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12 pages, 4477 KiB

Open AccessArticle

Investigation of Electrochromic, Combinatorial TiO₂-SnO₂ Mixed Layers by Spectroscopic Ellipsometry Using Different Optical Models

by Noor Taha Ismaeel, Zoltán Lábadi, Peter Petrik and Miklós Fried

Materials 2023, 16(12), 4204; https://doi.org/10.3390/ma16124204 - 06 Jun 2023

Viewed by 983

Abstract

We determined the optimal composition of reactive magnetron-sputtered mixed layers of Titanium oxide and Tin oxide (TiO₂-SnO₂) for electrochromic purposes. We determined and mapped the composition and optical parameters using Spectroscopic Ellipsometry (SE). Ti and Sn targets were put [...] Read more.

We determined the optimal composition of reactive magnetron-sputtered mixed layers of Titanium oxide and Tin oxide (TiO₂-SnO₂) for electrochromic purposes. We determined and mapped the composition and optical parameters using Spectroscopic Ellipsometry (SE). Ti and Sn targets were put separately from each other, and the Si-wafers on a glass substrate (30 cm × 30 cm) were moved under the two separated targets (Ti and Sn) in a reactive Argon-Oxygen (Ar-O₂) gas mixture. Different optical models, such as the Bruggeman Effective Medium Approximation (BEMA) or the 2-Tauc–Lorentz multiple oscillator model (2T–L), were used to obtain the thickness and composition maps of the sample. Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDS) has been used to check the SE results. The performance of diverse optical models has been compared. We show that in the case of molecular-level mixed layers, 2T–L is better than EMA. The electrochromic effectiveness (the change of light absorption for the same electric charge) of mixed metal oxides (TiO₂-SnO₂) that are deposited by reactive sputtering has been mapped too. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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10 pages, 3360 KiB

Open AccessEditor’s ChoiceArticle

Ferroelectricity and Oxide Reliability of Stacked Hafnium–Zirconium Oxide Devices

by Ruo-Yin Liao, Hsuan-Han Chen, Ping-Yu Lin, Ting-An Liang, Kuan-Hung Su, I-Cheng Lin, Chen-Hao Wen, Wu-Ching Chou, Hsiao-Hsuan Hsu and Chun-Hu Cheng

Materials 2023, 16(9), 3306; https://doi.org/10.3390/ma16093306 - 23 Apr 2023

Viewed by 1633

Abstract

In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked [...] Read more.

In this work, we investigate the ferroelectricity of stacked zirconium oxide and hafnium oxide (stacked HfZrO) with different thickness ratios under metal gate stress and simultaneously evaluate the electrical reliability of stacked ferroelectric films. Based on experimental results, we find that the stacked HfZrO films not only exhibited excellent ferroelectricity but also demonstrated a high performance on reliability. The optimized condition of the 45% Zr proportion exhibited a robust ferroelectric polarization value of 32.57 μC/cm², and a polarization current with a peak value of 159.98 μA. Besides this, the ferroelectric stacked HfZrO also demonstrated good reliability with a ten-year lifetime under >−2 V constant voltage stress. Therefore, the appropriate modulation of zirconium proportion in stacked HfZrO showed great promise for integrating in high-performance ferroelectric memory. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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13 pages, 3468 KiB

Open AccessArticle

Rheological Characteristics of Fe–C–Cr(Ni) Alloys

by Silvie Rosypalová, Lenka Řeháčková, Vlastimil Novák, Monika Kawuloková, Petra Váňová, Kateřina Konečná and Barbora Ďuricová

Materials 2023, 16(7), 2656; https://doi.org/10.3390/ma16072656 - 27 Mar 2023

Viewed by 1079

Abstract

The principal objective of this project was to investigate the rheological properties of Fe–C–Cr and Fe–C–Ni-based low-alloy steels using an Anton Paar high-temperature rotational viscometer up to 1550 °C. The emphasis was placed on determining the liquidus temperatures and evaluating the flow and [...] Read more.

The principal objective of this project was to investigate the rheological properties of Fe–C–Cr and Fe–C–Ni-based low-alloy steels using an Anton Paar high-temperature rotational viscometer up to 1550 °C. The emphasis was placed on determining the liquidus temperatures and evaluating the flow and viscosity curves and the temperature dependence of dynamic viscosity. All were studied depending on the change in the content of chromium (0.010–4.863 wt%), nickel (0.001–4.495 wt%), and carbon (0.043–1.563 wt%). It was shown that the dynamic viscosity decreases with increasing nickel content and increases with increasing carbon and chromium content. The experimental data of the flow curves were fitted using the Herschel–Bulkley model with a good agreement between the measured and calculated values. Characterization of the internal structure was performed by SEM and EDX analyses, confirming non-significant changes in the microstructure of the original and remelted samples. The phase composition of the selected samples was also determined using JMatPro 12.0 simulation software (Sente Software Ltd., Guildford, UK). Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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10 pages, 1934 KiB

Open AccessArticle

Structural, Magnetic and Vibrational Properties of Van Der Waals Ferromagnet CrBr₃ at High Pressure

by Olga Lis, Denis Kozlenko, Sergey Kichanov, Evgenii Lukin, Ivan Zel and Boris Savenko

Materials 2023, 16(1), 454; https://doi.org/10.3390/ma16010454 - 03 Jan 2023

Cited by 4 | Viewed by 1787

Abstract

The crystal and magnetic structures of van der Waals layered ferromagnet Cr

{Br}_{3}

were studied using X-ray powder diffraction and neutron powder diffraction at pressures up to 23 GPa at ambient temperature and up to 2.8 GPa in the temperature range 6–300 [...] Read more.

The crystal and magnetic structures of van der Waals layered ferromagnet Cr

{Br}_{3}

were studied using X-ray powder diffraction and neutron powder diffraction at pressures up to 23 GPa at ambient temperature and up to 2.8 GPa in the temperature range 6–300 K, respectively. The vibration spectra of Cr

{Br}_{3}

were studied using Raman spectroscopy at pressures up to 23 GPa at ambient temperature. The anomalous pressure behavior of structural parameters and vibrational modes was observed, associated with a gradual isostructural phase transition in the pressure range 2.5–7 GPa. The Curie temperature T_C reduced rapidly with a pressure coefficient

d T_{C} / d P = - 4.1 (4)

K/GPa. A full suppression of the ferromagnetic state was expected at P_C~8.4 GPa, where onset of the antiferromagnetic spin arrangement or magnetically disordered state may take place. Anomalies in Raman spectra at P~15 GPa point to another possible phase transformation in Cr

{Br}_{3}

, which may be related to the proximity of metallization of this van der Waals ferromagnet. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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13 pages, 4379 KiB

Open AccessArticle

Study of the Functionalities of a Biochar Electrode Combined with a Photoelectrochemical Cell

by Spyridon Giannakopoulos, John Vakros, Ioannis D. Manariotis, Dionissios Mantzavinos and Panagiotis Lianos

Materials 2023, 16(1), 43; https://doi.org/10.3390/ma16010043 - 21 Dec 2022

Cited by 2 | Viewed by 1160

Abstract

Biochar has been obtained by pyrolysis of spent malt rootlets under limited oxygen supply and further activated by mixing with KOH and pyrolyzed again at high temperature. The total specific surface area of such activated biochar was 1148 m² g⁻¹, [...] Read more.

Biochar has been obtained by pyrolysis of spent malt rootlets under limited oxygen supply and further activated by mixing with KOH and pyrolyzed again at high temperature. The total specific surface area of such activated biochar was 1148 m² g⁻¹, while that of micropores was 690 m² g⁻¹. This biochar was used to make a functional electrode by deposition on carbon cloth and was combined with a photoelectrochemical cell. The biochar electrode functioned as a supercapacitor in combination with the electrolyte of the cell, reaching a specific capacity of 98 Fg⁻¹, and it was capable of storing charges generated by the cell, proving current flow both under illumination and in the dark. The same electrode could be used as an air-cathode providing oxygen reduction functionality and thus demonstrating interesting electrocatalyst properties. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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9 pages, 1620 KiB

Open AccessEditor’s ChoiceArticle

On the Quantum Confinement Effects in Ultrathin PdO Films by Experiment and Theory

by Alexandros Barnasas, Christos S. Garoufalis, Dimitrios I. Anyfantis, Panagiotis Poulopoulos and Sotirios Baskoutas

Materials 2022, 15(23), 8700; https://doi.org/10.3390/ma15238700 - 06 Dec 2022

Cited by 1 | Viewed by 1387

Abstract

Radio frequency magnetron sputtering conducted in a high vacuum with a base pressure of

1 \times 10^{- 6}

mbar was used to deposit ultrathin palladium films on Corning glass. The thickness of these films ranged from 0.4 to 13 nanometers. PdO films [...] Read more.

Radio frequency magnetron sputtering conducted in a high vacuum with a base pressure of

1 \times 10^{- 6}

mbar was used to deposit ultrathin palladium films on Corning glass. The thickness of these films ranged from 0.4 to 13 nanometers. PdO films were produced after being post-annealed in a furnace at temperatures of 530 degrees Celsius in the presence of air. The results of an atomic force microscopy study showed that the material possessed a high crystalline quality with a low roughness. When looking at Tauc plots to determine the position of the direct optical band gap, the thicker films show a value that is relatively close to 2.2 eV. When the film thickness was reduced all the way down to 0.7 nm, a significant “blue shift” of more than 0.5 eV was observed. In order to provide a more in-depth understanding of the experiment, theoretical calculations based on the Hartree–Fock approximation as applied to an electron-hole system were performed in the framework of the effective mass approximation. The findings are regarded as empirical proof of the existence of quantum confinement effects. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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13 pages, 301 KiB

Open AccessArticle

A Phase-Field Approach to Continuum Damage Mechanics

by Angelo Morro

Materials 2022, 15(21), 7671; https://doi.org/10.3390/ma15217671 - 31 Oct 2022

Cited by 2 | Viewed by 1101

Abstract

This paper develops a phase-field approach to describe the damage within continuum mechanics. The body is associated with the standard stresses and body forces of macroscopic character. As is the case in many contexts, the phase field is a scalar variable whose time [...] Read more.

This paper develops a phase-field approach to describe the damage within continuum mechanics. The body is associated with the standard stresses and body forces of macroscopic character. As is the case in many contexts, the phase field is a scalar variable whose time rate is governed by a constitutive equation. The generality of the approach allows the modeling of non-stationary heat conduction, mechanical hysteretic effects, and the macroscopic damage. The thermodynamic consistency is investigated through the constraint of the Clausius–Duhem inequality following the standard procedure of Rational Thermodynamics. The entropy production is considered as a constitutive function; this view was proved to be essential in the elaboration of hysteretic models. Here, the scheme is improved by viewing the entropy production as a sum of two terms, one induced by the other constitutive equations and one given by a constitutive equation of the entropy production per se. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

20 pages, 8306 KiB

Open AccessArticle

A Novel Interstitial Site in Binary Rock-Salt Compounds

by Neeraj Mishra and Guy Makov

Materials 2022, 15(17), 6015; https://doi.org/10.3390/ma15176015 - 31 Aug 2022

Cited by 4 | Viewed by 1634

Abstract

The energetic and mechanical stability of interstitial point defects in binary rock-salt materials were studied using the first-principles method. A novel, stable, and energetically competitive interstitial site (base-interstitial) was identified for anion interstitials in rock-salts. The formation energies of base-interstitial defects were compared [...] Read more.

The energetic and mechanical stability of interstitial point defects in binary rock-salt materials were studied using the first-principles method. A novel, stable, and energetically competitive interstitial site (base-interstitial) was identified for anion interstitials in rock-salts. The formation energies of base-interstitial defects were compared with well-explored tetrahedral (body-interstitial) and split interstitials and were found to be energetically highly competitive. For alkali halides and silver bromide, the lowest formation energies are associated with the base-interstitial site and the <110> split interstitial, which are therefore the predominant interstitial sites. However, split interstitials were found to be the energetically preferred configuration in metal monochalcogenide systems. Electronic band structures are affected by the presence of interstitial defects in rock-salt structures. In particular, the Fermi level is shifted below the valence band maxima for the body, base, and split interstitials in metal halides, indicating p-type conductivity. However, the Fermi level remains within the bandgap for metal monochalcogenides, indicating no preferred conductivity for base- and split-interstitial defects. Allowing the defects to be charged changes the relative stability of the interstitial sites. However, the new base-interstitial site remains preferred over a range of potentials for alkali halides. The anion base-interstitial is found to form a triatomic entity with the nearest lattice anions that affect the electronic structure relative to the body interstitial. The discovery of a new interstitial site affects our understanding of defects in binary rock-salts, including structure and dynamics as well as associated thermodynamic and kinetic properties that are interstitial dependent. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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18 pages, 4711 KiB

Open AccessArticle

Denouement of the Energy-Amplitude and Size-Amplitude Enigma for Acoustic-Emission Investigations of Materials

by Sarah M. Kamel, Nora M. Samy, László Z. Tóth, Lajos Daróczi and Dezső L. Beke

Materials 2022, 15(13), 4556; https://doi.org/10.3390/ma15134556 - 28 Jun 2022

Cited by 5 | Viewed by 1278

Abstract

There are many systems producing crackling noise (avalanches) in materials. Temporal shapes of avalanches, U(t) (U is the detected voltage signal, t is the time), have self-similar behaviour and the normalized U(t) function (e.g., dividing both [...] Read more.

There are many systems producing crackling noise (avalanches) in materials. Temporal shapes of avalanches, U(t) (U is the detected voltage signal, t is the time), have self-similar behaviour and the normalized U(t) function (e.g., dividing both the values of U and t by S^1/2, where S is the avalanche area), averaged for fixed S, should be the same, independently of the type of materials or avalanche mechanisms. However, there are experimental evidences that the temporal shapes of avalanches do not scale completely in a universal way. The self-similarity also leads to universal power-law-scaling relations, e.g., between the energy, E, and the peak amplitude, A_m, or between S and A_m. There are well-known enigmas, where the above exponents in acoustic emission measurements are rather close to 2 and 1, respectively, instead of

E ~ A_{m}^{3}

and

S ~ A_{m}^{2}

, obtained from the mean field theory, MFT. We show, using a theoretically predicted averaged function for the fixed avalanche area,

U (t) = a t \exp (- b t^{2})

(where a and b are non-universal, material-dependent constants), that the scaling exponents can be different from the MFT values. Normalizing U by A_m and t by t_m (the time belonging to the A_m: rise time), we obtain

t_{m} ~ A_{m}^{1 - φ}

(the MFT values can be obtained only if φ would be zero). Here, φ is expected to be material-independent and to be the same for the same mechanism. Using experimental results on martensitic transformations in two different shape-memory single-crystals, φ = 0.8 ± 0.1 was obtained (φ is the same for both alloys). Thus, dividing U by A_m as well as t by

A_{m}^{1 - φ}

(~t_m) leads to the same common, normalized temporal shape for different, fixed values of S. This normalization can also be used in general for other experimental results (not only for acoustic emission), which provide information about jerky noises in materials. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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14 pages, 4023 KiB

Open AccessArticle

Effect of Doping on the Electronic Structure of the Earth’s Lower Mantle Compounds: FeXO₃ with X = C, Al, Si

by Evgeniy D. Chernov, Alexey A. Dyachenko and Alexey V. Lukoyanov

Materials 2022, 15(3), 1080; https://doi.org/10.3390/ma15031080 - 29 Jan 2022

Cited by 1 | Viewed by 2119

Abstract

The effect of the mutual doping of C, Si, and Al atoms on the electronic structure and magnetic properties of FeXO₃ (X = C, Al, Si) compounds, which are constituent compounds of the Earth’s lower mantle, was studied. In our first principles [...] Read more.

The effect of the mutual doping of C, Si, and Al atoms on the electronic structure and magnetic properties of FeXO₃ (X = C, Al, Si) compounds, which are constituent compounds of the Earth’s lower mantle, was studied. In our first principles calculations, it was found that doping with carbon for both FeSiO₃ and FeAlO₃ leads to the transition of the compound from a half-metallic state to a metallic one. The values of the magnetic moments of Fe were obtained for pure and doped compounds. For the doped compounds, there is a tendency of the Fe magnetic moment to increase with the growth in the number of substituted ions in the case of replacing Si with C and Si for Al; on the contrary, in the case of replacing Al with C and Si, a decrease in the magnetic moment was revealed. For FeXO₃ (X = C, Al, Si), the obtained magnetic moment values were found to be in a good agreement with the known experimental data. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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12 pages, 1810 KiB

Open AccessArticle

The Selective Transport of Ions in Charged Nanopore with Combined Multi-Physics Fields

by Pengfei Ma, Jianxiang Zheng, Danting Zhao, Wenjie Zhang, Gonghao Lu, Lingxin Lin, Zeyuan Zhao, Zijing Huang and Liuxuan Cao

Materials 2021, 14(22), 7012; https://doi.org/10.3390/ma14227012 - 19 Nov 2021

Cited by 9 | Viewed by 2214

Abstract

The selective transport of ions in nanopores attracts broad interest due to their potential applications in chemical separation, ion filtration, seawater desalination, and energy conversion. The ion selectivity based on the ion dehydration and steric hindrance is still limited by the very similar [...] Read more.

The selective transport of ions in nanopores attracts broad interest due to their potential applications in chemical separation, ion filtration, seawater desalination, and energy conversion. The ion selectivity based on the ion dehydration and steric hindrance is still limited by the very similar diameter between different hydrated ions. The selectivity can only separate specific ion species, lacking a general separation effect. Herein, we report the highly ionic selective transport in charged nanopore through the combination of hydraulic pressure and electric field. Based on the coupled Poisson–Nernst–Planck (PNP) and Navier–Stokes (NS) equations, the calculation results suggest that the coupling of hydraulic pressure and electric field can significantly enhance the ion selectivity compared to the results under the single driven force of hydraulic pressure or electric field. Different from the material-property-based ion selective transport, this method endows the general separation effect between different kinds of ions. Through the appropriate combination of hydraulic pressure and electric field, an extremely high selectivity ratio can be achieved. Further in-depth analysis reveals the influence of nanopore diameter, surface charge density and ionic strength on the selectivity ratio. These findings provide a potential route for high-performance ionic selective transport and separation in nanofluidic systems. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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30 pages, 12223 KiB

Open AccessArticle

Binary Dye Removal from Simulated Wastewater Using Reduced Graphene Oxide Loaded with Fe-Cu Bimetallic Nanocomposites Combined with an Artificial Neural Network

by Ling Xin, Xianliang Wu, Yiqiu Xiang, Shengsheng Zhang, Xianfei Huang and Huijuan Liu

Materials 2021, 14(18), 5268; https://doi.org/10.3390/ma14185268 - 13 Sep 2021

Cited by 3 | Viewed by 1851

Abstract

Reduced graphene oxide loaded with an iron-copper nanocomposite was prepared in this study, using graphene oxide as a carrier and ferrous sulfate, copper chloride and sodium borohydride as raw materials. The obtained material was prepared for eliminating hazardous dye carmine and the binary [...] Read more.

Reduced graphene oxide loaded with an iron-copper nanocomposite was prepared in this study, using graphene oxide as a carrier and ferrous sulfate, copper chloride and sodium borohydride as raw materials. The obtained material was prepared for eliminating hazardous dye carmine and the binary dye mixture of carmine and Congo red. The process of carmine dye removal by the nanocomposite was modeled and optimized through response surface methodology and artificial intelligence (artificial neural network–particle swarm optimization and artificial neural network–genetic algorithm) based on single-factor experiments. The results demonstrated that the surface area of the nanocomposite was 41.255 m²/g, the pore size distribution was centered at 2.125 nm, and the saturation magnetization was up to 108.33 emu/g. A comparison of the material before and after the reaction showed that the material could theoretically be reused three times. The absolute error between the predicted and experimental values derived by using artificial neural network–particle swarm optimization was the smallest, indicating that this model was suitable to remove carmine from simulated wastewater. The dose factor was the key factor in the adsorption process. This process could be described with the pseudo-second-order kinetic model, and the maximum adsorption capacity was 1848.96 mg/g. The removal rate of the mixed dyes reached 96.85% under the optimal conditions (the dosage of rGO/Fe/Cu was 20 mg, the pH was equal to 4, the initial concentration of the mixed dyes was 500 mg/L, and the reaction time was 14 min), reflecting the excellent adsorption capability of the material. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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12 pages, 1691 KiB

Open AccessEditor’s ChoiceArticle

Magneto-Optical Transport Properties of Type-II Nodal Line Semimetals

by Yanmei Sun, Jing Li, Hui Zhao, Meimei Wu and Hui Pan

Materials 2021, 14(11), 3035; https://doi.org/10.3390/ma14113035 - 02 Jun 2021

Cited by 3 | Viewed by 2112

Abstract

We investigate the magneto-optical transport properties and Landau levels of type-II nodal line semimetals. The tilted liner dispersion in type-II nodal line semimetals makes the conduction band and valence band asymmetric, and Landau levels are coupling in the presence of a magnetic field. [...] Read more.

We investigate the magneto-optical transport properties and Landau levels of type-II nodal line semimetals. The tilted liner dispersion in type-II nodal line semimetals makes the conduction band and valence band asymmetric, and Landau levels are coupling in the presence of a magnetic field. We find the background of absorption peaks is curved. The oscillation peaks are tailless with the change of magnetic field. Through tuning tilt term, we find the absorption peaks of optical conductivity change from incomplete degenerate structure to splitting double peaks structure. We also find interband absorption peaks is no longer zero in the imaginary part of Hall conductivity. With the change of the tilt term, the contribution of the absorption peak has two forms, one is that the negative peak only appears at high frequencies, and the other is two adjacent peaks with opposite signs. In addition, the resistivity, circularly polarized light and magnetic oscillation of Hall conductivity are studied. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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19 pages, 4716 KiB

Open AccessArticle

Detailed Inspection of γ-ray, Fast and Thermal Neutrons Shielding Competence of Calcium Oxide or Strontium Oxide Comprising Bismuth Borate Glasses

by Gandham Lakshminarayana, Youssef Elmahroug, Ashok Kumar, Huseyin Ozan Tekin, Najeh Rekik, Mengge Dong, Dong-Eun Lee, Jonghun Yoon and Taejoon Park

Materials 2021, 14(9), 2265; https://doi.org/10.3390/ma14092265 - 27 Apr 2021

Cited by 32 | Viewed by 2375

Abstract

For both the B₂O₃-Bi₂O₃-CaO and B₂O₃-Bi₂O₃-SrO glass systems, γ-ray and neutron attenuation qualities were evaluated. Utilizing the Phy-X/PSD program, within the 0.015–15 MeV energy range, linear [...] Read more.

For both the B₂O₃-Bi₂O₃-CaO and B₂O₃-Bi₂O₃-SrO glass systems, γ-ray and neutron attenuation qualities were evaluated. Utilizing the Phy-X/PSD program, within the 0.015–15 MeV energy range, linear attenuation coefficients (µ) and mass attenuation coefficients (μ/ρ) were calculated, and the attained μ/ρ quantities match well with respective simulation results computed by MCNPX, Geant4, and Penelope codes. Instead of B₂O₃/CaO or B₂O₃/SrO, the Bi₂O₃ addition causes improved γ-ray shielding competence, i.e., rise in effective atomic number (Z_eff) and a fall in half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP). Exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) were derived using a geometric progression (G–P) fitting approach at 1–40 mfp penetration depths (PDs), within the 0.015–15 MeV range. Computed radiation protection efficiency (RPE) values confirm their excellent capacity for lower energy photons shielding. Comparably greater density (7.59 g/cm³), larger μ, μ/ρ, Z_eff, equivalent atomic number (Z_eq), and RPE, with the lowest HVL, TVL, MFP, EBFs, and EABFs derived for 30B₂O₃-60Bi₂O₃-10SrO (mol%) glass suggest it as an excellent γ-ray attenuator. Additionally, 30B₂O₃-60Bi₂O₃-10SrO (mol%) glass holds a commensurably bigger macroscopic removal cross-section for fast neutrons (Σ_R) (=0.1199 cm⁻¹), obtained by applying Phy-X/PSD for fast neutrons shielding, owing to the presence of larger wt% of ‘Bi’ (80.6813 wt%) and moderate ‘B’ (2.0869 wt%) elements in it. 70B₂O₃-5Bi₂O₃-25CaO (mol%) sample (B: 17.5887 wt%, Bi: 24.2855 wt%, Ca: 11.6436 wt%, and O: 46.4821 wt%) shows high potentiality for thermal or slow neutrons and intermediate energy neutrons capture or absorption due to comprised high wt% of ‘B’ element in it. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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14 pages, 7277 KiB

Open AccessEditor’s ChoiceArticle

Omega Phase Formation in Ti–3wt.%Nb Alloy Induced by High-Pressure Torsion

by Anna Korneva, Boris Straumal, Askar Kilmametov, Alena Gornakova, Anna Wierzbicka-Miernik, Lidia Lityńska-Dobrzyńska, Robert Chulist, Łukasz Gondek, Grzegorz Cios and Paweł Zięba

Materials 2021, 14(9), 2262; https://doi.org/10.3390/ma14092262 - 27 Apr 2021

Cited by 7 | Viewed by 2145

Abstract

It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys [...] Read more.

It is well known that severe plastic deformation not only leads to strong grain refinement and material strengthening but also can drive phase transformations. A study of the fundamentals of α → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Before HPT, a Ti–3wt.%Nb alloy was annealed at two different temperatures in order to obtain the α-phase state with different amounts of niobium. X-ray diffraction analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the characterisation of phase transitions and evolution of the microstructure. A small amount of the β-phase was found in the initial states, which completely transformed into the ω-phase during the HPT process. During HPT, strong grain refinement in the α-phase took place, as did partial transformation of the α- into the ω-phase. Therefore, two kinds of ω-phase, each with different chemical composition, were obtained after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the α-phase. It was also found that the transformation of the α-phase into the ω-phase depended on the Nb concentration in the α-Ti phase. The less Nb there was in the α-phase, the more of the α-phase was transformed into the ω-phase. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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12 pages, 6841 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Selective Extraction of Nonfullerene Acceptors from Bulk-Heterojunction Layer in Organic Solar Cells for Detailed Analysis of Microstructure

by Masahiro Nakano, Akira Takahara, Kenji Genda, Md. Shahiduzzaman, Makoto Karakawa, Tetsuya Taima and Kohshin Takahashi

Materials 2021, 14(9), 2107; https://doi.org/10.3390/ma14092107 - 21 Apr 2021

Cited by 3 | Viewed by 2210

Abstract

Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor [...] Read more.

Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor materials. In our previous study on the microstructure of a BHJ film composed of donor polymers and fullerene-based acceptors, we analyzed donor polymer-only films after selectively extracting fullerene-based acceptors from the film by atomic force microscopy (AFM). Not only was AFM suitable for a clear analysis of the morphology of the donor polymers in the BHJ film, but it also allowed us to approximate the acceptor morphology by analyzing the pores in the extracted films. Herein we report a method for the selective extraction of nonfullerene acceptors (NFAs) from a BHJ layer in OSCs and provide a detailed analysis of the remaining BHJ films based upon AFM. We found that butyl glycidyl ether is an effective solvent to extract NFAs from BHJ films without damaging the donor polymer films. By using the selective extraction method, the morphologies of NFA-free BHJ films fabricated under various conditions were studied in detail. The results may be useful for the optimization of BHJ film structures composed of NFAs and donor polymers. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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12 pages, 11588 KiB

Open AccessEditor’s ChoiceArticle

Preparation and Thermal Conductivity of Epoxy Resin/Graphene-Fe₃O₄ Composites

by Zhong Wu, Jingyun Chen, Qifeng Li, Da-Hai Xia, Yida Deng, Yiwen Zhang and Zhenbo Qin

Materials 2021, 14(8), 2013; https://doi.org/10.3390/ma14082013 - 16 Apr 2021

Cited by 7 | Viewed by 2387

Abstract

By modifying the bonding of graphene (GR) and Fe₃O₄, a stable structure of GR-Fe₃O₄, namely magnetic GR, was obtained. Under the induction of a magnetic field, it can be orientated in an epoxy resin (EP) [...] Read more.

By modifying the bonding of graphene (GR) and Fe₃O₄, a stable structure of GR-Fe₃O₄, namely magnetic GR, was obtained. Under the induction of a magnetic field, it can be orientated in an epoxy resin (EP) matrix, thus preparing EP/GR-Fe₃O₄ composites. The effects of the content of GR and the degree of orientation on the thermal conductivity of the composites were investigated, and the most suitable Fe₃O₄ load on GR was obtained. When the mass ratio of GR and Fe₃O₄ was 2:1, the thermal conductivity could be increased by 54.8% compared with that of pure EP. Meanwhile, EP/GR-Fe₃O₄ composites had a better thermal stability, dynamic thermomechanical properties, and excellent electrical insulation properties, which can meet the requirements of electronic packaging materials. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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9 pages, 5417 KiB

Open AccessArticle

Discontinuous Dissolution Reaction in a Fe-13.5 at. % Zn Alloy

by Paweł Zięba, Mateusz Chronowski, Jarosław Opara, Olga A. Kogtenkova and Boris B. Straumal

Materials 2021, 14(8), 1939; https://doi.org/10.3390/ma14081939 - 13 Apr 2021

Cited by 2 | Viewed by 1354

Abstract

The dissolution process of a lamellar structure with α and Γ phases formed during a discontinuous precipitation reaction is investigated here with a Fe-13.5 at. % Zn alloy by means of optical microscopy and scanning and transmission electron microscopy. The α phase is [...] Read more.

The dissolution process of a lamellar structure with α and Γ phases formed during a discontinuous precipitation reaction is investigated here with a Fe-13.5 at. % Zn alloy by means of optical microscopy and scanning and transmission electron microscopy. The α phase is a solute-depleted solid solution and the Γ phase is the intermetallic compound Fe₃Zn₁₀. The examination reveals that the dissolution occurs in a discontinuous mode by a receding of the former reaction front of the discontinuous precipitation towards the position of the original grain boundary. A new solid solution in the post-dissolution area is especially inhomogeneous and reflects the former locations of the Γ lamellae (“ghost images”) and the receding reaction front (“ghost lines”). A simulation procedure is applied to determine the Zn concentration profiles left in the post-dissolution region. Their shapes are mostly affected by the Zn content at the positions where the Γ lamellae have just been dissolved, which was also confirmed by the quantitative microchemical analysis. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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9 pages, 3146 KiB

Open AccessEditor’s ChoiceArticle

Role of Anharmonic Interactions for Vibration Density of States in α-Cristobalite

by Yongda Huang, Jian Zhou, Guanjie Wang and Zhimei Sun

Materials 2021, 14(3), 617; https://doi.org/10.3390/ma14030617 - 29 Jan 2021

Cited by 2 | Viewed by 2097

Abstract

The vibrational density of states (VDOS) of solids in the low-energy regime controls the thermal and transport properties of materials, such as heat capacity, heat conduction, free energy and entropy. In α-Cristobalite, the low-frequency part of vibration density of states (VDOS) has many [...] Read more.

The vibrational density of states (VDOS) of solids in the low-energy regime controls the thermal and transport properties of materials, such as heat capacity, heat conduction, free energy and entropy. In α-Cristobalite, the low-frequency part of vibration density of states (VDOS) has many common features with the Boson peak in silica glass of matched densities. Recent theoretical work reported that anharmonic phonon–phonon interactions were critical for the low-frequency part of VDOS in α-Cristobalite. Therefore, it is urgent to identify the role of different anharmonic interactions from first principles. In this paper, we focus on the main peak of the low-frequency part of VDOS in α-Cristobalite. Calculated by our own developed codes and first principles, we find that the quartic anharmonic interaction can increase the frequency of the peak, while the cubic anharmonic can reduce the frequency and change the shape of the peak. Meanwhile, the anharmonic interactions are critical for the temperature effect. Therefore, we calculated the temperature-dependent property of the peak. We find that the frequency of the peak is directly proportional to the temperature. The atomic displacement patterns of different temperatures also confirm the above conclusion. All our calculations converged well. Moreover, our basic results agree well with other published results. Finally, we highlight that our codes offer a general and reliable way to calculate the VDOS with temperature. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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8 pages, 2376 KiB

Open AccessArticle

The Texture and Structure of the Melt-Spun Co₂MnAl-Type Heusler Alloy

by Pavel Diko, Viktor Kavečanský, Tomáš Ryba, Lucia Frolová, Rastislav Varga and Zuzana Vargová

Materials 2021, 14(3), 501; https://doi.org/10.3390/ma14030501 - 21 Jan 2021

Cited by 2 | Viewed by 1667

Abstract

The structure of the Co₂MnAl_-type Heusler alloy in the form of a melt-spun ribbon was studied by electron microscopy, electron back-scattered diffraction (EBSD), and X-ray diffraction. The melt-spun ribbon consists of a homogeneous single-phase disordered Heusler alloy at the [...] Read more.

The structure of the Co₂MnAl_-type Heusler alloy in the form of a melt-spun ribbon was studied by electron microscopy, electron back-scattered diffraction (EBSD), and X-ray diffraction. The melt-spun ribbon consists of a homogeneous single-phase disordered Heusler alloy at the wheel side of the ribbon and an inhomogeneous single-phase alloy, formed by cellular or dendritic growth, at the free surface of the ribbon. Cellular growth causes the formation of an inhomogeneous distribution of the elemental constituents, with a higher Co and Al concentration in the centre of the cells or dendritic arms and a higher concentration of Mn at the cell boundaries. The EBSD analysis shows that the columnar crystals grow in the <111> crystal direction and are declined by about 10° against the direction of the spinning. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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14 pages, 5623 KiB

Open AccessArticle

Heterostructured CoO_x–TiO₂ Mesoporous/Photonic Crystal Bilayer Films for Enhanced Visible-Light Harvesting and Photocatalysis

by Stelios Loukopoulos, Alexia Toumazatou, Elias Sakellis, Evangelia Xenogiannopoulou, Nikos Boukos, Athanasios Dimoulas and Vlassis Likodimos

Materials 2020, 13(19), 4305; https://doi.org/10.3390/ma13194305 - 26 Sep 2020

Cited by 6 | Viewed by 2417

Abstract

Heterostructured bilayer films, consisting of co-assembled TiO₂ photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoO_x nanoclusters, are demonstrated as highly efficient visible-light photocatalysts. Broadband visible-light activation of the bilayer [...] Read more.

Heterostructured bilayer films, consisting of co-assembled TiO₂ photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoO_x nanoclusters, are demonstrated as highly efficient visible-light photocatalysts. Broadband visible-light activation of the bilayer films was implemented by the surface modification of both titania layers with nanoscale clusters of Co oxides relying on the chemisorption of Co acetylacetonate complexes on TiO₂, followed by post-calcination. Tuning the slow photon regions of the inverse opal supporting layer to the visible-light absorption of surface CoO_x oxides resulted in significant amplification of salicylic-acid photodegradation under visible and ultraviolet (UV)–visible light (Vis), outperforming benchmark P25 films of higher titania loading. This enhancement was related to the spatially separated contributions of slow photon propagation in the inverse opal support layer assisted by Bragg reflection toward the CoO_x-modified mesoporous P25 top layer. This effect indicates that photonic crystals may be highly effective as both photocatalytically active and backscattering layers in multilayer photocatalytic films. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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23 pages, 6996 KiB

Open AccessEditor’s ChoiceReview

RE-Based Inorganic-Crystal Nanofibers Produced by Electrospinning for Photonic Applications

by Alessandra Toncelli

Materials 2021, 14(10), 2679; https://doi.org/10.3390/ma14102679 - 20 May 2021

Cited by 6 | Viewed by 2322

Abstract

Electrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and [...] Read more.

Electrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and versatility, which has permitted to obtain a large variety of multifunctional compositions with a rich collection of new possible applications. Rare-earth doped materials possess many remarkable features that have been exploited, for example, for diode pumped bulk solid-state lasers in the visible and near infrared regions, or for biomedical applications when grown in nanometric form. In the last few decades, electrospinning preparation of rare-earth-doped crystal nanofibers has been developed and many different materials have been successfully grown. Crystal host, crystal quality and nanosized shape can deeply influence the optical properties of embedded rare earth ions; therefore, a large number of papers has recently been devoted to the growth and characterization of rare earth doped nanofibers with the electrospinning technique and an up-to-date review of this rapidly developing topic is missing; This review paper is devoted to the presentation of the main results obtained in this field up to now with particular insight into the optical characterization of the various materials grown with this technique. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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21 pages, 26047 KiB

Open AccessReview

Carbon-Based Nanocomposites as Fenton-Like Catalysts in Wastewater Treatment Applications: A Review

by Ling Xin, Jiwei Hu, Yiqiu Xiang, Caifang Li, Liya Fu, Qiuhua Li and Xionghui Wei

Materials 2021, 14(10), 2643; https://doi.org/10.3390/ma14102643 - 18 May 2021

Cited by 23 | Viewed by 4248

Abstract

Advanced oxidation (e.g., fenton-like reagent oxidation and ozone oxidation) is a highly important technology that uses strong oxidizing free radicals to degrade organic pollutants and mineralize them. The fenton-like reactions have the characteristics of low cost, simple operation, thorough reaction and no secondary [...] Read more.

Advanced oxidation (e.g., fenton-like reagent oxidation and ozone oxidation) is a highly important technology that uses strong oxidizing free radicals to degrade organic pollutants and mineralize them. The fenton-like reactions have the characteristics of low cost, simple operation, thorough reaction and no secondary pollution. Fenton-like reagents refer to a strong oxidation system composed of transition metal ions (e.g., Fe³⁺, Mn²⁺ and Ag⁺) and oxidants (hydrogen peroxide, potassium persulfate, sodium persulfate, etc). Graphene and carbon nanotube possess a distinctive mechanical strength, flexibility, electrical and thermal conductivity and a very large specific surface area, which can work as an excellent carrier to disperse the catalyst and prevent its agglomeration. Fullerene can synergize with iron-based materials to promote the reaction of hydroxyl groups with organic pollutants and enhance the catalytic effect. Fenton-like catalysts influence the catalytic behavior by inducing electron transfer under strong interactions with the support. Due to the short lifespan of free radicals, the treatment effect is usually enhanced with the assistance of external conditions (ultraviolet and electric fields) to expand the application of fenton-like catalysts in water treatment. There are mainly light-fenton, electro-fenton and photoelectric-fenton methods. Fenton-like catalysts can be prepared by hydrothermal method, impregnation and coordination-precipitation approaches. The structures and properties of the catalysts are characterized by a variety of techniques, such as high-resolution transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure spectroscopy. In this paper, we review the mechanisms, preparation methods, characterizations and applications status of fenton-like reagents in industrial wastewater treatment, and summarize the recycling of these catalysts and describe prospects for their future research directions. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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