) and gap modes (InP:Sb; x → 0) are observed, the Raman line shapes exhibited large separation between the optical phonons of its binary counterparts, showing features similar to the phonon density of states, confirming “two-mode-behavior”. Despite the earlier suggestions of large miscibility gaps in InP1−xSbx epilayers for x between 0.02 and 0.97, our photoluminescence (PL) results of energy gaps insinuated achieving high-quality single-phase epilayers with x ~ 0.3 in the miscibility gap. Complete sets of model dielectric functions (MDFs) are obtained for simulating the optical constants of binary InP, InSb, and ternary InP1−xSbx alloys in the photon energy (0 ≤ E ≤ 6 eV) region. Detailed MDF analyses of refractive indices, extinction coefficients, absorption and reflectance spectra have exhibited results in good agreement with the spectroscopic ellipsometry data. For InP0.67Sb0.33 alloy, our calculated lowest energy bandgap E0 ~ 0.46 eV has validated the existing first-principles calculation and PL data. We feel that our results on Raman scattering, PL measurements, and simulations of optical constants provide valuable information for the vibrational and optical traits of InP1−xSbx/n-InAs epilayers and can be extended to many other technologically important materials. Full article
(This article belongs to the Special Issue Epitaxial Growth of Semiconductor Materials and Devices)
Show Figures

Figure 1

16 pages, 11095 KiB  
Article
Nanocrystallization of Cu46Zr33.5Hf13.5Al7 Metallic Glass
by Jaskaran S. Saini, Tamara D. Koledin, Tittaya Thaiyanurak, Lei Chen, Melissa K. Santala and Donghua Xu
Crystals 2023, 13(9), 1322; https://doi.org/10.3390/cryst13091322 - 29 Aug 2023
Viewed by 1499
Abstract
The recently discovered Cu46Zr33.5Hf13.5Al7 (at.%) bulk metallic glass (BMG) presents the highest glass-forming ability (GFA) among all known copper-based alloys, with a record-breaking critical casting thickness (or diameter) of 28.5 mm. At present, much remains to [...] Read more.
The recently discovered Cu46Zr33.5Hf13.5Al7 (at.%) bulk metallic glass (BMG) presents the highest glass-forming ability (GFA) among all known copper-based alloys, with a record-breaking critical casting thickness (or diameter) of 28.5 mm. At present, much remains to be explored about this new BMG that holds exceptional promise for engineering applications. Here, we report our study on the crystallization behavior of this new BMG, using isochronal and isothermal differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). With the calorimetric data, we determine the apparent activation energy of crystallization, the Avrami exponent, and the lower branch of the isothermal time–temperature–transformation (TTT) diagram. With XRD and TEM, we identify primary and secondary crystal phases utilizing samples crystallized to different degrees within the calorimeter. We also estimate the number density, nucleation rate, and growth rate of the primary crystals through TEM image analysis. Our results reveal that the crystallization in this BMG has a high activation energy of ≈360 kJ/mole and that the primary crystallization of this BMG produces a high number density (≈1021 m−3 at 475 °C) of slowly growing (growth rate < 0.5 nm/s at 475 °C) Cu10(Zr,Hf)7 nanocrystals dispersed in the glassy matrix, while the second crystallization event further produces a new phase, Cu(Zr,Hf)2. The results help us to understand the GFA and thermal stability of this new BMG and provide important guidance for its future engineering applications, including its usage as a precursor to glass–crystal composite or bulk nanocrystalline structures. Full article
(This article belongs to the Special Issue Aggregation, Nucleation and Crystallization)
Show Figures

Figure 1

17 pages, 13668 KiB  
Review
Imidazol(in)ium-2-Thiocarboxylate Zwitterion Ligands: Structural Aspects in Coordination Complexes
by David Elorriaga, Blanca Parra-Cadenas, Paula Pérez-Ramos, Raquel G. Soengas, Fernando Carrillo-Hermosilla and Humberto Rodríguez-Solla
Crystals 2023, 13(9), 1304; https://doi.org/10.3390/cryst13091304 - 26 Aug 2023
Viewed by 1373
Abstract
Azolium-2-thiocarboxylate zwitterion ligands have emerged as a promising class of compounds in the field of coordination chemistry due to their unique structural features and versatile applications. These ligands are characterized by a positively charged azolium ring and a negatively charged thiocarboxylate moiety, making [...] Read more.
Azolium-2-thiocarboxylate zwitterion ligands have emerged as a promising class of compounds in the field of coordination chemistry due to their unique structural features and versatile applications. These ligands are characterized by a positively charged azolium ring and a negatively charged thiocarboxylate moiety, making them capable of forming stable coordination complexes with various metal ions. One of the key structural aspects that make these ligands attractive for coordination chemistry is their ability to adopt diverse coordination modes with metal centers. The nature of these ligands enables them to engage in both monodentate and bidentate coordination, resulting in the formation of chelated complexes with enhanced stability and controlled geometry or the formation of polynuclear structures. This versatility in coordination behavior allows for the design of tailored ligands with specific metal-binding preferences, enabling the creation of unique and finely tuned coordination architectures. The azolium-2-thiocarboxylate zwitterionic ligands offer a promising platform for the design of coordination complexes with diverse structural architectures. Full article
Show Figures

Figure 1

9 pages, 12037 KiB  
Article
Cortesognoite, CaV2Si2O7(OH)2·H2O, a New Mineral from the Molinello Manganese Mine, Graveglia Valley, Italy
by Chi Ma, Cristina Carbone and Donato Belmonte
Crystals 2023, 13(9), 1295; https://doi.org/10.3390/cryst13091295 - 23 Aug 2023
Viewed by 1090
Abstract
Cortesognoite (IMA 2014-029), CaV2Si2O7(OH)2·H2O, is a new vanadium silicate mineral that occurs within V-bearing lawsonite in association with vanadiocarpholite, chalcocite, quartz, minor poppiite, roscoelite, vanadomalayaite and volborthite in a silicified wood hosted in [...] Read more.
Cortesognoite (IMA 2014-029), CaV2Si2O7(OH)2·H2O, is a new vanadium silicate mineral that occurs within V-bearing lawsonite in association with vanadiocarpholite, chalcocite, quartz, minor poppiite, roscoelite, vanadomalayaite and volborthite in a silicified wood hosted in Mn-ore-bearing metacherts from the Molinello manganese mine in the Graveglia Valley, Northern Apennines, Liguria, Italy. The mean chemical composition of type cortesognoite by electron probe microanalysis is (wt%) SiO2 34.33, V2O3 31.38, CaO 15.80, Al2O3 7.69, MnO 0.14, FeO 0.09, MgO 0.06, TiO2 0.02 and H2O 10.29, totaling 99.80, giving rise to an empirical formula of (Ca0.99Mn0.01)(V1.47Al0.53Mg0.01)Si2.00O7(OH)2·H2O. The end-member formula is CaV2Si2O7(OH)2·H2O. Cortesognoite has the Cmcm lawsonite structure with a = 5.85(1) Å, b = 8.79(1) Å, c = 13.13(1) Å, V = 675(1) Å3 and Z = 4 as revealed by electron back-scatter diffraction. The calculated density using the measured composition is 3.44 g/cm3. Cortesognoite is a secondary alteration phase, formed with V-bearing lawsonite by multi-stage hydrothermal processes that occurred in the silicified fossil wood. The mineral name is in honor of Luciano Cortesogno, professor of petrography at University of Genova, Italy. Full article
(This article belongs to the Special Issue The Progress of In-Situ Study of Mineralogy and Gemmology)
Show Figures

Figure 1

35 pages, 6836 KiB  
Article
An Operando Study of the Thermal Reduction of BaTiO3 Crystals: The Nature of the Insulator–Metal Transition of the Surface Layer
by Christian Rodenbücher, Gustav Bihlmayer, Carsten Korte, Daniel Rytz, Jacek Szade and Kristof Szot
Crystals 2023, 13(8), 1278; https://doi.org/10.3390/cryst13081278 - 19 Aug 2023
Cited by 2 | Viewed by 1099
Abstract
The insulator-to-metal transition upon the thermal reduction of perovskites is a well-known yet not completely understood phenomenon. By combining different surface-sensitive analysis techniques, we analyze the electronic transport properties, electronic structure, and chemical composition during the annealing and cooling of high-quality BaTiO3 [...] Read more.
The insulator-to-metal transition upon the thermal reduction of perovskites is a well-known yet not completely understood phenomenon. By combining different surface-sensitive analysis techniques, we analyze the electronic transport properties, electronic structure, and chemical composition during the annealing and cooling of high-quality BaTiO3 single crystals under ultra-high-vacuum conditions. Our results reveal that dislocations in the surface layer of the crystal play a decisive role as they serve as easy reduction sites. In this way, conducting filaments evolve and allow for turning a macroscopic crystal into a state of metallic conductivity upon reduction, although only an extremely small amount of oxygen is released. After annealing at high temperatures, a valence change of the Ti ions in the surface layer occurs, which becomes pronounced upon the quenching of the crystal. This shows that the reduction-induced insulator-to-metal transition is a highly dynamic non-equilibrium process in which resegregation effects in the surface layer take place. Upon cooling to the ferroelectric phase, the metallicity can be preserved, creating a “ferroelectric metal.” Through a nanoscale analysis of the local conductivity and piezoelectricity, we submit that this phenomenon is not a bulk effect but originates from the simultaneous existence of dislocation-based metallic filaments and piezoelectrically active areas, which are spatially separated. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
Show Figures

Figure 1

16 pages, 6126 KiB  
Article
Red and Blue-Black Tin Monoxide, SnO: Pitfalls, Challenges, and Helpful Tools in Crystal Structure Determination of Low-Intensity Datasets from Microcrystals
by Hans Reuter
Crystals 2023, 13(8), 1281; https://doi.org/10.3390/cryst13081281 - 19 Aug 2023
Cited by 1 | Viewed by 909
Abstract
The crystal structures of red and blue-black tin(II) oxide, SnO, have been determined for the first time by single-crystal X-ray diffraction. Blue-black SnO crystallizes in the tetragonal space group P4/nmm, representing a layer structure consisting of the square–pyramidally coordinated tin [...] Read more.
The crystal structures of red and blue-black tin(II) oxide, SnO, have been determined for the first time by single-crystal X-ray diffraction. Blue-black SnO crystallizes in the tetragonal space group P4/nmm, representing a layer structure consisting of the square–pyramidally coordinated tin and slightly distorted tetrahedrally coordinated oxygen atoms, in accordance with previous results. In contrast, red SnO crystallizes in the orthorhombic centrosymmetric space group Pbca rather than in the non-centrosymmetric space group Cmc21, as assumed for a long time. Its layer structure consists of very regular, trigonal–pyramidally coordinated tin atoms as well as trigonal–planar coordinated oxygen atoms. Special care was taken on space group determination, including lattice centering. C-centering could be excluded because of systematic absence violations detected when collecting and processing a primitive triclinic dataset and by generating precession images. In the absence of meaningful extinction conditions resulting from the very small crystal under examination, the structure was initially solved and refined in the triclinic space group P1. Subsequently, the observed atom coordinates were used to reconstruct the actual symmetry skeleton. The various possibilities to identify the correct space group starting from the triclinic solution are demonstrated, and the unique structural features of the crystal structure are visualized. Full article
Show Figures

Figure 1

17 pages, 6062 KiB  
Article
Energetics of Interfaces and Strain Partition in GaN/AlN Pseudomorphic Superlattices
by Theodoros Karakostas, Philomela Komninou and Vassilis Pontikis
Crystals 2023, 13(8), 1272; https://doi.org/10.3390/cryst13081272 - 17 Aug 2023
Viewed by 1346
Abstract
We present the results of a twofold experimental and computational study of (0001) GaN/AlN multilayers forming pseudomorphic superlattices. High-Resolution Transmission Electron Microscopy (HRTEM) shows that heterostructures with four c-lattice parameters thick GaN Quantum Wells (QW) are misfit-dislocation free. Accurate structural data are extracted [...] Read more.
We present the results of a twofold experimental and computational study of (0001) GaN/AlN multilayers forming pseudomorphic superlattices. High-Resolution Transmission Electron Microscopy (HRTEM) shows that heterostructures with four c-lattice parameters thick GaN Quantum Wells (QW) are misfit-dislocation free. Accurate structural data are extracted from HRTEM images via a new methodology optimizing the residual elastic energy stored in the samples. Total energy calculations are performed with several models analogous to the experimental QWs with increasing thicknesses of GaN, whereas this of the AlN barrier is kept fixed at n = 8 c-lattice parameters. With vanishing external stresses, minimum energy configurations of the studied systems correspond to different strain states. Linear elasticity accurately yields the corresponding lattice parameters, suppressing the need for on-purpose total energy calculations. Theoretically justified parabolic fits of the excess interfacial energy yield the values of interfacial stress and elastic stiffness as functions of the GaN QW thickness. Total species-projected densities of states and gap values extracted from there allow deciphering the effect of the evolving strain on the electronic structure of the superlattice. It is found that the gap energy decreases linearly with increasing the strain of the QW. These results are briefly discussed in the light shed by previous works from the literature. Full article
(This article belongs to the Special Issue Advances of GaN-Based Semiconductor Materials)
Show Figures

Figure 1

17 pages, 4552 KiB  
Article
The High-Pressure Phase Transition in Jamesonite: A Single-Crystal Synchrotron X-ray Diffraction Study
by Paola Comodi, Tonci Balić-Žunić, Maximiliano Fastelli, Michael Hanfland, Ines Collings and Azzurra Zucchini
Crystals 2023, 13(8), 1258; https://doi.org/10.3390/cryst13081258 - 15 Aug 2023
Viewed by 804
Abstract
The high-pressure behavior of jamesonite (FePb4Sb6S14, a = 4.08(3) Å, b = 19.08(3) Å, c = 15.67(3) Å, β= 91.89°, space group P21/c) has been investigated using in situ HP synchrotron X-ray [...] Read more.
The high-pressure behavior of jamesonite (FePb4Sb6S14, a = 4.08(3) Å, b = 19.08(3) Å, c = 15.67(3) Å, β= 91.89°, space group P21/c) has been investigated using in situ HP synchrotron X-ray single-crystal diffraction up to ~17 GPa with a diamond anvil cell under hydrostatic conditions. Results of the volume isothermal equation of state (EoS), determined by fitting the P-V data with a third-order Birch–Murnaghan (BM) EoS, are V0 = 1207.1(4) Å3, K0 = 36(1) GPa and K’ = 5.7(7). At high pressure, jamesonite undergoes a phase transition to an orthorhombic structure with a Pmcb space group (β-jamesonite). The analysis of β-jamesonite’s compressibility up to 16.6 GPa, studied by fitting the data with a second-order BM-EoS, gives V0 = 1027(2) Å3, K0 = 74(2) GPa. The comparison of the structural refinements at different pressures indicates that Fe, Pb and Sb do not change their coordination number over the whole investigated P range, respectively, 6 for Fe, 7 and 8 for Pb and 5 + 2 for Sb. However, a significant change occurs on the orientation of Sb lone electron pairs upon the phase transition in accordance with the change in symmetry. Furthermore, a discontinuity in the Fe chain evolution at the transition pressure is observed. Full article
Show Figures

Figure 1

16 pages, 3065 KiB  
Article
Hydrothermal Synthesis and Crystal Structure of Vesuvianite Compounds, Ca19Al13Si18O71(OH)7 and Sr19Fe12Ge19O72(OH)6
by Megan M. Smart, Cheryl A. Moore, Colin D. McMillen and Joseph W. Kolis
Crystals 2023, 13(8), 1257; https://doi.org/10.3390/cryst13081257 - 15 Aug 2023
Cited by 1 | Viewed by 732
Abstract
New compositions of synthetic vesuvianite were investigated using hydrothermal synthesis. High quality single crystals with the formula Ca19Al13Si18O71(OH)7 (I) having the vesuvianite-type structure were crystallized during a high temperature hydrothermal growth reaction. [...] Read more.
New compositions of synthetic vesuvianite were investigated using hydrothermal synthesis. High quality single crystals with the formula Ca19Al13Si18O71(OH)7 (I) having the vesuvianite-type structure were crystallized during a high temperature hydrothermal growth reaction. Starting materials of Al2O3 and CaSiO3 reacted at 670 °C and 2 kbar in 0.5 M aqueous alkali hydroxide mineralizer to form single crystals up to 0.25 mm per edge. Similar reactions employing SrO, Fe2O3, and GeO2 reacting at 580 °C and 2 kbar in 6 M aqueous alkali hydroxide mineralizers led to the formation of the analogous Sr19Fe12Ge19O72(OH)6 (II). These crystals were obtained in sizes up to 0.5 mm per edge. The structures of both compounds were refined in space group P4/nnc after careful evaluation of the diffraction data and subsequent test refinements. Elemental analysis indicated only the presence of Ca2+, Al3+, and Si4+ cations in I and only the presence of Sr2+, Fe3+, and Ge4+ cations in II, representing synthetic vesuvianite comprising the minimum number of unique cations. The use of larger cations than are typically found in natural vesuvianite, such as Sr2+, Fe3+, and Ge4+, resulted in an expanded crystalline lattice and extended the vesuvianite analogs to include an increasing variety of elements. Full article
(This article belongs to the Special Issue Mineralogical Crystallography (3rd Edition))
Show Figures

Figure 1

9 pages, 9002 KiB  
Article
H-Terminated Diamond MOSFETs on High-Quality Diamond Film Grown by MPCVD
by Wenxiao Hu, Xinxin Yu, Tao Tao, Kai Chen, Yucong Ye, Jianjun Zhou, Zili Xie, Yu Yan, Bin Liu and Rong Zhang
Crystals 2023, 13(8), 1221; https://doi.org/10.3390/cryst13081221 - 08 Aug 2023
Viewed by 1021
Abstract
Diamond-based transistors have been considered as one of the best choices due to the numerous advantages of diamond. However, difficulty in the growth and fabrication of diamond needs to be addressed. In this paper, high quality diamond film with an atomically flat surface [...] Read more.
Diamond-based transistors have been considered as one of the best choices due to the numerous advantages of diamond. However, difficulty in the growth and fabrication of diamond needs to be addressed. In this paper, high quality diamond film with an atomically flat surface was grown by microwave plasma chemical vapor deposition. High growth rate, as much as 7 μm/h, has been acquired without nitrogen doping, and the root mean square (RMS) of the surface roughness was reduced from 0.92 nm to 0.18 nm by using a pre-etched process. H-terminated diamond MOSFETs were fabricated on a high-quality epitaxial diamond layer, of which the saturated current density was enhanced. The hysteresis of the transfer curve and the shift of the threshold voltage were significantly reduced as well. Full article
(This article belongs to the Special Issue Epitaxial Growth of Crystalline Semiconductors)
Show Figures

Figure 1

12 pages, 4206 KiB  
Article
Structure and Thermal Stability of Two Estetrol Solvates
by Magda Monari, Emanuele Attolino, Gianfranco Lopopolo, Fabrizio Bosco and Massimo Gazzano
Crystals 2023, 13(8), 1211; https://doi.org/10.3390/cryst13081211 - 05 Aug 2023
Viewed by 950
Abstract
Two solvates of estetrol have been isolated and characterized by SCXRD and PXRD as well as by thermal analyses, morphology and spectroscopy. Estetrol monohydrate (Estetrol.H2O, S.G. P1, Z = 12) contains 12 molecules in its asymmetric unit with very subtle conformational [...] Read more.
Two solvates of estetrol have been isolated and characterized by SCXRD and PXRD as well as by thermal analyses, morphology and spectroscopy. Estetrol monohydrate (Estetrol.H2O, S.G. P1, Z = 12) contains 12 molecules in its asymmetric unit with very subtle conformational differences with one another but reveals an intricate network made of intermolecular H-bonds established with the neighbour estetrol molecules and with crystallization water. Each molecule of estetrol methanol hemisolvate (Estetrol.0.5CH3OH, S.G. C2, Z = 4) establishes six O-H…O bonds with six different neighbours and additional H-bonds with methanol. In both structures, estetrol molecules are organized in a head-to-tail arrangement that favours the formation of O-H…O interactions. The increased thermal stability of Estetrol.0.5CH3OH crystals with respect to Estetrol.H2O can be correlated to the strengthened network of H-bonds. Full article
(This article belongs to the Topic Advanced Structural Crystals)
Show Figures

Figure 1

25 pages, 11433 KiB  
Article
Coordination Polymers with a Pyrazine-2,5-diyldimethanol Linker: Supramolecular Networks through Hydrogen and Halogen Bonds
by Mahsa Armaghan, Tobias Stürzer and Christoph Janiak
Crystals 2023, 13(8), 1193; https://doi.org/10.3390/cryst13081193 - 31 Jul 2023
Viewed by 746
Abstract
In this paper, the synthesis and crystal structure of pyrazine-2,5-diyldimethanol (pyzdmH2, C6H8N2O2), a new symmetric water-soluble N,O-chelating tetra-dentate organic ligand, is reported and an environmentally friendly method is used to synthesize coordination compounds in water [...] Read more.
In this paper, the synthesis and crystal structure of pyrazine-2,5-diyldimethanol (pyzdmH2, C6H8N2O2), a new symmetric water-soluble N,O-chelating tetra-dentate organic ligand, is reported and an environmentally friendly method is used to synthesize coordination compounds in water under ambient conditions, from the reaction of pyzdmH2 with the halide salts of Cu(II), Zn(II), Hg(II) and Cd(II): {[Cu(pyzdmH2)0.5(µ-Br)(Br)(H2O)]·H2O}n 1, {[Zn2(pyzdmH2)(µ-Cl)(Cl)3(H2O)]·H2O}n 2, [Hg2(pyzdmH2)0.5(µ-Cl)2(Cl)2]n 3, {[Cd2(pyzdmH2)(µ-Cl)4]·H2O}n 4, and {[Cd2(pyzdmH2)(µ-Br)4]·H2O}n 5. Single-crystal X-ray diffraction analysis reveals that 13 are 1D coordination polymers and 4 and 5 are 3D coordination networks, all constructed by bridging pyrazine-2,5-diyldimethanol and halogen ions. The hydroxyl groups in the organic linker extend the 1D chains to non-covalent 3D networks. In all non-covalent and covalent 3D networks, water molecules are trapped by strong hydrogen bond interactions. Supramolecular analysis reveals strong O-H···O, O-H···N, O-H···X, and weak C-H···O, C-H···X (X = Cl, Br) hydrogen bonds, as well as π-π(pyrazine ring), metal-halogen···π(pyrazine ring), and O-H···ring(5-membered chelate ring) interactions. In addition, X···O weak halogen bonds are present in 15 (X = Cl and Br). Full article
Show Figures

Graphical abstract

11 pages, 2119 KiB  
Article
Microstructural Control by Cooling Rate in β-type and Sintered Ti-3.6Fe-5Zr-0.2B (Mass%) Alloy Fabricated by Spark Plasma Sintering and Heat Treatment
by Tomoyuki Homma and Takashi Washizu
Crystals 2023, 13(8), 1184; https://doi.org/10.3390/cryst13081184 - 29 Jul 2023
Viewed by 820
Abstract
The β-type and sintered Ti-3.6Fe-5Zr-0.2B (mass%) alloy has been consolidated by spark plasma sintering, followed by a β solution treatment (ST). In order to obtain a high-strength ductile balance, water quenching or air cooling is used after ST. Modification of sintering conditions, which [...] Read more.
The β-type and sintered Ti-3.6Fe-5Zr-0.2B (mass%) alloy has been consolidated by spark plasma sintering, followed by a β solution treatment (ST). In order to obtain a high-strength ductile balance, water quenching or air cooling is used after ST. Modification of sintering conditions, which leads to 100% of the relative density, improves the tensile ductility. The Fe addition causes a large local lattice and compressive strain to the bcc Ti lattice; in the water-quenched sample, α” martensite phases appear in the β matrix. When air cooling is applied after the ST, bimodal α lath phases are instead precipitated during the cooling in nanoscale, and the formation of α” martensite phases is suppressed. This results in high strength and better ductility when compared with those in the water-quenched sample, particularly in tensile properties. The air-cooled sample reveals attractive mechanical properties in both tension and compression modes. Full article
Show Figures

Figure 1

10 pages, 2530 KiB  
Article
In Situ Observation of High Bending Strain Recoverability in Au Nanowires
by Lingyi Kong, Guang Cao, Haofei Zhou and Jiangwei Wang
Crystals 2023, 13(8), 1159; https://doi.org/10.3390/cryst13081159 - 26 Jul 2023
Cited by 1 | Viewed by 720
Abstract
Metallic nanowires (NW) usually exhibit unique physical, mechanical, and chemical properties compared to their bulk counterparts. Despite extensive research on their mechanical behavior, the atomic-scale deformation mechanisms of metallic nanowires remain incompletely understood. In this study, we investigate the deformation behavior of Au [...] Read more.
Metallic nanowires (NW) usually exhibit unique physical, mechanical, and chemical properties compared to their bulk counterparts. Despite extensive research on their mechanical behavior, the atomic-scale deformation mechanisms of metallic nanowires remain incompletely understood. In this study, we investigate the deformation behavior of Au nanowires embedded with a longitudinal twin boundary (TB) under different loading rates using in situ nanomechanical testing integrated with atomistic simulations. The Au nanowires exhibit a recoverable bending strain of up to 27.5% with the presence of TBs. At low loading rates, the recoverable bending is attributed to the motion of stacking faults (SFs) and their interactions with TBs. At higher loading rates, the formation of high-angle grain boundaries and their reversible migration become dominant in Au nanowires. These findings enhance our understanding of the bending behavior of metallic nanowires, which could inspire the design of nanodevices with improved fatigue resistance and a large recoverable strain capacity. Full article
(This article belongs to the Special Issue Dislocations and Twinning in Metals and Alloys)
Show Figures

Figure 1

18 pages, 5700 KiB  
Article
Structure, Conformation and Contact Analyses of Six Aromatic Diamide Diesters
by Islam Ali Osman, Vickie McKee, Christian Jelsch and John F. Gallagher
Crystals 2023, 13(7), 1133; https://doi.org/10.3390/cryst13071133 - 20 Jul 2023
Viewed by 891
Abstract
Six meta-substituted isophthalamide diesters (DxE) and pyridinedicarboxamides (PxE) are reported with spectroscopic and crystal structure analyses (D = meta-C6H4; P = meta-pyridine; xE = 2-/3-/4-ethyl ester substitution). Comparisons are made between [...] Read more.
Six meta-substituted isophthalamide diesters (DxE) and pyridinedicarboxamides (PxE) are reported with spectroscopic and crystal structure analyses (D = meta-C6H4; P = meta-pyridine; xE = 2-/3-/4-ethyl ester substitution). Comparisons are made between the solid-state and minimised structures from ab initio computational calculations. The six compounds are potentially useful ligands for metal-complex coordination, spanning a range of molecular conformations. D2E adopts a planar molecular structure, as influenced by the C-H⋯O intramolecular interactions with all 34 nonhydrogen atoms within 0.1 Å of the D2E mean molecular plane. Extensive intermolecular ring⋯ring stacking arises with the shortest interplanar C⋯C of 3.372(2) Å. For D3E (Z′ = 4) and D4E, the hierarchy of intermolecular interactions is the determining factor driving the crystal structure formation with concomitant twinning, as influenced by the weaker interactions. In the pyridine-related P2E, the O1W water molecule (site occupancy = 0.441(5)) forms four hydrogen bonds, as follows: (i) O1W−H⋯O=C, (ii) O1W−H⋯π(arene) and (iii) two aromaticC−H⋯O1W. The meta- and para-substituted PxE·2(H2O) structures (x = 3 or 4) adopt open conformations with pairs of hydrogen-bonded water molecules located in molecular niches between the flanking benzamide ester groups. The Hirshfeld surface, two-dimensional fingerprint plots and contact enrichment ratio were investigated to statistically analyse the different types of intermolecular interactions. Full article
(This article belongs to the Section Organic Crystalline Materials)
Show Figures

Figure 1

16 pages, 15230 KiB  
Article
Different Cooling Histories of Ultrahigh-Temperature Granulites Revealed by Ti-in-Quartz: An Electron Microprobe Approach
by Di Zhang, Yi Chen, Qian Mao, Shujuan Jiao, Bin Su, Si Chen and Kyaing Sein
Crystals 2023, 13(7), 1116; https://doi.org/10.3390/cryst13071116 - 17 Jul 2023
Viewed by 743
Abstract
The cooling history of granulite is crucial to understanding tectonic scenarios of the continental crust. Ti-in-quartz, a useful indicator of temperature, can decipher the thermal evolution of crustal rocks. Here we apply the Ti-in-quartz (TitaniQ) thermometer to ancient ultrahigh-temperature (UHT) granulites from the [...] Read more.
The cooling history of granulite is crucial to understanding tectonic scenarios of the continental crust. Ti-in-quartz, a useful indicator of temperature, can decipher the thermal evolution of crustal rocks. Here we apply the Ti-in-quartz (TitaniQ) thermometer to ancient ultrahigh-temperature (UHT) granulites from the Khondalite Belt (KB) in the North China Craton (NCC) and young UHT granulites from the Mogok Metamorphic Belt (MMB), Myanmar. Ti content in quartz was analyzed using a highly precise method constructed in a CAMECA SXFive electron probe microanalyzer (EPMA). The granulites from the two localities show different quartz Ti contents with a constant deforced beam of 10 μm. Matrix quartz and quartz inclusions from the NCC granulites have 57–241 ppm and 65–229 ppm, respectively, corresponding to the TitaniQ temperatures of 653–810 °C and 666–807 °C. The calculated temperatures are significantly lower than the peak temperatures (850–1096 °C) obtained by other methods, due to the formation of abundant rutile exsolution rods in quartz during cooling. Thus, the low calculated temperatures for the NCC granulites reflect a cooling state near or after the exsolution of rutile from quartz, most likely caused by a slow cooling process. However, the matrix quartz from the MMB granulites is exsolution-free and records higher Ti contents of 207–260 ppm and higher metamorphic temperatures of 894–926 °C, close to the peak UHT conditions. This feature indicates that the MMB granulites underwent rapid cooling to overcome Ti loss from quartz. Therefore, determining the amount of Ti loss from quartz by diffusion can provide new insight into the cooling behavior of UHT granulites. When a large deforced beam of 50 μm was used to cover the rutile rods, the matrix quartz in the KB granulites could also yield the TitaniQ temperatures above 900 °C. Thus, our new data suggest that the TitaniQ thermometer could be useful for revealing UHT conditions. Full article
(This article belongs to the Special Issue Mineralogical Crystallography (3rd Edition))
Show Figures

Figure 1

12 pages, 2905 KiB  
Article
Experimental Observation of Possible Pressure-Induced Phase Transformation in GdAlO3 Perovskite Using In Situ X-ray Diffraction
by Maria Mora, Andriy Durygin, Vadym Drozd, Shanece Esdaille, Jiuhua Chen, Surendra Saxena, Xue Liang and Leonid Vasylechko
Crystals 2023, 13(7), 1060; https://doi.org/10.3390/cryst13071060 - 05 Jul 2023
Viewed by 988
Abstract
Gadolinium aluminate perovskite (GdAlO3) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R [...] Read more.
Gadolinium aluminate perovskite (GdAlO3) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R3¯c) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., VA/VB for ABX3 general notation) in the Pbnm phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO3, CaGeO3, MgSiO3 and NaMgF3). Pressure–volume data of the Pbnm phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (Ko) of 216 ± 7 GPa with a pressure derivative of the bulk modulus (Ko) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transformation from orthorhombic to a higher symmetry structure previously predicted in GdAlO3 perovskite. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
Show Figures

Figure 1

18 pages, 4740 KiB  
Article
Grain Size Distribution of DP 600 Steel Using Single-Pass Asymmetrical Wedge Test
by Urška Klančnik, Peter Fajfar, Jan Foder, Heinz Palkowski, Jaka Burja and Grega Klančnik
Crystals 2023, 13(7), 1055; https://doi.org/10.3390/cryst13071055 - 04 Jul 2023
Viewed by 1002
Abstract
Grain size distribution after the completion of a phase transformation was studied through the laboratory-controlled hot-plastic deformation of dual phase 600 (DP 600) steel using a specially prepared asymmetric single-pass hot-rolling wedge test with a refined reheating grain size instead of the usual [...] Read more.
Grain size distribution after the completion of a phase transformation was studied through the laboratory-controlled hot-plastic deformation of dual phase 600 (DP 600) steel using a specially prepared asymmetric single-pass hot-rolling wedge test with a refined reheating grain size instead of the usual coarse-grained starting microstructure observed in practice. The experiment was performed to reduce generally needed experimental trials to observe the microstructure development at elevated temperatures, where stable and unstable conditions could be observed as in the industrial hot-rolling practice. For this purpose, experimental stress–strain curves and softening behaviors were used concerning FEM simulations to reproduce in situ hot-rolling conditions to interpret the grain size distribution. The presented study revealed that the usual approach found in the literature for microstructure investigation and evolution with a hot-rolling wedge test was deficient concerning the observed field of interest. The degree of potential error concerning the implemented deformation per notch position, as well as the stress–strain rate and related mean flow stresses, were highly related to the geometry of the specimen and the material behavior itself, which could be defined by the actual hardening and softening kinetics (recrystallization and grain growth at elevated temperatures and longer interpass times). The grain size distribution at 1100–1070 °C was observed up to a 3.45 s−1 strain rate and, based on its stable forming behavior according to the FEM simulations and the optimal refined grain size, the optimal deformation was positioned between e = 0.2 and e = 0.5. Full article
Show Figures

Figure 1

12 pages, 8872 KiB  
Article
An Investigation of In Vitro Bioactivities and Cytotoxicities of Spray Pyrolyzed Apatite Wollastonite Glass-Ceramics
by Andualem Belachew Workie, Henni Setia Ningsih, Wen-Ling Yeh and Shao-Ju Shih
Crystals 2023, 13(7), 1049; https://doi.org/10.3390/cryst13071049 - 02 Jul 2023
Cited by 2 | Viewed by 1047
Abstract
An apatite-wollastonite glass ceramic (AWGC) has been recognized as one of the popular bioactive materials due to its good osteoconductivity and high mechanical properties in the field of tissue engineering. Various processes have been developed to fabricate AWGCs. Among them, the sol-gel process [...] Read more.
An apatite-wollastonite glass ceramic (AWGC) has been recognized as one of the popular bioactive materials due to its good osteoconductivity and high mechanical properties in the field of tissue engineering. Various processes have been developed to fabricate AWGCs. Among them, the sol-gel process is one of the most popular processes. However, sol-gel has the drawbacks of discontinuous processing and long processing time, making it unsuitable for mass production. This study demonstrates a successful synthesis of AWGCs using a spray pyrolysis method to overcome these drawbacks, and the prepared pellets were sintered at temperatures of 700, 800, 900, 1000, and 1100 °C for four hours. In addition, X-ray diffraction, scanning electron microscopy, and X-ray energy-dispersive spectroscopy were used to obtain the phase composition, morphology, and chemical information of AWGCs. For bioactive measurements, among these AWGC samples, the 1100 °C sintered sample reveals the highest bioactivity. The MTT result indicates that all AWGCs are not non-toxic to the MC3T3-E1 cells and increase the growth rate of MC3T3-E1 cells. Full article
(This article belongs to the Special Issue Advances in New Functional Biomaterials for Medical Applications)
Show Figures

Figure 1

19 pages, 25062 KiB  
Article
Phase-Field Simulation of the Microstructure Evolution in the Eutectic Alloy NiAl-31Cr-3Mo
by Michael Kellner, Camelia Schulz, Alexander Kauffmann, Martin Heilmaier and Britta Nestler
Crystals 2023, 13(7), 1046; https://doi.org/10.3390/cryst13071046 - 01 Jul 2023
Cited by 2 | Viewed by 1012
Abstract
The directionally solidified eutectic alloy NiAl-(Cr,Mo) is a promising candidate for structural applications at high temperatures, due to its increased creep resistance compared to its single phase B2ordered NiAl counterpart. This system yields an eutectic trough connecting the invariant reactions of the [...] Read more.
The directionally solidified eutectic alloy NiAl-(Cr,Mo) is a promising candidate for structural applications at high temperatures, due to its increased creep resistance compared to its single phase B2ordered NiAl counterpart. This system yields an eutectic trough connecting the invariant reactions of the ternary alloys NiAl-Cr and NiAl-Mo. During directional solidification (DS) along this trough the evolved microstructures of the two-phase eutectic is changing from fibrous to lamellar and back to fibrous morphology while increasing and decreasing the amounts of Mo and Cr, respectively. To investigate these effects in the morphology, the phase-field method has proven to be predestined in the last decades. However, as the modeling of quaternary systems is challenging for the simulation with a grand potential based phase-field model, the focus of this work is on the generation of a material model for one defined compound namely NiAl-31Cr-3Mo. The modeling is validated by investigating the microstructure evolution in two- and three-dimensional simulations of the DS process for two different growth velocities and by investigating their undercooling spacing relationships. The evolving microstructures obtained from three-dimensional large-scale simulations are presented and validated with corresponding micrographs from scanning electron microscopy (SEM) of directionally solidified samples with the same growth velocities. The simulation results show the theoretically expected behaviors and are in qualitative and quantitative accordance with DS experiments. The study of NiAl-31Cr-3Mo serves as the basis for a comprehensive data-driven analysis of microstructure properties and system quantities of the entire quaternary material NiAl-(Cr,Mo). With this, an accelerated design of advanced materials is promoted. Full article
(This article belongs to the Special Issue Recently Research on Eutectic Alloy Materials)
Show Figures

Figure 1

17 pages, 3227 KiB  
Review
Progress in Ammonothermal Crystal Growth of Gallium Nitride from 2017–2023: Process, Defects and Devices
by Nathan Stoddard and Siddha Pimputkar
Crystals 2023, 13(7), 1004; https://doi.org/10.3390/cryst13071004 - 23 Jun 2023
Cited by 4 | Viewed by 1683
Abstract
Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium [...] Read more.
Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium nitride grown on foreign substrates such as sapphire and silicon carbide, the best performance values consistently come from devices built on bulk-grown gallium nitride from native seeds. The most prominent and promising of the bulk growth methods is the ammonothermal method of high-pressure solution growth. The state-of-the-art from the last five years in ammonothermal gallium nitride technology is herein reviewed within the general categories of growth technology, characterization and defects as well as device performance. Full article
(This article belongs to the Special Issue Research in GaN-based Materials and Devices)
Show Figures

Figure 1

10 pages, 5863 KiB  
Article
In Situ Study on Cu-to-Cu Thermal Compression Bonding
by Tongjun Niu, Ke Xu, Chao Shen, Tianyi Sun, Justin Oberst, Carol A. Handwerker, Ganesh Subbarayan, Haiyan Wang and Xinghang Zhang
Crystals 2023, 13(7), 989; https://doi.org/10.3390/cryst13070989 - 21 Jun 2023
Viewed by 1424
Abstract
Cu-to-Cu thermal compression bonding (TCB) has emerged as a promising solution for ultrafine pitch packaging in 3D integrated circuit technologies. Despite the progress made by conventional Cu-to-Cu TCB methods in achieving good mechanical strength of the Cu bonds, the bonding processes generally require [...] Read more.
Cu-to-Cu thermal compression bonding (TCB) has emerged as a promising solution for ultrafine pitch packaging in 3D integrated circuit technologies. Despite the progress made by conventional Cu-to-Cu TCB methods in achieving good mechanical strength of the Cu bonds, the bonding processes generally require high temperature and high pressure, which may degrade the performance and reliability of the device. Therefore, it is imperative to investigate the processing parameters to understand the bonding mechanism and achieve effective TCB at a low temperature and low pressure. Here, we developed an in situ TCB technique inside a scanning electron microscope. The in situ TCB method enables a real-time observation of bonding development, which provides critical insights into how the texture and microstructure of Cu bumps may influence the creep and surface diffusion during the bonding process. This work features a strategy to advance our understanding of the bonding mechanisms and provides insight into tailoring the microstructure of Cu for bonding at a low temperature and low pressure. Full article
(This article belongs to the Section Crystalline Metals and Alloys)
Show Figures

Figure 1

16 pages, 3685 KiB  
Article
The Multi-Analytical Characterization of Calcium Oxalate Phytolith Crystals from Grapevine after Treatment with Calcination
by Gwenaëlle Trouvé, Laure Michelin, Damaris Kehrli, Ludovic Josien, Séverinne Rigolet, Bénédicte Lebeau and Reto Gieré
Crystals 2023, 13(6), 967; https://doi.org/10.3390/cryst13060967 - 18 Jun 2023
Cited by 1 | Viewed by 1478
Abstract
Calcium oxalate phytoliths are one of the most prominent types of Ca speciation in the plant kingdom, and they store extensive amounts of carbon in crystalline form. Ca phytoliths were investigated in the root, trunk, and bark of Vitis vinifera Chasselas from a [...] Read more.
Calcium oxalate phytoliths are one of the most prominent types of Ca speciation in the plant kingdom, and they store extensive amounts of carbon in crystalline form. Ca phytoliths were investigated in the root, trunk, and bark of Vitis vinifera Chasselas from a vineyard in Alsace, France. A multi-analytical approach was used, which included SEM coupled with EDX spectroscopy, XRD, XRF, TGA, and 13C-NMR spectroscopy. These techniques revealed that phytoliths are composed of crystalline calcium oxalate monohydrate (whewellite). The whewellite crystals exhibited mostly equant or short-prismatic habits in all of the three studied grapevine parts, but bipyramidal crystals also occurred. Raphide crystals were only observed in the root, where they were abundant. Instead of using wet chemical procedures to extract the mineral components from the organic parts of the biomass, a thermal treatment via calcination was chosen. The suitable temperature of calcination was determined through TGA experiments. The calcination of the biomass samples at 250 °C enhanced the amounts of Ca phytoliths in the residual chars. The thermal treatment, however, affected the appearance of the Ca oxalate crystals by producing surfaces that displayed macroporosity and by creating fractures. For calcination at both 300 °C and 350 °C, Ca oxalate lost a molecule of carbon monoxide to form Ca carbonate, and the modifications of the original crystal surfaces were more pronounced than those observed after thermal treatment at 250 °C. Full article
(This article belongs to the Topic Advanced Structural Crystals)
Show Figures

Figure 1

21 pages, 7219 KiB  
Article
TIC Reorientation under Electric and Magnetic Fields in Homeotropic Samples of Cholesteric LC with Negative Dielectric Anisotropy
by Patrick Oswald, Guilhem Poy and Jordi Ignés-Mullol
Crystals 2023, 13(6), 957; https://doi.org/10.3390/cryst13060957 - 15 Jun 2023
Viewed by 650
Abstract
In this paper, we numerically and experimentally show that the director field orientation degeneracy within the Translationally Invariant Configuration (TIC) of a cholesteric liquid crystal under an electric field can be lifted by imposing a magnetic field B parallel to the electrodes. [...] Read more.
In this paper, we numerically and experimentally show that the director field orientation degeneracy within the Translationally Invariant Configuration (TIC) of a cholesteric liquid crystal under an electric field can be lifted by imposing a magnetic field B parallel to the electrodes. The configuration can be either parallel or perpendicular to the magnetic field depending on the values of the sample thickness, pitch, and applied voltage, with two equiprobable orientations in each case. The transition between the parallel and perpendicular orientations has hysteresis, suggesting that it is first order. When B is slightly tilted with respect to the electrode plane, the indeterminacy on the TIC orientation is removed when the TIC is directed along B. Full article
Show Figures

Figure 1

17 pages, 6010 KiB  
Article
Spectroscopic and Crystallographic Characterization of Two Hydrochloride Cathinones: 1-(4-fluoro-3-methylphenyl)-2-(pyrrolidin-1-yl)pentan-1-one (4-F-3-Me-α-PVP) and N-ethyl-2-amino-1-phenylheptan-1-one (N-ethylheptedrone)
by Marcin Rojkiewicz, Piotr Kuś, Joachim Kusz, Maria Książek and Dorota Staszek
Crystals 2023, 13(6), 934; https://doi.org/10.3390/cryst13060934 - 10 Jun 2023
Viewed by 847
Abstract
In this paper, two cathinone derivatives, 4F-3Me-α-PVP and N-ethylheptedrone, seized on the illegal drug market in Poland, were described and characterized by various instrumental analytical methods. The compounds were characterized by electrospray ionization mass spectrometry, high-resolution mass spectrometry, gas chromatography–mass spectrometry, infrared spectroscopy, [...] Read more.
In this paper, two cathinone derivatives, 4F-3Me-α-PVP and N-ethylheptedrone, seized on the illegal drug market in Poland, were described and characterized by various instrumental analytical methods. The compounds were characterized by electrospray ionization mass spectrometry, high-resolution mass spectrometry, gas chromatography–mass spectrometry, infrared spectroscopy, X-ray crystallography, thermogravimetric analysis, differential scanning calorimetry and nuclear magnetic resonance spectroscopy. The two tested compounds were confirmed as 1-(4-fluoro-3-methylphenyl)-2-(pyrrolidin-1-yl)pentan-1-one and N-ethyl-2-amino-1-phenylheptan-1-one hydrochlorides; both are cathinone derivatives available on the market for new psychoactive substances (NPS). The obtained analytical data should be useful for forensic and toxicological purposes in the rapid and reliable identification of compounds. Full article
Show Figures

Figure 1

11 pages, 3112 KiB  
Article
Improvement of Mg-Doped GaN with Shutter-Controlled Process in Plasma-Assisted Molecular Beam Epitaxy
by Ying-Chieh Wang, Ikai Lo, Yu-Chung Lin, Cheng-Da Tsai and Ting-Chang Chang
Crystals 2023, 13(6), 907; https://doi.org/10.3390/cryst13060907 - 01 Jun 2023
Viewed by 955
Abstract
Mg-doped GaN was grown by plasma-assisted molecular beam epitaxy (PAMBE) on a Fe-doped GaN template substrate by employing a shutter-controlled process. The transition from n-type to p-type conductivity of Mg-doped GaN in relation to the N/Ga flux ratio was studied. The [...] Read more.
Mg-doped GaN was grown by plasma-assisted molecular beam epitaxy (PAMBE) on a Fe-doped GaN template substrate by employing a shutter-controlled process. The transition from n-type to p-type conductivity of Mg-doped GaN in relation to the N/Ga flux ratio was studied. The highest p-type carrier concentration in this series was 3.12 × 1018 cm−3 under the most N-rich condition. By modulating the shutters of different effusion cells for the shutter-controlled process, a wide growth window for p-type GaN was obtained. It was found that the presence of Mg flux effectively prevents the formation of structural defects in GaN epi-layers, resulting in the improvement of crystal quality and carrier mobility. Full article
(This article belongs to the Special Issue Materials and Devices Grown via Molecular Beam Epitaxy)
Show Figures

Figure 1

13 pages, 2779 KiB  
Article
Structural and Magnetic Properties of the {Cr(pybd)3[Cu(cyclen)]2}(BF4)4 Heteronuclear Complex
by Fabio Santanni, Laura Chelazzi, Lorenzo Sorace, Grigore A. Timco and Roberta Sessoli
Crystals 2023, 13(6), 901; https://doi.org/10.3390/cryst13060901 - 01 Jun 2023
Viewed by 1150
Abstract
Heterotopic ligands containing chemically different binding centers are appealing candidates for obtaining heteronuclear metal complexes. By exploiting this strategy, it is possible to introduce different paramagnetic centers characterized by specific anisotropic magnetic properties that make them distinguishable when weakly magnetically coupled. This molecular [...] Read more.
Heterotopic ligands containing chemically different binding centers are appealing candidates for obtaining heteronuclear metal complexes. By exploiting this strategy, it is possible to introduce different paramagnetic centers characterized by specific anisotropic magnetic properties that make them distinguishable when weakly magnetically coupled. This molecular approach has great potential to yield multi-spin adducts capable of mimicking logical architectures necessary for quantum information processing (QIP), i.e., quantum logic gates. A possible route for including a single-ion magnetic center within a finite-sized heterometallic compound uses the asymmetric (1-pyridyl)-butane-1,3-dione (pybd) ligand reported in the literature for obtaining Cr3+−Cu2+ metallo-cages. To avoid the formation of cages, we adopted the cyclen (1,4,7,10-tetraazacyclododecane) ligand as a “capping” agent for the Cu2+ ions. We report here the structural and magnetic characterization of the unprecedented adduct {Cr(pybd)3[Cu(cyclen)]2}(BF4)4, whose structure is characterized by a central Cr3+ ion in a distorted octahedral coordination environment and two peripheral Cu2+ ions with square-pyramidal coordination geometries. As highlighted by Continuous Wave Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetometry measurements, this adduct shows negligible intramolecular magnetic couplings, and it maintains the characteristic EPR signals of Cr3+ and Cu2+ moieties when diluted in frozen solutions. Full article
(This article belongs to the Special Issue The Polyhedral Face of Coordination Chemistry)
Show Figures

Figure 1

12 pages, 3420 KiB  
Article
C–H…X (X = F, Cl, Br, I) Versus π-Stacking in the Crystal Packing of Compounds Containing the {M(tpy)X3} Motif
by Catherine E. Housecroft and Edwin C. Constable
Crystals 2023, 13(6), 885; https://doi.org/10.3390/cryst13060885 - 28 May 2023
Viewed by 919
Abstract
Analysis of the data in the Cambridge Structural Database (CSD) for compounds containing an {M(tpy)X3} motif (tpy = 2,2’:6’,2”-terpyridine, M = any metal, X = F, Cl, Br, I) reveals 17 isostructural mononuclear [M(tpy)X3] compounds crystallizing without lattice solvent; [...] Read more.
Analysis of the data in the Cambridge Structural Database (CSD) for compounds containing an {M(tpy)X3} motif (tpy = 2,2’:6’,2”-terpyridine, M = any metal, X = F, Cl, Br, I) reveals 17 isostructural mononuclear [M(tpy)X3] compounds crystallizing without lattice solvent; both face-to-face π-stacking of pyridine rings and C–H3/H3’…X hydrogen bonding appear to be equally important. Regardless of coordination number (CN = 6, 7 or 8) and nuclearity (mono- or dinuclear), a recurring packing feature in other compounds containing an {M(tpy)X3} unit is the presence of bifurcated Cl…H3/H3’ interactions, complemented in some cases by Cl…H5’/H3” interactions, consistent with the acidic H3, H3’, H5’, and H3” atoms of a coordinated tpy ligand. Octahedral [M(tpy)F3] complexes crystallize as hydrates with strong F…H–OH hydrogen bonding dominating the crystal packing. Full article
Show Figures

Figure 1

17 pages, 2946 KiB  
Article
Extending Ab Initio Phasing up to 2.2 Å Resolution: New Superposition Techniques
by Maria Cristina Burla, Benedetta Carrozzini, Giovanni Luca Cascarano, Carmelo Giacovazzo and Giampiero Polidori
Crystals 2023, 13(6), 874; https://doi.org/10.3390/cryst13060874 - 26 May 2023
Viewed by 483
Abstract
Patterson superposition techniques are a historical method for solving the structures of small molecules ab initio, provided they contain heavy atoms in the unit cell. In the 1990s, they were combined with effective EDM procedures and succeeded in the crystal structure solution of [...] Read more.
Patterson superposition techniques are a historical method for solving the structures of small molecules ab initio, provided they contain heavy atoms in the unit cell. In the 1990s, they were combined with effective EDM procedures and succeeded in the crystal structure solution of macromolecular structures with resolution data up to 1.6–1.9 Å. In this paper we enlarge the concept of Patterson superposition by replacing it with the vector superposition concept. We show, indeed, that besides Patterson other Fourier syntheses may also be used for the superposition of the interatomic vectors. Five Fourier syntheses are described and used in the practical applications. We show that even macromolecular structures with 2.2 Å data resolution may be solved via the new approach. Full article
(This article belongs to the Special Issue Nucleic Acid Crystallography Volume II)
Show Figures

Figure 1

17 pages, 4020 KiB  
Article
Impact of Tuned Oxidation on the Surface Energy of Sintered Samples Produced from Atomised B-Doped Al-Cu-Fe Quasicrystalline Powders
by Monika Kušter, Janez Kovač, Zoran Samardžija, Matej Komelj, Sorour Semsari Parapari, Matejka Podlogar, Jean-Marie Dubois and Sašo Šturm
Crystals 2023, 13(6), 859; https://doi.org/10.3390/cryst13060859 - 23 May 2023
Cited by 2 | Viewed by 1434
Abstract
Super-hydrophobic surfaces and coatings have stimulated a great deal of research, with the aim being to achieve better wetting properties. Factors such as surface chemistry and roughness play an important role in changing the surface energy, which in turn leads to changes in [...] Read more.
Super-hydrophobic surfaces and coatings have stimulated a great deal of research, with the aim being to achieve better wetting properties. Factors such as surface chemistry and roughness play an important role in changing the surface energy, which in turn leads to changes in the wettability. Here, we have analysed the time dependence of the oxide layer and possible surface adsorbates on the surface topography of an Al59Cu25Fe13B3 quasicrystalline material in relation to changes in the wettability. The quasicrystalline matrix phase was 94% of the sample volume, and it was covered by a very smooth, amorphous oxide layer. The AlB12 and AlFe2B2 boron-rich phases were embedded in the quasicrystalline material as a result of the 3 at.% boron addition, which made atomisation of the material a simpler process. Under ambient conditions, the sample was naturally covered by an oxide layer; therefore, it is referred to as “surfenergy” to distinguish it from the conventional surface energy of a bare quasicrystal surface. The growth of the oxide layer with atmospheric ageing and annealing at 500 °C in air for various times was investigated for both cases. The phase most prone to oxidation was the boron-rich AlFe2B2, which influenced the topography of the surface and accordingly the wetting behaviour of the specimen. We demonstrated that the surfenergy depends on the polar component, which is the most sensitive to the operating conditions. A correlation between the surfenergy components and the surface roughness was found. In addition, theoretical models to determine the wettability were included. Full article
(This article belongs to the Section Crystalline Metals and Alloys)
Show Figures

Graphical abstract

10 pages, 2045 KiB  
Article
In Silico Interactome of a Room-Temperature Ferroelectric Nematic Material
by Richard J. Mandle
Crystals 2023, 13(6), 857; https://doi.org/10.3390/cryst13060857 - 23 May 2023
Cited by 3 | Viewed by 1119
Abstract
The ferroelectric nematic (NF) phase, characterised by the combination of orientational and polar order, offers unique properties that are challenging to replicate in other systems. Understanding the molecular structure requirements for generating the NF phase is crucial for the design [...] Read more.
The ferroelectric nematic (NF) phase, characterised by the combination of orientational and polar order, offers unique properties that are challenging to replicate in other systems. Understanding the molecular structure requirements for generating the NF phase is crucial for the design of new materials with enhanced properties. This study investigates UUQU-4-N, a room-temperature NF material, using fully atomistic molecular dynamics simulations. UUQU-4-N does not spontaneously form an apolar nematic phase in silico, but exhibits a stable polar nematic configuration akin to the NF phase. The polar order remains significant and near saturation throughout the simulations. The study also examines the cylindrical pair correlation functions, providing insights into the preferred pairing modes and intermolecular interactions which we can then attribute to specific molecular features. We then simulate structural variants of UUQU-4-N, highlighting the potential for developing further examples of near-room-temperature ferroelectric nematic materials via the manipulation of the fluorination pattern, variations in terminal chain length, and replacement of the difluoromethyleneoxy linker. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
Show Figures

Figure 1

22 pages, 37232 KiB  
Article
Crystal Structure, Thermal Expansion and Luminescence of Ca10.5−xNix(VO4)7
by Houri S. Rahimi Mosafer, Wojciech Paszkowicz, Roman Minikayev, Christine Martin, Mirosław Kozłowski, Oksana Chukova, Yaroslav Zhydachevskyy and Serhii Nedilko
Crystals 2023, 13(5), 853; https://doi.org/10.3390/cryst13050853 - 22 May 2023
Cited by 1 | Viewed by 1204
Abstract
The structural and luminescence properties of a new material, Ca10.5−xNix(VO4)7, formed by substitution of a fraction of calcium by nickel, are studied as a function of the Ni content (x). The powder [...] Read more.
The structural and luminescence properties of a new material, Ca10.5−xNix(VO4)7, formed by substitution of a fraction of calcium by nickel, are studied as a function of the Ni content (x). The powder X-ray diffraction results for the polycrystals, synthesized using a solid-state reaction method, show that in the studied temperature range (300–1150 K), the structure of the unsubstituted material (space group R3c, whitlockite-β-Ca3(PO4)2 structure type) is conserved up to the solubility limit, x = 0.72(2), determined on the basis of variation of unit cell size with x. The samples of nominal composition exceeding this limit contain a significant amount of the impurity phase.The structural refinements demonstrate that Ni atoms preferentially occupy the M5 site (one of the five independent Ca sites, M1–M5). The unit cell size was equally studied in the range of 300–1150 K, leading to the determination of the thermal expansion coefficients. It was found that with rising Ni content, the room temperature volumetric thermal expansion decreases from 41.80 MK−1 (x = 0.16) to 39.24 MK−1 (x = 0.66) and to 38.92 MK−1 at the solubility limit, this reduction being in line with earlier reported data for x=0. In the unit cell variation, around 800–900 K, a weak anomaly is observed, detectable most clearly for the axial ratio; it is also visible at thermal expansion coefficient temperature dependence. Substitution of Ca by Ni ions reduces the optical band gap of Ca10.5−xNix(VO4)7 from 3.56 (x = 0) to 3.29 and 3.16 eV observed for Ni-containing samples (x = 0.33 and 0.66, respectively). Observed bands in the absorption and photoluminescence spectra are assigned to electronic transitions in both VO43 groups and Ni2+ ions, confirming that Ni mainly occupies the M5 site. The band gap narrowing and decrease in photoluminescence intensity when the Ni concentration increases makes Ni-substituted compounds attractive for application, e.g., as photocatalysts. Full article
Show Figures

Figure 1

19 pages, 9053 KiB  
Article
Reflections of High-Frequency Pulsed Ultrasound by Underwater Acoustic Metasurfaces Composed of Subwavelength Phase-Gradient Slits
by Jin-Chen Hsu, Herwandi Alwi, Chun-Hao Wei, Kai-Li Liao and Che-Ting Huang
Crystals 2023, 13(5), 846; https://doi.org/10.3390/cryst13050846 - 20 May 2023
Cited by 3 | Viewed by 1218
Abstract
We numerically and experimentally investigated the behavior of high-frequency underwater ultrasounds reflected by gradient acoustic metasurfaces. Metasurfaces were fabricated with a periodic array of gradient slits along the surface of a steel specimen. The finite element method was adopted for the acoustics–structure interaction [...] Read more.
We numerically and experimentally investigated the behavior of high-frequency underwater ultrasounds reflected by gradient acoustic metasurfaces. Metasurfaces were fabricated with a periodic array of gradient slits along the surface of a steel specimen. The finite element method was adopted for the acoustics–structure interaction problem to design the metasurfaces and simulate the reflected fields of the incident ultrasound. Our metasurfaces yielded anomalous reflection, specular reflection, apparent negative reflection, and radiation of surface-bounded modes for ultrasonic waves impinging on the metasurfaces at different incident angles. The occurrence of these reflection behaviors could be explained by the generalized Snell’s law for a gradient metasurface with periodic supercells. We showed that at some incident angles, strong anomalous reflection could be generated, which could lead to strong retroreflection at specific incident angles. Furthermore, we characterized the time evolution of the reflections using pulsed ultrasound. The simulated transient process revealed the formation of propagating reflected ultrasound fields. The experimentally measured reflected ultrasound signals verified the distinct reflection behaviors of the metasurfaces; strong anomalous reflection steering the ultrasound pulse and causing retroreflection was observed. This study paves the way for designing underwater acoustic metasurfaces for ultrasound imaging and caustic engineering applications using pulsed ultrasound in the high-frequency regime. Full article
Show Figures

Figure 1

13 pages, 8480 KiB  
Article
Role of Hydroxy Group in the Electro-Optical Properties of Polymer-Dispersed Liquid Crystals
by Meina Yu, Jianjun Xu, Lingpeng Luo, Luoning Zhang, Yanzi Gao, Cheng Zou, Qian Wang, Huiyun Wei, Xiao Wang and Huai Yang
Crystals 2023, 13(5), 843; https://doi.org/10.3390/cryst13050843 - 19 May 2023
Cited by 3 | Viewed by 1242
Abstract
In this work, hydroxylated compounds are applied to prepare polymer-dispersed liquid crystal (PDLC) films and the role of the hydroxy group is studied in detail by comparing the effects of the hydroxylated acrylate monomer, the hydroxylated mesogenic component and their corresponding non-hydroxylated components. [...] Read more.
In this work, hydroxylated compounds are applied to prepare polymer-dispersed liquid crystal (PDLC) films and the role of the hydroxy group is studied in detail by comparing the effects of the hydroxylated acrylate monomer, the hydroxylated mesogenic component and their corresponding non-hydroxylated components. It is revealed that the hydroxylated acrylate monomer plays a more important role in modifying the morphology of the polymer matrix and thereby the electro-optical performance of the PDLC films. Parameters of the polymer matrix, such as size and density of voids, can be affected by various components, but only the hydroxylated acrylate monomer can alter its type from the typical Swiss-cheese type to the polymer-microsphere type. Essentially, the hydroxylated mesogenic component takes effect through changing the ratio of the liquid crystal phase, while the hydroxylated acrylate monomer can participate in the polymerization and impact the development of the polymer matrix. It is anticipated that this research can help in understanding the role of the hydroxy group in PDLC films. Full article
(This article belongs to the Section Liquid Crystals)
Show Figures

Figure 1

15 pages, 4396 KiB  
Article
From Liquid to Solid: Cocrystallization as an Engineering Tool for the Solidification of Pyruvic Acid
by Camila Caro Garrido, Koen Robeyns, Damien P. Debecker, Patricia Luis and Tom Leyssens
Crystals 2023, 13(5), 808; https://doi.org/10.3390/cryst13050808 - 12 May 2023
Viewed by 1315
Abstract
Pyruvic acid is an organic compound used in various fields (e.g., the pharmaceutical, cosmetic, food, and chemical industries) and subject to constantly growing demand. Pyruvic acid is liquid at room temperature, rendering manipulation less straightforward. Furthermore, in the liquid phase, pyruvic acid is [...] Read more.
Pyruvic acid is an organic compound used in various fields (e.g., the pharmaceutical, cosmetic, food, and chemical industries) and subject to constantly growing demand. Pyruvic acid is liquid at room temperature, rendering manipulation less straightforward. Furthermore, in the liquid phase, pyruvic acid is air-sensitive. We here present a multi-component crystal engineering strategy to render pyruvic acid solid under ambient conditions, focusing on cocrystallization and salt formation. Out of 73 screened cocrystal and salt formers, eight were found to form novel crystalline forms with pyruvic acid. Four of these were studied in detail, with pyruvic acid stable in a solid phase at temperatures up to 120 °C. These results illustrate the effectiveness of cocrystallization as a tool to convert unstable liquid compounds into stable crystalline solid forms. Full article
(This article belongs to the Special Issue Multicomponent Pharmaceutical Solids (2nd Edition))
Show Figures

Figure 1

18 pages, 3548 KiB  
Article
Carbonate Minerals’ Precipitation in the Presence of Background Electrolytes: Sr, Cs, and Li with Different Transporting Anions
by Pedro Marin-Troya, Carlos Espinosa, Luis Monasterio-Guillot and Pedro Alvarez-Lloret
Crystals 2023, 13(5), 796; https://doi.org/10.3390/cryst13050796 - 10 May 2023
Viewed by 1225
Abstract
Carbonate minerals are largely associated with many geological and biological environments as well as several industrial and technological processes. The crystalline characteristics of these mineral phases can be modified by background salts present in the solution due to the effect of different electrolytes [...] Read more.
Carbonate minerals are largely associated with many geological and biological environments as well as several industrial and technological processes. The crystalline characteristics of these mineral phases can be modified by background salts present in the solution due to the effect of different electrolytes on the dynamics of ion-water interactions and ionic strength during precipitation. In the current research, we studied the effect of the presence of several electrolytes (i.e., Cs, Li, and Sr), combined with chloride and carbonate as transporting anions, on the growth and mineral evolution processes of carbonate precipitation in solution. The electrolyte composition during the reaction (experimental times from 24 h up to 30 days) determined the formation of specific calcium carbonate polymorphs. The Li presence induced the formation of vaterite which was progressively transformed into calcite during the reaction time, while Cs stabilized the calcite formation. The Sr presence in the system caused the precipitation of strontianite with modifications in its cell parameters and the structural arrangement of the carbonate molecular group. During the mineral evolution considering chloride and carbonate experimental set-ups, several compositional and cell parameters/crystallinity variations of the carbonated phases were also observed. A better understanding of the relationship between the compositional properties of the aqueous solvent and the crystallization mechanisms can contribute to a deeper comprehension of the mineral precipitation and transformation in different multicomponent solutions that occur in natural environments and in controlled synthesis processes. Full article
(This article belongs to the Special Issue Mineralogical Crystallography (3rd Edition))
Show Figures

Figure 1

12 pages, 4796 KiB  
Article
Multichromic Behavior of Liquid Crystalline Composite Polymeric Films
by Mizuho Kondo, Satoka Yanai, Syouma Shirata, Takeshi Kakibe, Jun-ichi Nishida and Nobuhiro Kawatsuki
Crystals 2023, 13(5), 786; https://doi.org/10.3390/cryst13050786 - 09 May 2023
Viewed by 1205
Abstract
In this study, we describe the synthesis of a cholesterol-linked cyanostilobazole salt dye and the tuning of its luminescence by physical stimuli such as electricity and grinding. The dyes exhibited liquid-crystalline properties at temperatures above 170 °C. Some of the solutions were transformed [...] Read more.
In this study, we describe the synthesis of a cholesterol-linked cyanostilobazole salt dye and the tuning of its luminescence by physical stimuli such as electricity and grinding. The dyes exhibited liquid-crystalline properties at temperatures above 170 °C. Some of the solutions were transformed into orange luminescent gels upon the addition of poor solvents. When the solvent was evaporated, the resulting solid xerogel exhibited mechanochromism, its color changed, and its luminescent color changed from orange to red. Furthermore, we investigated the construction of functional gels (mechanochromic gels) that can respond to two stimuli, damage detection by abrasive responsiveness, and electrical response using ionic liquid complexes of polymers as dispersing media. This study provides a new strategy for tuning and switching luminescence using non-chemical stimuli in a single-component system using aggregation. Full article
(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan)
Show Figures

Figure 1

13 pages, 3668 KiB  
Article
Single-Crystal Growth of a Cubic Laves-Phase Ferromagnet HoAl2 by a Laser Floating-Zone Method
by Naoki Kikugawa, Takashi Kato, Momoko Hayashi and Hitoshi Yamaguchi
Crystals 2023, 13(5), 760; https://doi.org/10.3390/cryst13050760 - 03 May 2023
Cited by 1 | Viewed by 1071
Abstract
The successful growth of single crystals of a cubic Laves-phase material HoAl2 with the space group Fd-3m is reported in this study. The crystals were grown by a floating-zone method with five laser diodes as a heat source. Al-rich feed [...] Read more.
The successful growth of single crystals of a cubic Laves-phase material HoAl2 with the space group Fd-3m is reported in this study. The crystals were grown by a floating-zone method with five laser diodes as a heat source. Al-rich feed rods were prepared as compensation for heavy evaporation during the growth. The nominal ratio for the feed rods was optimized as Ho:Al = 1:2.5. Single crystals of HoAl2 with a length of 50 mm were first grown in this technique. Obtaining the large-sized crystal by the floating-zone method enabled us to systematically explore the physical properties using the same batch crystal. The crystal possessed a second-ordered ferromagnetic transition at 29 K and a first-ordered spin-reorientation transition at 20 K. The bulk physical properties, such as specific heat, magnetic susceptibility, isothermal magnetization, and thermal expansion measurements, were measured. Additionally, a magnetocaloric effect was evaluated by the magnetic entropy change. We demonstrate that anisotropic physical properties along the principal axes ([100], [110], and [111]) emerged below the magnetically ordered states, in contrast to the isotropic behavior in the paramagnetic state. Full article
(This article belongs to the Special Issue Magnetic Materials)
Show Figures

Figure 1

19 pages, 10976 KiB  
Article
Effects of Different CO2 Concentrations and Degradation Media on Static Corrosion of Commercially Pure Zinc
by Souhila Ould Mohamed, Sofia Gambaro, Ana Laura Ramirez-Ledesma, Carlo Paternoster and Diego Mantovani
Crystals 2023, 13(5), 753; https://doi.org/10.3390/cryst13050753 - 01 May 2023
Viewed by 1637
Abstract
Zn alloys have lately captivated the attention of the scientific community as possible materials for cardiovascular applications, showing a corrosion behavior and mechanical properties in between of those of Mg and Fe alloys. To better understand the different aspects of the interaction of [...] Read more.
Zn alloys have lately captivated the attention of the scientific community as possible materials for cardiovascular applications, showing a corrosion behavior and mechanical properties in between of those of Mg and Fe alloys. To better understand the different aspects of the interaction of Zn with body fluids, the basic corrosion pattern and the degradation products’ formation were investigated considering the effect of CO2 amount in the atmosphere and different pseudo-physiological media; that is Hanks’ balanced salt (HSS), Dulbecco’s phosphate-buffered saline (PSS) and physiological saline solution (NSS), through a 14-day static immersion study. A mixed degradation layer mainly composed of ZnO with Zn3(PO4)2·4H2O and Zn(CO3)2 precipitates was found on surfaces immersed in both HSS and PSS, independently of the atmosphere, while a ZnO/ZnCl2 layer was found on the surface immersed in NSS, which also revealed the higher corrosion rate due to the effect of Cl ions. Samples tested under a CO2-rich atmosphere showed a more compact passivating layer, higher dimensions crystals and less cavities when tested in HSS, PSS and NSS, respectively. Full article
(This article belongs to the Special Issue Corrosion and Oxidation of Alloys)
Show Figures

Graphical abstract

11 pages, 1538 KiB  
Article
Structure and Anharmonicity of α- and β-Sb2O3 at Low Temperature
by Duncan H. Moseley, Craig A. Bridges, Luke L. Daemen, Qiang Zhang, Michael A. McGuire, Ercan Cakmak and Raphaël P. Hermann
Crystals 2023, 13(5), 752; https://doi.org/10.3390/cryst13050752 - 01 May 2023
Viewed by 2012
Abstract
Antimony oxides are important materials for catalysis and flame-retardant applications. The two most common phases, α-Sb2O3 (senarmontite) and β-Sb2O3 (valentinite), have been studied extensively. Specific focus has been placed recently on their lattice dynamics properties [...] Read more.
Antimony oxides are important materials for catalysis and flame-retardant applications. The two most common phases, α-Sb2O3 (senarmontite) and β-Sb2O3 (valentinite), have been studied extensively. Specific focus has been placed recently on their lattice dynamics properties and how they relate to the α-β phase transformation and their potential anharmonicity. However, there has not been any direct investigation of anharmonicity in these systems, and a surprising lack of low-temperature structural information has prevented further study. Here, we report the powder neutron diffraction data of both phases of Sb2O3, as well as structural information. α-Sb2O3 behaved as expected, but β-Sb2O3 revealed a small region of zero thermal expansion along the c axis. Additionally, while the β phase matched well with reported atomic displacement parameters, the α phase displayed a marked deviation. This data will enable further investigations into these systems. Full article
(This article belongs to the Special Issue Recent Developments of Inorganic Crystalline Materials)
Show Figures

Figure 1

7 pages, 1057 KiB  
Communication
Efficient Activation and High Mobility of Ion-Implanted Silicon for Next-Generation GaN Devices
by Alan G. Jacobs, Boris N. Feigelson, Joseph A. Spencer, Marko J. Tadjer, Jennifer K. Hite, Karl D. Hobart and Travis J. Anderson
Crystals 2023, 13(5), 736; https://doi.org/10.3390/cryst13050736 - 27 Apr 2023
Cited by 1 | Viewed by 1313
Abstract
Selective area doping via ion implantation is crucial to the implementation of most modern devices and the provision of reasonable device design latitude for optimization. Herein, we report highly effective silicon ion implant activation in GaN via Symmetrical Multicycle Rapid Thermal Annealing (SMRTA) [...] Read more.
Selective area doping via ion implantation is crucial to the implementation of most modern devices and the provision of reasonable device design latitude for optimization. Herein, we report highly effective silicon ion implant activation in GaN via Symmetrical Multicycle Rapid Thermal Annealing (SMRTA) at peak temperatures of 1450 to 1530 °C, producing a mobility of up to 137 cm2/Vs at 300K with a 57% activation efficiency for a 300 nm thick 1 × 1019 cm−3 box implant profile. Doping activation efficiency and mobility improved alongside peak annealing temperature, while the deleterious degradation of the as-grown material electrical properties was only evident at the highest temperatures. This demonstrates efficient dopant activation while simultaneously maintaining low levels of unintentional doping and thus a high blocking voltage potential of the drift layers for high-voltage, high-power devices. Furthermore, efficient activation with high mobility has been achieved with GaN on sapphire, which is known for having relatively high defect densities but also for offering significant commercial potential due to the availability of cheap, large-area, and robust substrates for devices. Full article
(This article belongs to the Special Issue Research in GaN-based Materials and Devices)
Show Figures

Figure 1

11 pages, 2992 KiB  
Article
Strain-Induced Band Gap Variation in InGaN/GaN Short Period Superlattices
by Polyxeni Chatzopoulou, Isaak G. Vasileiadis, Philomela Komninou, Vassilis Pontikis, Theodoros Karakostas and George P. Dimitrakopulos
Crystals 2023, 13(4), 700; https://doi.org/10.3390/cryst13040700 - 19 Apr 2023
Cited by 2 | Viewed by 1594
Abstract
The use of strained substrates may overcome indium incorporation limits without inducing plastic relaxation in InGaN quantum wells, and this is particularly important for short-period InGaN/GaN superlattices. By incorporating elastic strain into these heterostructures, their optoelectronic behavior is modified. Our study employed density [...] Read more.
The use of strained substrates may overcome indium incorporation limits without inducing plastic relaxation in InGaN quantum wells, and this is particularly important for short-period InGaN/GaN superlattices. By incorporating elastic strain into these heterostructures, their optoelectronic behavior is modified. Our study employed density functional theory calculations to investigate the variation in the band-gap energy of short-period InGaN/GaN superlattices that comprise pseudomorphic quantum wells with a thickness of just one monolayer. Heterostructures with equibiaxially strained GaN barriers were compared with respective ones with relaxed barriers. The findings reveal a reduction of the band gap for lower indium contents, which is attributed to the influence of the highly strained nitrogen sublattice. However, above mid-range indium compositions, the situation is reversed, and the band gap increases with the indium content. This phenomenon is attributed to the reduction of the compressive strain in the quantum wells caused by the tensile strain of the barriers. Our study also considered local indium clustering induced by phase separation as another possible modifier of the band gap. However, unlike the substrate-controlled strain, this was not found to exert a significant influence on the band gap. Overall, this study provides important insights into the behavior of the band-gap energy of strained superlattices toward optimizing the performance of optoelectronic devices based on InGaN/GaN heterostructures. Full article
(This article belongs to the Special Issue Group-III Nitride Quantum Wells)
Show Figures

Figure 1

15 pages, 31035 KiB  
Article
Spectroscopic Properties of Pb2+-Doped BaF2 Crystals
by Gabriel Buse, Marius Stef and Irina Nicoara
Crystals 2023, 13(4), 659; https://doi.org/10.3390/cryst13040659 - 11 Apr 2023
Cited by 1 | Viewed by 1064
Abstract
Various concentrations of PbF2-doped BaF2 crystals were grown by the Bridgman method using a shaped graphite heater. The room temperature optical absorption spectra showed two UV absorption bands (labeled A and D), characteristic of the Pb2+ ions. The structure [...] Read more.
Various concentrations of PbF2-doped BaF2 crystals were grown by the Bridgman method using a shaped graphite heater. The room temperature optical absorption spectra showed two UV absorption bands (labeled A and D), characteristic of the Pb2+ ions. The structure of the bands was analyzed using the Gaussian multi-peak fitting. The distribution of the Pb2+ ions along the crystals and the effective segregation coefficient were studied using the optical absorption method. The obtained effective segregation coefficient was >1. The Pb2+ ions were not uniformly distributed along the samples. High intensity emission bands were observed in the near UV domain and the visible region. Full article
(This article belongs to the Special Issue Advances in Crystals for Optoelectronics)
Show Figures

Figure 1