Crystals

Open AccessArticle

Microstructural Evolution and Deterioration of Shear Properties of Sn3.0Ag0.5Cu/Cu Solder Joints after Long-Term Storage at Cryogenic Temperatures

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Crystals 2023, 13(4), 586; https://doi.org/10.3390/cryst13040586 (registering DOI) - 29 Mar 2023

Abstract

In deep space exploration the exploration equipment will inevitably experience the harsh environment of cryogenic temperature. Solder joints belong to the most vulnerable parts of electronic equipment, and the harsh environment of extreme cryogenic temperature will seriously threaten the reliability of solder joints. [...] Read more.

In deep space exploration the exploration equipment will inevitably experience the harsh environment of cryogenic temperature. Solder joints belong to the most vulnerable parts of electronic equipment, and the harsh environment of extreme cryogenic temperature will seriously threaten the reliability of solder joints. In this paper, Sn3.0Ag0.5Cu/Cu solder joints were prepared and stored at cryogenic temperatures (−50 °C, −100 °C, and −196 °C) for up to 960 h, whilst studying the microstructural evolution and deterioration of shear properties. The results showed that the influence of cryogenic temperature on microstructure deterioration was greater than that of storage time. With the decrease of storage temperature and the extension of storage time, the Ag₃Sn intermetallic compounds (IMCs) were uniformly dispersed in the β-Sn matrix; the size decreased and the number increased. After being stored at −196 °C for 960 h, some microcracks appeared at the interface of the solder joints. Meanwhile, the shear force of the solder joints was reduced by 19.02%, and the fracture mode changed from ductile fracture to ductile–brittle mixed fracture. Therefore, it is of great scientific significance to reveal the microstructural evolution and deterioration of shear properties of the solder joints under long-term storage at cryogenic temperatures. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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Open AccessArticle

The Effect of Interatomic Potentials on the Nature of Nanohole Propagation in Single-Crystal Nickel: A Molecular Dynamics Simulation Study

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Crystals 2023, 13(4), 585; https://doi.org/10.3390/cryst13040585 - 29 Mar 2023

Abstract

Based on a molecular dynamics (MD) simulation, we investigated the nanohole propagation behaviors of single-crystal nickel (Ni) under different styles of Ni–Ni interatomic potentials. The results show that the MEAM (the modified embedded atom method potential) potential is best suited to describe the [...] Read more.

Based on a molecular dynamics (MD) simulation, we investigated the nanohole propagation behaviors of single-crystal nickel (Ni) under different styles of Ni–Ni interatomic potentials. The results show that the MEAM (the modified embedded atom method potential) potential is best suited to describe the brittle propagation behavior of nanoholes in single-crystal Ni. The EAM/FS (embedded atom method potential developed by Finnis and Sinclair) potential, meanwhile, is effective at characterizing the plastic growth behavior of nanoholes in single-crystal Ni. Furthermore, the results show the difference between the different styles of interatomic potentials in characterizing nanohole propagation in single-crystal Ni and provide a theoretical basis for the selection of interatomic potentials in the MD simulation of Ni crystals. Full article

(This article belongs to the Special Issue Crystallization of High Performance Metallic Materials)

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Open AccessArticle

Effects of Crack Formation on the Mechanical Properties of Bilayer Graphene: A Comparative Analysis

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Crystals 2023, 13(4), 584; https://doi.org/10.3390/cryst13040584 - 29 Mar 2023

Abstract

We present a molecular dynamics simulation study on the effects of crack formation on the mechanical properties of bilayer graphene. Bilayer graphene possesses unique electronic properties that can be modified by applying a voltage, making it an attractive material for various applications. We [...] Read more.

We present a molecular dynamics simulation study on the effects of crack formation on the mechanical properties of bilayer graphene. Bilayer graphene possesses unique electronic properties that can be modified by applying a voltage, making it an attractive material for various applications. We examined how the mechanical properties of bilayer graphene vary under various crack configurations and temperatures, measuring Young’s modulus, fracture toughness, fracture strain, and fracture stress. We compared the effect of crack presence on single and both layers and found the appearance of double peaks in the stress–strain curves in the case of a monolayer crack, indicating a subsequent fracture of the cracked layer and the uncracked layer. We also examined the effect of crack shape, size, and orientation on mechanical properties, including circular, hexagonal, and rectangular cracks along two axes. We found that both circular and hexagonal cracks had a smaller Young’s modulus and toughness than rectangular cracks, and the orientation of the crack had a significant impact on the mechanical properties, with a 2.5-times higher toughness for cracks with a length of 15

Å

. Additionally, we found that Young’s modulus decreases with increasing temperature in bilayer graphene with cracks on both layers. Our findings provide valuable insights into the potential applications of bilayer graphene in the design of advanced nanoscale electronic devices. Full article

(This article belongs to the Special Issue Graphene Mechanics Volume III)

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Open AccessArticle

Neuro-Evolutive Modeling of Transition Temperatures for Five-Ring Bent-Core Molecules Derived from Resorcinol

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Elena Niculina Drăgoi

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Crystals 2023, 13(4), 583; https://doi.org/10.3390/cryst13040583 - 29 Mar 2023

Abstract

Determining the phase transition temperature of different types of liquid crystals based on their structural parameters is a complex problem. The experimental work might be eliminated or reduced if prediction strategies could effectively anticipate the behavior of liquid crystalline systems. Neuro-evolutive modeling based [...] Read more.

Determining the phase transition temperature of different types of liquid crystals based on their structural parameters is a complex problem. The experimental work might be eliminated or reduced if prediction strategies could effectively anticipate the behavior of liquid crystalline systems. Neuro-evolutive modeling based on artificial neural networks (ANN) and a differential evolution (DE) algorithm was applied to predict the phase transition temperatures of bent-core molecules based on their resorcinol core. By these means, structural parameters such as the nature of the linking groups, the position, size and number of lateral substituents on the central core or calamitic wings and the length of the terminal chains were taken into account as factors that influence the liquid crystalline properties. A number of 172 bent-core compounds with symmetrical calamitic wings were selected from the literature. All corresponding structures were fully optimized using the DFT, and the molecular descriptors were calculated afterward. In the first step, the ANN-DE approach predicted the mesophase presence for the analyzed compounds. Next, ANN models were determined to predict the transition temperatures and whether or not the bent-core compounds were mesogenic. Simple structural, thermophysical and electronic structure descriptors were considered as inputs in the dataset. As a result, the models determined for each individual temperature have an R² that varied from 0.89 to 0.98, indicating their capability to estimate the transition temperatures for the selected compounds. Moreover, the impact analysis of the inputs on the predicted temperatures showed that, in most cases, the presence or not of liquid crystalline properties represents the most influential feature. Full article

(This article belongs to the Special Issue Synthesis of Liquid Crystals and Cellulose Derivatives Liquid Crystalline Phases: Recent Advances)

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Open AccessArticle

Microstructure and Mechanical Property Evolution of Robotic Friction Stir-Welded Al–Li Alloys

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Crystals 2023, 13(4), 582; https://doi.org/10.3390/cryst13040582 - 29 Mar 2023

Abstract

2198 aluminum–lithium alloy was friction stir-welded with a KUKA Robot integrated with a compact friction stir-welding head with a rotation speed of 800 rpm at different welding speeds. The real-time tool force in the three directions of Fx, Fy and Fz was measured [...] Read more.

2198 aluminum–lithium alloy was friction stir-welded with a KUKA Robot integrated with a compact friction stir-welding head with a rotation speed of 800 rpm at different welding speeds. The real-time tool force in the three directions of Fx, Fy and Fz was measured with a load sensor. Mechanical properties and microstructure evolution were investigated systematically. The results showed that Fz force increased from 3.2 kN to 8.5 kN as welding speed increased from 50 mm/min to 500 mm/min. Ultimate tensile strength of 383 MPa, 88% of base metal, was obtained when the welding speed was 100 mm/min. The nugget zone consisted of refined grains with an average size of 4 μm. TEM investigation demonstrates that T1 precipitation predominated in the base metal and disappeared in the nugget zone, as a small amount of δ’ was retained. The W-shape hardness profile in all weldments and higher welding speed lead to a higher hardness value. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals Welding Joints)

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Open AccessArticle

Effect of Aging State on the Microstructure and Tensile Properties of Al-7.0Zn-2.5Mg-2.0Cu-0.1Zr-0.2Sc Alloy

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Crystals 2023, 13(4), 581; https://doi.org/10.3390/cryst13040581 - 28 Mar 2023

Abstract

Tensile experiments were conducted for Al-7.0Zn-2.5Mg-2.0Cu-0.1Zr-0.2Sc alloy in different aging states (18 h, 24 h, 36 h) with temperature environments including room temperature, −10 °C and −30 °C. Comparative studies were made on the evolution of the precipitate phase in alloys at three [...] Read more.

Tensile experiments were conducted for Al-7.0Zn-2.5Mg-2.0Cu-0.1Zr-0.2Sc alloy in different aging states (18 h, 24 h, 36 h) with temperature environments including room temperature, −10 °C and −30 °C. Comparative studies were made on the evolution of the precipitate phase in alloys at three kinds of aging times and the evolution of tensile properties in alloys under different ambient temperatures. The findings showed that the precipitates in Al-7.0Zn-2.5Mg-2.0Cu-0.1Zr-0.2Sc alloy were mainly in the GP zone after the solution + aging treatment η’ phase, the secondary Al₃ (Sc, Zr) phase and the θ’ (Al₂Cu) phase. As the aging time was prolonged, the η’ phase gradually grew and the PFZ gradually widened. At the three test temperatures, the tensile strength (TS) and yield strength (YS) of the alloys both showed a trend of first increasing before decreasing with the extension of aging time, while the elongation (A) and section shrinkage (Z) showed a decreasing trend. As the test temperature decreased, the TS and YS of the alloys increased and the A and Z of the alloys decreased. At room temperature, alloys showed a ductile fracture mode, which changed to mixed ductile and brittle fracture with decreasing test temperature. Full article

(This article belongs to the Special Issue Feature Papers in Crystalline Metals and Alloys in 2022-2023)

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Open AccessArticle

Preparation of HfNbTiTaZr Thin Films by Ionized Jet Deposition Method

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Crystals 2023, 13(4), 580; https://doi.org/10.3390/cryst13040580 - 28 Mar 2023

Abstract

The ionized jet deposition (IJD) method is applied to the preparation of thin films composed of refractory HfNbTiTaZr high-entropy alloy (HEA). Due to its stoichiometric reliability, the IJD method provides a flexible tool for deposition of complex multi-element materials, such as HEAs. Scanning [...] Read more.

The ionized jet deposition (IJD) method is applied to the preparation of thin films composed of refractory HfNbTiTaZr high-entropy alloy (HEA). Due to its stoichiometric reliability, the IJD method provides a flexible tool for deposition of complex multi-element materials, such as HEAs. Scanning electron microscopy, energy-dispersion spectroscopy, confocal microscopy, and X-ray diffraction methods are used to characterize the influence of the applied accelerating voltage of the IJD deposition head ranging from 16 to 22 kV on the resulting morphology, chemical composition, thickness, crystalline structure, and phase composition of the layers prepared as 10 mm-wide strips on a single stainless-steel substrate. With a low accelerating voltage applied, the best surface homogeneity is obtained. Transfer coefficient values characterizing the elemental transport between the bulk target and the grown layer are evaluated for each constituting element and applied voltage. With the IJD accelerating voltage approaching 22 kV, the coefficients converge upon the values proportional to the atomic number of the element. Such voltage dependence of the IJD elemental transport might be used as a suitable tool for fine-tuning the elemental composition of layers grown from a single deposition target. Full article

(This article belongs to the Special Issue Fabrication, Structures and Properties of High Entropy Alloys and Refractory High Entropy Alloys)

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Open AccessArticle

Hydroxyapatite-Barium Titanate Biocoatings Using Room Temperature Coblasting

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Crystals 2023, 13(4), 579; https://doi.org/10.3390/cryst13040579 - 28 Mar 2023

Abstract

The use of orthopaedic and dental implants is expanding as a consequence of an ageing population and also due to illness or trauma in younger age groups. The implant must be biocompatible, bioactive and interact favourably with the recipient’s bone, as rapid osseointegration [...] Read more.

The use of orthopaedic and dental implants is expanding as a consequence of an ageing population and also due to illness or trauma in younger age groups. The implant must be biocompatible, bioactive and interact favourably with the recipient’s bone, as rapid osseointegration is key to success. In this work, Ti-6Al-4V plates were coated using the CoBlast^TM technique, with hydroxyapatite (HAp) and HAp/BaTiO₃ (barium titanate, BT) non-piezoelectric cubic nanopowders (HAp/cBT) and piezoelectric tetragonal micropowders (HAp/tBT). The addition of BT, a piezoelectric ceramic, is a strategy to accelerate osseointegration by using surface electric charges as cues for cells. For comparison with commercial coatings, plates were coated with HAp using the plasma spray technique. Using XRD and FTIR, both plasma spray and CoBlast^TM coatings showed crystalline HAp and no presence of by-products. However, the XRD of the plasma-sprayed coatings revealed the presence of amorphous HAp. The average surface roughness was close to the coatings’ thickness (≈5 μm for CoBlast^TM and ≈13 μm for plasma spray). Cytotoxicity assays proved that the coatings are biocompatible. Therefore, it can be concluded that for HAp-based coatings, CoBlast^TM is a viable alternative to plasma spray, with the advantage of facilitating room temperature addition of other ceramics, like piezoelectric BaTiO₃. Full article

(This article belongs to the Special Issue Advances in New Functional Biomaterials for Medical Applications)

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Open AccessArticle

Epitaxial Integration of Dirac Semimetals with Si(001)

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Anthony Rice

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Kirstin Alberi

Crystals 2023, 13(4), 578; https://doi.org/10.3390/cryst13040578 - 28 Mar 2023

Abstract

Topological semimetals contain novel combinations of properties that make them useful in a variety of applications, including optoelectronics, spintronics and low energy computing, and catalysis. Although they have been grown with high quality as bulk single crystals, incorporation with semiconductor substrates will ultimately [...] Read more.

Topological semimetals contain novel combinations of properties that make them useful in a variety of applications, including optoelectronics, spintronics and low energy computing, and catalysis. Although they have been grown with high quality as bulk single crystals, incorporation with semiconductor substrates will ultimately be required to maximize their technological reach. Here, epitaxial growth of the Dirac semimetal Cd

_{3}

As

_{2}

on Si(001) is demonstrated through two routes. First, Cd

_{3}

As

_{2}

(112) epilayers are grown on Si(001) via an intermediate CdTe(111) buffer layer. Second, Cd

_{3}

As

_{2}

(112) is grown directly on Si(001). This work sets the foundation for integration of novel semimetal materials with existing CMOS technology. Full article

(This article belongs to the Special Issue Epitaxial Growth of Semiconductor Materials and Devices)

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Open AccessArticle

Photocatalytic Azo Dye Degradation Using Graphite Carbon Nitride Photocatalyst and UV-A Irradiation

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Salma A. Al-Zahrani

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Mallikarjunagouda B. Patil

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Crystals 2023, 13(4), 577; https://doi.org/10.3390/cryst13040577 - 28 Mar 2023

Abstract

The photocatalytic degradation of Acid Red 26 was examined utilizing a graphitic carbon nitride (g-C₃N₄) catalyst and a UV-A light in this study. We investigated how successfully the photocatalytic approach removed Acid Red 26 from synthetic and actual municipal [...] Read more.

The photocatalytic degradation of Acid Red 26 was examined utilizing a graphitic carbon nitride (g-C₃N₄) catalyst and a UV-A light in this study. We investigated how successfully the photocatalytic approach removed Acid Red 26 from synthetic and actual municipal wastewater. Both aqueous matrices allowed for extremely high clearance rates. Wastewater degraded at a slower rate than the other matrices, this might be ascribed to the wastewater’s complicated chemical composition. Using a liquid chromatography-mass spectrometry (LC-MS), the IPs in both synthetic and actual municipal effluent were determined. The photocatalytic degradation mechanisms of Acid Red 26 are hypothesised to comprise oxidation, dealkylation, and methoxy group cleavage based on the observed intermediate products (IPs). Using proven scavengers, we were also able to investigate the role of reactive species in the degradation process and illustrate the significance of h⁺ and O₂^• in the reaction. Chlorococcum sp. and Dunaliella tertiolecta microalgae were also utilised to assess the development of ecotoxicity. We observed low toxicity throughout the process when clean water was used as the matrix, with no production of hazardous IPs. In the case of actual municipal wastewater, there was an early rise in toxicity, which scientists believe was caused by the matrix’s chemical make-up. To lower the toxicity, a heterogeneous photocatalysis was used, and at the end of the treatment, nearly full detoxification was obtained. Full article

(This article belongs to the Special Issue Recent Developments of Inorganic Crystalline Materials)

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Open AccessReview

Friction Stir Welding of Non-Heat Treatable Al Alloys: Challenges and Improvements Opportunities

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Behrouz Abnar

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Samaneh Gashtiazar

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Mousa Javidani

Crystals 2023, 13(4), 576; https://doi.org/10.3390/cryst13040576 - 28 Mar 2023

Abstract

Friction stir welding (FSW) is an effective solid-state joining process that has the potential to overcome common problems correlated with conventional fusion welding processes. FSW is used for the joining of metallic materials, in particular Al alloys (non-heat-treatable and heat-treatable). The heat produced [...] Read more.

Friction stir welding (FSW) is an effective solid-state joining process that has the potential to overcome common problems correlated with conventional fusion welding processes. FSW is used for the joining of metallic materials, in particular Al alloys (non-heat-treatable and heat-treatable). The heat produced by the friction between the rotating tool and the workpiece material generates a softened region near the FSW tool. Although the heat input plays a crucial role in producing a defect-free weld metal, it is a serious concern in the FSW of work-hardened non-heat-treatable Al alloys. In this group of alloys, the mechanical properties, including hardness, tensile properties, and fatigue life, are adversely affected by the softening effect because of grain growth and reduced dislocation density. Considering this challenge, work-hardened Al alloys have been limited in their industrial use, which includes aerospace, shipbuilding, automotive, and railway industries. The current comprehensive review presents the various approaches of available studies for improving the quality of FSW joints and expanding their use. First, the optimization of welding parameters, including the tool rotational and traverse speeds, tool design, plunge depth, and the tilt angle is discussed. Second, the incorporation of reinforcement particles and then underwater FSW are stated as other effective strategies to strengthen the joint. Finally, some supplementary techniques containing surface modification, bobbin tool FSW, copper backing, and double-sided FSW in relation to strain-hardened Al alloys are considered. Full article

(This article belongs to the Special Issue Metals Manufacturing Techniques: Processing, Microstructure and Properties)

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Open AccessArticle

Spectroscopic Characteristics and Coloring Mechanisms of Different Colored Spinels from Myanmar

by

Lei Zhang

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Kui He

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Qingfeng Guo

Crystals 2023, 13(4), 575; https://doi.org/10.3390/cryst13040575 - 28 Mar 2023

Abstract

Spinel is a common gemstone that has attracted the attention of gemologists worldwide because of its high refractive index, rich colors and brilliant hues. Myanmar is an important source of spinel. The present paper provides a systematic characterization of the gemological features of [...] Read more.

Spinel is a common gemstone that has attracted the attention of gemologists worldwide because of its high refractive index, rich colors and brilliant hues. Myanmar is an important source of spinel. The present paper provides a systematic characterization of the gemological features of different color spinels from Myanmar, with a discussion and analysis of their color causes. The results show that complete octahedral crystal forms can be seen in Myanmar spinel, with the appearance of dissolution, growth motifs and cross-growth of crystals visible on the crystal surfaces. The XRF results show that the Myanmar red and orange spinel samples contain high levels of Cr, with the magenta sample having significant levels of Cr and the orange sample having more V. The blue and purple samples have high levels of Fe. The peaks of the infrared spectrum mainly appear around 841 cm⁻¹, 690 cm⁻¹ and 532 cm⁻¹. Raman spectra have peaks mainly around 310 cm⁻¹, 405 cm⁻¹, 663 cm⁻¹ and 764 cm⁻¹. According to the UV-Vis spectrum, the color of Myanmar red and orange spinels is mainly due to Cr³⁺ and V³⁺. When the Cr³⁺ content is higher than the V³⁺ content, the spinels show a red hue; when the V³⁺ content is higher than Cr³⁺, the spinels have an orange hue. Blue color is due to the charge transfer between Fe²⁺ and Fe³⁺. The research in this paper has enriched the gemological characteristics of Myanmar spinel and can provide a theoretical basis for its investigation, marketability, design and utilization. Full article

(This article belongs to the Special Issue New Trends in Gemstones and Jades at China University of Geosciences, Beijing)

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Open AccessArticle

Oxygen Vacancies in Zirconia and Their Migration: The Role of Hubbard-U Parameters in Density Functional Theory

by

Ralph Gebauer

Crystals 2023, 13(4), 574; https://doi.org/10.3390/cryst13040574 - 28 Mar 2023

Abstract

Cubic zirconia (c-ZrO

_{2}

) is studied using Density Functional Theory with Hubbard-U corrections (DFT+U). It is shown that the determination of the U-parameters from first principles leads to values for U(Zr-4d) and U(O-2p) which are very different from standard [...] Read more.

Cubic zirconia (c-ZrO

_{2}

) is studied using Density Functional Theory with Hubbard-U corrections (DFT+U). It is shown that the determination of the U-parameters from first principles leads to values for U(Zr-4d) and U(O-2p) which are very different from standard choices. The calculated band gap with these values for U closely matches the experimental gap. Oxygen vacancies are studied using this approach, and it is found that it is possible to closely reproduce the vacancy migration energies calculated with a hybrid functional. The oxygen vacancy is associated with two excess electrons which localize in the vacancy’s cavity. In the presence of these excess electrons, the barrier for vacancy migration is very high. If instead, a charged vacancy V

_{O}

^{2 +}

is considered, its mobility increases considerably—an effect that is attributed to the absence of space charges localized in the cavity. Full article

(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)

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Open AccessArticle

Magnetic Field-Dependent Microstructure Evolution of Solidified Co_39.2Ni_39.2Al_21.6 Eutectic Medium-Entropy Alloy

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Crystals 2023, 13(4), 573; https://doi.org/10.3390/cryst13040573 - 28 Mar 2023

Abstract

A (Fe, Cr)-free Co_39.2Ni_39.2Al_21.6 eutectic medium-entropy alloy (EMEA) was designed and fabricated to study the microstructure and its evolution during slow solidification under different intensities of high static magnetic field (0 T, 5 T and 10 T). It [...] Read more.

A (Fe, Cr)-free Co_39.2Ni_39.2Al_21.6 eutectic medium-entropy alloy (EMEA) was designed and fabricated to study the microstructure and its evolution during slow solidification under different intensities of high static magnetic field (0 T, 5 T and 10 T). It was found that the original microstructure was characterized by FCC/BCC mixed herringbone eutectics consisting of two types of lamellar structures: a curved and wormy anomalous eutectic in the fringe, and a straight and long regular eutectic in the center. Nano-sized L1₀-type martensite layers are also distributed on the BCC lamellar as the martensitic transformation product. The FCC and BCC phases were enriched in Co and Al elements, respectively, while Ni element was distributed homogenously in both phases. With increasing magnetic field intensity, the herringbone eutectic structures remained stable, without the formation of a primary phase, while the phase constitution and the orientation relationships in the eutectic structures remained unchanged, with no obvious magnetically induced alignments. However, the lamellar spacing of the regular lamellar eutectic decreased significantly from 3.3 μm (0 T) to 1.93 μm (10 T); by contrast, the volume fraction of the anomalous eutectics increased considerably from 28.35% (0 T) to 55.14% (10 T), and the assumption that the imposed convection and destabilization of lamellar eutectics is controlled by the magnetic field is discussed in depth. Our results show a great potential for tailoring microstructures and properties by applying a strong magnetic field during the solidification process of EMEAs. Full article

(This article belongs to the Special Issue Recently Research on Eutectic Alloy Materials)

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Open AccessCommunication

Optoelectronic Simulations of InGaN-Based Green Micro-Resonant Cavity Light-Emitting Diodes with Staggered Multiple Quantum Wells

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Crystals 2023, 13(4), 572; https://doi.org/10.3390/cryst13040572 (registering DOI) - 27 Mar 2023

Abstract

In this research, we compared the performance of commercial μ-LEDs and three-layered staggered QW μ-LED arrays. We also investigated the self-heating effect. We proposed a green micro-resonant cavity light-emitting diode (µ-RCLED) that consists of a three-layer staggered InGaN with multiple quantum wells (MQWs), [...] Read more.

In this research, we compared the performance of commercial μ-LEDs and three-layered staggered QW μ-LED arrays. We also investigated the self-heating effect. We proposed a green micro-resonant cavity light-emitting diode (µ-RCLED) that consists of a three-layer staggered InGaN with multiple quantum wells (MQWs), a bottom layer of nanoporous n-GaN distributed Bragg reflectors (DBRs), and a top layer of Ta₂O₅/SiO₂ DBRs. We systematically performed simulations of the proposed µ-RCLEDs. For the InGaN MQWs with an input current of 300 mA, the calculated wavefunction overlaps are 8.8% and 18.1% for the regular and staggered structures, respectively. Furthermore, the staggered MQWs can reduce the blue-shift of electroluminescence from 10.25 nm, obtained with regular MQWs, to 2.25 nm. Due to less blue-shift, the output power can be maintained even at a high input current. Conversely, by employing 6.5 pairs of Ta₂O₅/SiO₂ DBRs stacks, the full width at half maximum (FWHM) can be significantly reduced from 40 nm, obtained with ordinary µ-LEDs, to 0.3 nm, and a divergence angle smaller than 60° can be obtained. Our simulation results suggest that the µ-RCLEDs can effectively resolve the wavelength instability and color purity issues of conventional µ-LEDs. Full article

(This article belongs to the Special Issue III-Nitride-Based Light-Emitting Devices)

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Open AccessArticle

Laser Damage Performance Study of Fundamental Frequency Dielectric Film Optical Elements

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Crystals 2023, 13(4), 571; https://doi.org/10.3390/cryst13040571 - 27 Mar 2023

Abstract

In laser application systems, the optical film is one of the most important parts of the system, as well as its weakest link. Its damage performance determines the output characteristics and safety performance of the laser system. This paper focuses on the fundamental [...] Read more.

In laser application systems, the optical film is one of the most important parts of the system, as well as its weakest link. Its damage performance determines the output characteristics and safety performance of the laser system. This paper focuses on the fundamental frequency reflection of dielectric films used in large high-powered laser devices. The study of the dielectric film’s initial laser damage performance and laser damage growth performance is carried out through laser damage testing and microscopic morphology testing of the damage. The results show two different damage morphologies: type 1 damage (film discoloration damage) and type 2 damage (cratered damage), and the damage growth behavior between the two is very different, with type 1 damage not growing and type 2 damage growing rapidly under subsequent episodes that trigger their damage fluxes. The difference in the growth behavior is well explained by the micro-zone surface shape of the damage location. The results of this paper help to deepen the understanding of the dielectric membrane element processing process and the damage growth behavior. Full article

(This article belongs to the Special Issue Laser-Induced Damage Properties of Optical Materials)

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Open AccessEditorial

Multicomponent Pharmaceutical Solids

by

Duane Choquesillo-Lazarte

and

Alicia Domínguez-Martín

Crystals 2023, 13(4), 570; https://doi.org/10.3390/cryst13040570 - 27 Mar 2023

Abstract

Multicomponent pharmaceutical solids is a hot topic that brings together the knowledge of crystal engineering and the need to achieve novel and effective drugs at lower costs for the pharmaceutical industry [...] Full article

(This article belongs to the Special Issue Multicomponent Pharmaceutical Solids)

Open AccessArticle

Supramolecular Structure of Tris(1,10-phenanthroline)zinc(II)-Cation and N,N′,N″-tris(carboxymethyl)-1,3,5-benzenetricarboxamide-Anion: Synthesis, Crystal Structure, Vibrational Spectra, and Theoretical Investigations

by

Niels-Patrick Pook

Crystals 2023, 13(4), 569; https://doi.org/10.3390/cryst13040569 - 27 Mar 2023

Abstract

The present work reports on the synthesis, structural, spectroscopic, and theoretical studies of a new solid state ionic compound mainly composed of tris(1,10-phenanthroline)zinc(II) cations and N,N′,N″-tris(carboxymethyl)-1,3,5-benzenetricarboxamide anions. Colorless and well-shaped crystals were obtained from an alkaline aqueous methanolic solution, and single-crystal X-ray diffraction [...] Read more.

The present work reports on the synthesis, structural, spectroscopic, and theoretical studies of a new solid state ionic compound mainly composed of tris(1,10-phenanthroline)zinc(II) cations and N,N′,N″-tris(carboxymethyl)-1,3,5-benzenetricarboxamide anions. Colorless and well-shaped crystals were obtained from an alkaline aqueous methanolic solution, and single-crystal X-ray diffraction revealed a distinct supramolecular network. Powder diffraction techniques and Rietveld analysis confirmed the phase purity of the crystalline probes. The compound crystallizes in the orthorhombic space group Pbca with a cell volume of 9517.0 Å³. The complex cations [Zn(phen)₃]²⁺ are interconnected via π–π-interactions and form a cationic layer network with holes. The organic counterion, as a dianion, forms dimeric units through π–π-interactions and hydrogen bonds, which also form an anionic layer network with honeycomb-like holes through cooperative classical hydrogen bonds of the O∙∙∙H–O and O∙∙∙H–N type with attractive secondary electrostatic interactions. Using the holes, the resulting supramolecular framework can be described as an interpenetrated network of separate anionic and cationic layers linked by further weaker non-covalent interactions such as C–H∙∙∙π and lone-pair∙∙∙π interactions. DFT calculations confirmed the experimentally observed spectroscopic (IR and Raman) findings. For a deeper insight into the structural arrangement in the crystal, the different Hirshfeld surfaces of the cation and anion, the pairwise interaction energies as well as the energy framework were calculated, supporting the dominance of attractive and repulsive electrostatic forces between the ions. Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds (Volume II))

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Open AccessArticle

Design of Titanium Alloys Insensitive to Thermal History for Additive Manufacturing

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Crystals 2023, 13(4), 568; https://doi.org/10.3390/cryst13040568 - 27 Mar 2023

Abstract

Powder bed fusion is the most common technology used for 3D printing, where thermal energy is used to selectively melt/sinter granular materials into solid shapes. The build platform is then lowered, more powder is added, and the process is repeated for the next [...] Read more.

Powder bed fusion is the most common technology used for 3D printing, where thermal energy is used to selectively melt/sinter granular materials into solid shapes. The build platform is then lowered, more powder is added, and the process is repeated for the next layer to fully print the design. As a result, the built-up part is repeatedly heated. Therefore, materials that are not sensitive to thermal history are preferred for this process. The Ti–Zr system forms a continuous solid solution for both β- and α-phases. The presence of Fe in Ti alloys is inevitable; however, it provides some beneficial effects. The purpose of this work was to prepare Ti–Zr–Fe alloys and investigate their heat treatment behaviour. Ti-xmass%Zr-1mass%Fe alloys (x = 0, 5, 10) were prepared with arc melting. The formation of a solid solution of Zr in Ti was confirmed on the basis of X-ray diffraction peak shifts and hardening effects. A small amount of β-phase precipitation was suggested by the change in electrical resistivity after isothermal ageing at 673 and 773 K. However, no obvious phase or microstructural changes were observed. The laser scanning increased the volume of the precipitates and also coarsened them, but the effect was limited. Full article

(This article belongs to the Special Issue Anisotropic/ Isotropic Microstructural Design in Additive Manufacturing)

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