Research

11 pages, 4329 KiB

Open AccessArticle

Effects of Sintering Processes on Microstructure Evolution, Crystallite, and Grain Growth of MoO₂ Powder

by Jongbeom Lee, Jinyoung Jeong, Hyowon Lee, Jaesoung Park, Jinman Jang and Haguk Jeong

Crystals 2023, 13(9), 1311; https://doi.org/10.3390/cryst13091311 - 28 Aug 2023

Viewed by 933

MoO₂ micro-powders with a mean pore size of 3.4 nm and specific surface area of 2.5 g/cm³ were compacted by dry pressing, then pressureless sintered at a temperature of 1000–1150 °C for 2 h or for a sintering time of 0.5–12 [...] Read more.

MoO₂ micro-powders with a mean pore size of 3.4 nm and specific surface area of 2.5 g/cm³ were compacted by dry pressing, then pressureless sintered at a temperature of 1000–1150 °C for 2 h or for a sintering time of 0.5–12 h at 1050 °C in an N₂ atmosphere. Then, their microstructure evolution for morphology, crystallite, and grain growth were investigated. By sintering at a certain temperature and times, the irregular shape of the MoO₂ powders transformed into an equiaxed structure, owing to the surface energy, which contributed to faster grain growth at the initial stage of sintering. The crystallite and grain sizes exponentially increased with the sintering time, and the growth exponent, n, was approximately 2.8 and 4, respectively. This indicates that the crystallite growth is governed by dislocation-mediated lattice diffusion, and the grain growth is determined by surface diffusion-controlled pore mobility. The increase in sintering temperature increased both crystallite and grain size, which obeyed the Arrhenius equation, and the activation energies were determined to be 95.65 and 76.95 kJmol⁻¹ for crystallite and grain growths, respectively. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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10 pages, 8115 KiB

Open AccessArticle

Study of Crack-Propagation Mechanism of Al_0.1CoCrFeNi High-Entropy Alloy by Molecular Dynamics Method

by Cuixia Liu and Yu Yao

Crystals 2023, 13(1), 11; https://doi.org/10.3390/cryst13010011 - 22 Dec 2022

Cited by 2 | Viewed by 1434

Abstract

The crack propagation mechanism of Al_0.1CoCrFeNi high-entropy alloy (HEA) was investigated with the molecular dynamics method. The pre-crack propagation and stretching processes of single-crystal Al_0.1CoCrFeNi HEA and Al_0.1CoCrFeNi HEA with grain boundaries were simulated. The effects of [...] Read more.

The crack propagation mechanism of Al_0.1CoCrFeNi high-entropy alloy (HEA) was investigated with the molecular dynamics method. The pre-crack propagation and stretching processes of single-crystal Al_0.1CoCrFeNi HEA and Al_0.1CoCrFeNi HEA with grain boundaries were simulated. The effects of strain rates and different crystal structures on the crack propagation of the alloy therein at room temperature were studied. They both exhibited plastic deformation and ductile fracturing, and the crack tip involved dislocations at 45° and 135° under the tensile stress. The dislocations formed in the intrinsic-stacking fault and stacking fault based on hexagonal closely packed structures spread and then accumulated near the grain boundary. At the position where hexagonal closely packed structures were accumulated, the dent was obviously serious at the 1/3 position of the alloy where the fracturing finally occurred. The yield strength for Al_0.1CoCrFeNi HEA with grain boundaries was lower than that of the single-crystal Al_0.1CoCrFeNi HEA. However, Young’s moduli for Al_0.1CoCrFeNi HEA with grain boundaries were higher than those of the single-crystal Al_0.1CoCrFeNi HEA. The grain boundaries can be used as the emission source of dislocations, and it is easier to form dislocations in the-single crystal Al_0.1CoCrFeNi HEA, but the existence of grain boundaries hinders the slippage of dislocations. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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13 pages, 5036 KiB

Open AccessArticle

Properties of Perovskite-like Lanthanum Strontium Ferrite Ceramics with Variation in Lanthanum Concentration

by Daryn B. Borgekov, Artem L. Kozlovskiy, Rafael I. Shakirzyanov, Ainash T. Zhumazhanova, Maxim V. Zdorovets and Dmitriy I. Shlimas

Crystals 2022, 12(12), 1792; https://doi.org/10.3390/cryst12121792 - 09 Dec 2022

Cited by 1 | Viewed by 1395

Abstract

The purpose of this work is to study the effect of lanthanum (La) concentration on the phase formation, conductivity, and thermophysical properties of perovskite-like strontium ferrite ceramics. At the same time, the key difference from similar studies is the study of the possibility [...] Read more.

The purpose of this work is to study the effect of lanthanum (La) concentration on the phase formation, conductivity, and thermophysical properties of perovskite-like strontium ferrite ceramics. At the same time, the key difference from similar studies is the study of the possibility of obtaining two-phase composite ceramics, the presence of various phases in which will lead to a change in the structural, strength, and conductive properties. To obtain two-phase composite ceramics by mechanochemical solid-phase synthesis, the method of the component molar ratio variation was used, which, when mixed, makes it possible to obtain a different ratio of elements and, as a result, to vary the phase composition of the ceramics. Scanning electron microscopy, X-ray phase analysis, and impedance spectroscopy were used as research methods, the combination of which made it possible to comprehensively study the properties of the synthesized ceramics. Analysis of phase changes depending on lanthanum concentration change can be written as follows: (La_0.3Sr_0.7)₂FeO₄/LaSr₂Fe₃O₈ → (La_0.3Sr_0.7)₂FeO₄/LaSr₂Fe₃O₈/Sr₂Fe₂O₅ → (La_0.3Sr_0.7)₂FeO₄/Sr₂Fe₂O₅. Results of impedance spectroscopy showed that with an increase in lanthanum concentration from 0.10 to 0.25 mol in the synthesized ceramics, the value of the dielectric permittivity increases significantly from 40.72 to 231.69, the dielectric loss tangent increases from 1.07 to 1.29 at a frequency of 10,000 Hz, and electrical resistivity decreases from 1.29 × 10⁸ to 2.37 × 10⁷ Ω∙cm. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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8 pages, 4023 KiB

Open AccessArticle

As-Sintered Manganese-Stabilized Zirconia Ceramics with Excellent Electrical Conductivity

by Ling Gao, Ruidong Guan, Shengnan Zhang, Hao Zhi, Changqing Jin, Lihua Jin, Yongxing Wei and Jianping Wang

Crystals 2022, 12(5), 620; https://doi.org/10.3390/cryst12050620 - 27 Apr 2022

Cited by 3 | Viewed by 1538

Abstract

As promising electrolyte materials in intermediate-temperature solid oxide fuel cells (IT-SOFCs), Sc-stabilized ZrO

_{2}

(ScSZ) and Y-stabilized ZrO

_{2}

(YSZ) electrolytes continue to be plagued by high cost and low intermediate conductivity. To mitigate these problems, Mn has been chosen as a new [...] Read more.

As promising electrolyte materials in intermediate-temperature solid oxide fuel cells (IT-SOFCs), Sc-stabilized ZrO

_{2}

(ScSZ) and Y-stabilized ZrO

_{2}

(YSZ) electrolytes continue to be plagued by high cost and low intermediate conductivity. To mitigate these problems, Mn has been chosen as a new stabilization element for the synthesis of Mn-stabilized ZrO

_{2}

ceramics (MnSZ) through solid state sintering. Microstructures and electrical properties of micron-crystalline

{Zr}_{1 - x} {Mn}_{x}

O

_{2 - δ}

(x = 0.15, 0.20 and 0.25) ceramics electrolytes for IT-SOFCs have been systematically evaluated. Within the applied doping content, Mn

^{2 +}

ions can enter the ZrO

_{2}

crystal lattice, leading to the formation of single cubic phase samples. Electrical conductivity measurements in the temperature range between 400 °C and 1000 °C show a sharp increase in conductivity due to Mn doping. The highest conductivity is obtained from the Zr

_{0.75}

Mn

_{0.25}

O

_{2 - δ}

samples, being 0.0144 S/cm at 600 °C and 0.182 S/cm at 1000 °C. The electrical conductivity at 600 °C is twice higher than that of the YSZ and two orders of magnitude higher than that of the ScSZ. These properties can fulfill the conductivity requirement (∼1

\times 10^{- 2}

S/cm) for the electrolyte. Therefore, based on this study, we propose that Mn stabilized ZrO

_{2}

is a promising candidate as a solid electrolyte for IT-SOFCs. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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23 pages, 998 KiB

Open AccessArticle

Analysis of Electromagnetic Effects on Vibration of Functionally Graded GPLs Reinforced Piezoelectromagnetic Plates on an Elastic Substrate

by Mohammed Sobhy and F. H. H. Al Mukahal

Crystals 2022, 12(4), 487; https://doi.org/10.3390/cryst12040487 - 31 Mar 2022

Cited by 10 | Viewed by 1840

Abstract

A new nanocomposite piezoelectromagnetic plate model is developed for studying free vibration based on a refined shear deformation theory (RDPT). The present model is composed of piezoelectromagnetic material reinforced with functionally graded graphene platelets (FG-GPLs). The nanocomposite panel rests on Winkler–Pasternak foundation and [...] Read more.

A new nanocomposite piezoelectromagnetic plate model is developed for studying free vibration based on a refined shear deformation theory (RDPT). The present model is composed of piezoelectromagnetic material reinforced with functionally graded graphene platelets (FG-GPLs). The nanocomposite panel rests on Winkler–Pasternak foundation and is subjected to external electric and magnetic potentials. It is assumed that the electric and magnetic properties of the GPLs are proportional to those of the electromagnetic materials. The effective material properties of the plate are estimated based on the modified Halpin–Tsai model. A refined graded rule is introduced to govern the variation in the volume fraction of graphene through the thickness of the plate. The basic partial differential equations are provided based on Hamilton’s principle and then solved analytically to obtain the eigenfrequency for different boundary conditions. To check the accuracy of the present formulations, the depicted results are compared with the published ones. Moreover, impacts of the variation in elastic foundation stiffness, plate geometry, electric potential, magnetic potential, boundary conditions and GPLs weight fraction on the vibration of the smart plate are detailed and discussed. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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11 pages, 3835 KiB

Open AccessArticle

Deposition of CdZnTe Films with CSS Method on Different Substrates for Nuclear Radiation Detector Applications

by Bin Yu, Chenggang Xu, Mingxing Xie, Meng Cao, Jijun Zhang, Yucheng Jiang and Linjun Wang

Crystals 2022, 12(2), 187; https://doi.org/10.3390/cryst12020187 - 27 Jan 2022

Cited by 5 | Viewed by 2112

Abstract

CdZnTe (CZT) films were grown by closed space sublimation (CSS) method on (111)-oriented CZT wafers, non-oriented CZT wafers and FTO substrates. The compositional and morphological properties of CZT films on different substrates were characterized by scanning electron microscopy (SEM) and atomic force microscopy [...] Read more.

CdZnTe (CZT) films were grown by closed space sublimation (CSS) method on (111)-oriented CZT wafers, non-oriented CZT wafers and FTO substrates. The compositional and morphological properties of CZT films on different substrates were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which indicated that CZT films grown on (111)-oriented CZT wafers had low dislocation density and high Zn composition. X-ray diffraction (XRD) measurements confirmed that CZT films grown on (111)-oriented CZT wafers had the best crystal quality. The I-V and DC photoconductivity measurements indicated that CZT films on (111)-oriented CZT wafer had good carrier transport performance. The energy spectra of CZT films grown on (111)-oriented CZT wafer presented that it had a good response to the nuclear radiation under ²⁴¹Am. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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8 pages, 2338 KiB

Open AccessArticle

The Influence of Ion Beam Bombardment on the Properties of High Laser-Induced Damage Threshold HfO₂ Thin Films

by Yingxue Xi, Jiwu Zhao, Jin Zhang, Changming Zhang and Qi Wu

Crystals 2022, 12(1), 117; https://doi.org/10.3390/cryst12010117 - 17 Jan 2022

Cited by 3 | Viewed by 1400

Abstract

HfO₂ thin films were deposited on BK-7 glass substrates using an electron beam evaporation deposition (EBD) technique and then post-treated with argon and oxygen ions at an ion energy ranging from 800 to 1200 eV. The optical properties, laser damage resistance, and [...] Read more.

HfO₂ thin films were deposited on BK-7 glass substrates using an electron beam evaporation deposition (EBD) technique and then post-treated with argon and oxygen ions at an ion energy ranging from 800 to 1200 eV. The optical properties, laser damage resistance, and surface morphology of the thin films exposed to Ar ions and O₂ ions at various energies were studied. It was found that the two ion post-treatment methods after deposition were effective for improving the LIDT of HfO₂ thin films, but the mechanism for the improvement differs. The dense thin films highly resistant to laser damage can be obtained through Ar ion post-treatment at a certain ion energy. The laser-induced damage threshold (LIDT) of thin films after O₂ ion post-treatment was higher in comparison to those irradiated with Ar ion at the same ion energy. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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12 pages, 1529 KiB

Open AccessArticle

Effect of Irradiation with Low-Energy He²⁺ Ions on Degradation of Structural, Strength and Heat-Conducting Properties of BeO Ceramics

by Maxim V. Zdorovets, Dmitriy I. Shlimas, Artem L. Kozlovskiy and Daryn B. Borgekov

Crystals 2022, 12(1), 69; https://doi.org/10.3390/cryst12010069 - 05 Jan 2022

Cited by 1 | Viewed by 1150

Abstract

The paper is devoted to the study of radiation-induced damage kinetics in beryllium oxide ceramics under irradiation with low-energy helium ions with fluences of 10¹⁵–10¹⁸ ion/cm². It was revealed that at irradiation fluences above 10¹⁷ ion/cm² [...] Read more.

The paper is devoted to the study of radiation-induced damage kinetics in beryllium oxide ceramics under irradiation with low-energy helium ions with fluences of 10¹⁵–10¹⁸ ion/cm². It was revealed that at irradiation fluences above 10¹⁷ ion/cm², a decrease in radiation-induced damage formation and accumulation rate is observed, which indicates the saturation effect. At the same time, the main mechanisms of structural changes caused by irradiation at these fluences are amorphization processes and dislocation density increase, while at fluences of 10¹⁵–10¹⁶ ion/cm², the main mechanisms of structural changes are due to the reorientation of crystallites and a change in texture, with a small contribution of crystal lattice distorting factors. It was discovered that the radiation-induced damage accumulation as well as an implanted helium concentration increase leads to the surface layer destruction, which is expressed in the ceramic surface hardness and wear resistance deterioration. It was determined that with irradiation fluences of 10¹⁵–10¹⁶ ion/cm², the decrease in thermal conductivity is minimal and is within the measurement error, while an increase in the irradiation fluence above 10¹⁷ ion/cm² leads to an increase in heat losses by more than 10%. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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12 pages, 5699 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Grain Boundaries on Crystal Structure and Tensile Mechanical Properties of Al_0.1CoCrFeNi High-Entropy Alloys Studied by Molecular Dynamics Method

by Cuixia Liu, Rui Wang and Zengyun Jian

Crystals 2022, 12(1), 48; https://doi.org/10.3390/cryst12010048 - 30 Dec 2021

Cited by 5 | Viewed by 2159

Abstract

The mechanical properties of high-entropy alloys are superior to those of traditional alloys. However, the key problem of finding a strengthening mechanism is still challenging. In this work, the molecular dynamics method is used to calculate the tensile properties of face-centered cubic Al [...] Read more.

The mechanical properties of high-entropy alloys are superior to those of traditional alloys. However, the key problem of finding a strengthening mechanism is still challenging. In this work, the molecular dynamics method is used to calculate the tensile properties of face-centered cubic Al_0.1CoCrFeNi high-entropy alloys containing Σ3 grain boundaries and without grain boundary. The atomic model was established by the melting rapid cooling method, then stretched by the static drawing method. The common neighbor analysis and dislocation extraction algorithm are used to analyze the crystal evolution mechanism of Σ3 grain boundaries to improve the material properties of high-entropy alloys during the tensile test. The results show that compared with the mechanical properties Al_0.1CoCrFeNi high-entropy alloys without grain boundary, the yield strength and Young’s modulus of a high-entropy alloy containing Σ3 grain boundary are obviously larger than that of high-entropy alloys without grain boundary. Dislocation type includes mainly 1/6<112> Shockley partial dislocations, a small account of 1/6<110> Stair-rod, 1/2<110>perfect dislocation, and 1/3<111> Hirth dislocations. The mechanical properties of high-entropy alloys are improved by dislocation entanglement and accumulation near the grain boundary. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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8 pages, 1119 KiB

Open AccessArticle

Evaluation of Relationship between Grain Morphology and Growth Temperature of HgI₂ Poly-Films for Direct Conversion X-ray Imaging Detectors

by Gang Xu, Ming Yao, Mingtao Zhang, Jinmeng Zhu, Yongxing Wei, Zhi Gu and Lan Zhang

Crystals 2022, 12(1), 32; https://doi.org/10.3390/cryst12010032 - 26 Dec 2021

Viewed by 1940

Abstract

The relationship between depositing temperature and crystallinity of grain for HgI₂ polycrystalline film with 170 cm² in area deposited by Physical Vapor Deposition (PVD) was investigated, considering the matches with readout matrix pixelation for female breast examination. The different depositing temperatures, [...] Read more.

The relationship between depositing temperature and crystallinity of grain for HgI₂ polycrystalline film with 170 cm² in area deposited by Physical Vapor Deposition (PVD) was investigated, considering the matches with readout matrix pixelation for female breast examination. The different depositing temperatures, 35, 40 and 45 °C, were carried out with the same source temperature, 100 °C, corresponding to 2–2.5 h of the growth period. The films deposited were investigated by XRD, SEM, and I–V. The results show that the grain size of the films grown increases with the depositing temperature from 35 to 45 °C. At 45 °C, the polycrystalline film has a preferred microcrystal orientation with 97.2% of [001]/[hkl] and grain size is about 180–220 μm. A 256 × 256 pixels X-ray image of a bolt, key, and wiring displacement was present distinctly with 50 keV with 6 mA current of X-ray generator. Our discussions on the relationship between depositing temperature and crystallinity of grain of film suggest that the higher growth temperature, the better crystallinity and excellent preferred microcrystal orientation of grain, however, with complementary bigger grain size. For matching readout matrix pixelation, the growth period of poly-films would be reduced appropriately for reasonable grain size and preventing the crack of films deposited. Full article

(This article belongs to the Special Issue Photovoltaic Functional Crystals and Ceramics)

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