Crystals

10 pages, 3439 KiB

Open AccessArticle

Single Source Precursor for PAD-LaMnO₃ Thin Films

by Ramona Bianca Sonher, Richard Attila Varga, Mircea Nasui, Traian Petrisor Jr, Mihai Sebastian Gabor, Marin Senila, Alessandro Rufoloni, Traian Petrisor and Lelia Ciontea

Crystals 2020, 10(9), 851; https://doi.org/10.3390/cryst10090851 - 22 Sep 2020

Viewed by 2880

Abstract

A new lanthanum and manganese ethylenediaminetetraacetate (EDTA) coordination polymer (EDTA⁴⁻ = [(CH₂N)₂(CH₂-COOH)(CH₂COO)₄]) was synthesized from La(NO₃)₃ and Mn(NO₃)₂ reagents, ethylenediaminetetraacetic acid, and water at room temperature. [...] Read more.

A new lanthanum and manganese ethylenediaminetetraacetate (EDTA) coordination polymer (EDTA⁴⁻ = [(CH₂N)₂(CH₂-COOH)(CH₂COO)₄]) was synthesized from La(NO₃)₃ and Mn(NO₃)₂ reagents, ethylenediaminetetraacetic acid, and water at room temperature. The structure of the new compound formed, [{La₂Mn₃(EDTA)₃(H₂O)₁₁}·12H₂O]_n, was determined by the single crystal X-ray diffraction technique. The synthesis and characterization of the La(III) and Mn(II) coordination complex, characterized by FTIR spectroscopy, thermogravimetry, and differential thermal analysis of the complex, are envisaged. X-ray crystal structure determination indicates that seven- and four-coordinate modes between La(III)/Mn(Π) and H₄EDTA exist. [{La₂Mn₃(EDTA)₃(H₂O)₁₁}·12H₂O]_n crystallizes in the monoclinic space group C2 with unit cell parameters of a = 16.1227(17) Å, b = 14.8049(16) Å, c = 14.8736(16) Å, and β = 116.107(2)°. Using this precursor, LaMnO₃ (LMO) epitaxial thin films were grown by the polymer-assisted deposition (PAD) method on (100)SrTiO₃ (STO) single crystalline substrates at a temperature of 900 °C. The LMO crystallized films exhibit a (001)LMO/(001)STO out-of-plane epitaxial relationship and a smooth surface morphology. Full article

(This article belongs to the Section Crystal Engineering)

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8 pages, 3618 KiB

Open AccessArticle

Grating Coupler Design for Vertical Light Coupling in Silicon Thin Films on Lithium Niobate

by Huangpu Han and Bingxi Xiang

Crystals 2020, 10(9), 850; https://doi.org/10.3390/cryst10090850 - 22 Sep 2020

Cited by 6 | Viewed by 3798

Abstract

In this paper we provide a design for a vertical grating coupler for a silicon thin film on lithium niobate. The parameters-such as the cladding layer thickness of lithium niobate, fiber position, fiber angle, grating period, and duty cycle are analyzed and optimized [...] Read more.

In this paper we provide a design for a vertical grating coupler for a silicon thin film on lithium niobate. The parameters-such as the cladding layer thickness of lithium niobate, fiber position, fiber angle, grating period, and duty cycle are analyzed and optimized to reduce the mode mismatch loss and the internal reflections. The alignment tolerances, for the grating coupler parameters, are also simulated and evaluated. We determine that our simulated grating coupler exhibits high efficiency, enhanced light coupling, and high alignment tolerance. Full article

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12 pages, 3644 KiB

Open AccessArticle

A Multifaceted Kinetic Model for the Thermal Decomposition of Calcium Carbonate

by Jingxue Zheng, Junchen Huang, Lin Tao, Zhi Li and Qi Wang

Crystals 2020, 10(9), 849; https://doi.org/10.3390/cryst10090849 - 22 Sep 2020

Cited by 14 | Viewed by 4996

Abstract

The existing kinetic models often consider the influence of a single factor alone on the chemical reaction and this is insufficient to completely describe the decomposition reaction of solids. Therefore, the existing kinetic models were improved using the pore structure model. The proposed [...] Read more.

The existing kinetic models often consider the influence of a single factor alone on the chemical reaction and this is insufficient to completely describe the decomposition reaction of solids. Therefore, the existing kinetic models were improved using the pore structure model. The proposed model was verified using the thermal decomposition experiment on calcium carbonate. The equation has been modified as

f (α) = n {(1 - α)}^{1 - \frac{1}{n}} {[- l n (1 - α)]}^{- \frac{1}{m}} {[1 - ψ l n (1 - α)]}^{\frac{1}{2}}

. This led to the conclusion that the pore structure, generated during the thermal decomposition of calcite, has an important influence on the decomposition kinetics. The existing experimental data show that the improved model, with random pores as the main body, reasonably describes the thermal decomposition process of calcite. Full article

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7 pages, 1502 KiB

Open AccessArticle

Effects of GaN Buffer Resistance on the Device Performances of AlGaN/GaN HEMTs

by Ki-Sik Im, Jae-Hoon Lee, Yeo Jin Choi and Sung Jin An

Crystals 2020, 10(9), 848; https://doi.org/10.3390/cryst10090848 - 22 Sep 2020

Cited by 7 | Viewed by 3945

Abstract

We investigated the effects of GaN buffer resistance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on direct current (DC), low-frequency noise (LFN), and pulsed I-V characterization performances. The devices with the highest GaN buffer resistance were grown on sapphire substrate using two-step growth [...] Read more.

We investigated the effects of GaN buffer resistance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on direct current (DC), low-frequency noise (LFN), and pulsed I-V characterization performances. The devices with the highest GaN buffer resistance were grown on sapphire substrate using two-step growth temperature method without additional compensation doping. The proposed device exhibited the degraded off-state leakage current due to the improved GaN buffer quality compared to the reference devices with relative low buffer resistance, which is confirmed by high resolution X-ray diffraction (HRXRD). However, the proposed device with deep-level defects in GaN buffer layer showed the reduced hysteresis (∆V_th), increased breakdown voltage (BV), and enhanced pulse I-V characteristics. Regardless of GaN buffer resistance, all devices clearly showed 1/f behavior with carrier number fluctuations (CNF) at on-state but followed 1/f² characteristic at off-state. From the 1/f² noise characteristics, the extracted trap time constant (τ_i) of the proposed device can be obtained to be 10 ms, which is shorter than those of the reference devices because of the full compensation of deep-level defects in the GaN buffer layer. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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12 pages, 2638 KiB

Open AccessArticle

Characterization of Accumulated B-Integral of Regenerative Amplifier Based CPA Systems

by Stefan Bock, Franziska Marie Herrmann, Thomas Püschel, Uwe Helbig, René Gebhardt, Jakob Johannes Lötfering, Richard Pausch, Karl Zeil, Tim Ziegler, Arie Irman, Thomas Oksenhendler, Akira Kon, Mamiko Nishuishi, Hiromitsu Kiriyama, Kiminori Kondo, Toma Toncian and Ulrich Schramm

Crystals 2020, 10(9), 847; https://doi.org/10.3390/cryst10090847 - 22 Sep 2020

Cited by 8 | Viewed by 5910

Abstract

We report on a new approach to measure the accumulated B-integral in the regenerative and multipass amplifier stages of ultrashort-pulse high-power laser systems by B-integral-induced coupling between delayed test post-pulses and the main pulse. A numerical model for such non-linear pulse coupling is [...] Read more.

We report on a new approach to measure the accumulated B-integral in the regenerative and multipass amplifier stages of ultrashort-pulse high-power laser systems by B-integral-induced coupling between delayed test post-pulses and the main pulse. A numerical model for such non-linear pulse coupling is presented and compared to data taken at the high-power laser Draco with self-referenced spectral interferometry (SRSI). The dependence of the B-integral accumulated in the regenerative amplifier on its operation mode enables optimization strategies for extracted energy vs. collected B-integral. The technique presented here can, in principle, be applied to characterize any type of ultrashort pulse laser system and is essential for pre-pulse reduction. Full article

(This article belongs to the Special Issue Development of High Intensity Crystal Laser and Its Applications)

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11 pages, 4435 KiB

Open AccessArticle

Si Quantum Dots Assist Synthesized Microflower-Like Si/MoS₂ Composites for Supercapacitors

by Jiahong Zheng, Kangkang Cheng, Runmei Zhang, Yamei Yang, Yuntao Wu and Pengfei Yu

Crystals 2020, 10(9), 846; https://doi.org/10.3390/cryst10090846 - 22 Sep 2020

Cited by 3 | Viewed by 2359

Abstract

The microflower-like Si/MoS₂ composites were fabricated using Si quantum dots (QDs) to assist a facile hydrothermal method. The electrochemical performance of Si/MoS₂ composite in symmetric and asymmetric systems was studied. Electrochemical characterization revealed that the Si/MoS₂ composite electrode in a [...] Read more.

The microflower-like Si/MoS₂ composites were fabricated using Si quantum dots (QDs) to assist a facile hydrothermal method. The electrochemical performance of Si/MoS₂ composite in symmetric and asymmetric systems was studied. Electrochemical characterization revealed that the Si/MoS₂ composite electrode in a three-electrode system has a high specific capacitance of 574.4 F·g⁻¹ at 5 A·g⁻¹. Furthermore, the Si/MoS₂ composite electrode in a two-electrode system had the maximum energy density of 27.2 Wh·kg⁻¹ when a power density of 749.1 W·kg⁻¹ was achieved. Therefore, this investigation proves the Si/MoS₂ composite microflower-like structure should be a promising candidate electrode material for supercapacitors. Full article

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16 pages, 3409 KiB

Open AccessEditor’s ChoiceArticle

Depth Profile Analysis of Deep Level Defects in 4H-SiC Introduced by Radiation

by Tomislav Brodar, Luka Bakrač, Ivana Capan, Takeshi Ohshima, Luka Snoj, Vladimir Radulović and Željko Pastuović

Crystals 2020, 10(9), 845; https://doi.org/10.3390/cryst10090845 - 22 Sep 2020

Cited by 9 | Viewed by 5528

Abstract

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below [...] Read more.

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below the conduction band minimum are created in either ion implanted and neutron irradiated material beside carbon vacancies (Z_1/2). In our study, we analyze components of EH1 and EH3 deep levels based on their concentration depth profiles, in addition to (−3/=) and (=/−) transition levels of silicon vacancy. A higher EH3 deep level concentration compared to the EH1 deep level concentration and a slight shift of the EH3 concentration depth profile to larger depths indicate that an additional deep level contributes to the DLTS signal of the EH3 deep level, most probably the defect complex involving interstitials. We report on the introduction of metastable M-center by light/medium heavy ion implantation and neutron irradiation, previously reported in cases of proton and electron irradiation. Contribution of M-center to the EH1 concentration profile is presented. Full article

(This article belongs to the Special Issue Crystalline Materials for Radiation Detection: A New Perspectives)

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9 pages, 3566 KiB

Open AccessArticle

Proton, UV, and X-ray Induced Luminescence in Tb³⁺ Doped LuGd₂Ga₂Al₃O₁₂ Phosphors

by U. Fawad, H. J. Kim, Ibrahim Gul, Matiullah Khan, Sajjad Tahir, Tauseef Jamal and Wazir Muhammad

Crystals 2020, 10(9), 844; https://doi.org/10.3390/cryst10090844 - 22 Sep 2020

Cited by 7 | Viewed by 2798

Abstract

The well-known solid-state reaction method is used for the synthesis of Tb doped LuGd₂Ga₂Al₃O₁₂ phosphor. XRD and SEM techniques are used for the phase and structural morphology of the synthesized phosphor. UV, X-ray and proton induced [...] Read more.

The well-known solid-state reaction method is used for the synthesis of Tb doped LuGd₂Ga₂Al₃O₁₂ phosphor. XRD and SEM techniques are used for the phase and structural morphology of the synthesized phosphor. UV, X-ray and proton induced spectroscopy is used to study the luminescence properties. LuGd₂Ga₂Al₃O₁₂:Tb³⁺ phosphor shows its highest peak in green and blue region. The two major emission peaks correspond to ⁵D₃→⁷F_J (at 480 to 510 nm, blue region) and ⁵D₄→⁷F_J (at 535 to 565 nm, green region). Green emission is dominant; therefore, it may be used as an efficient green phosphor. The absorption spectra of the synthesized material matches well with the spectra of light emitting diodes (LEDs); therefore, it may have applications in LEDs. X-ray spectroscopic study suggests that this phosphor may have uses in medical applications, such as X-ray imaging. The synthesized phosphor exhibits 81% efficacy in comparison to the commercial plasma display panel material (Gd₂O₂S:Tb³⁺). The Commission Internationale de l’Eclairage (CIE) chromaticity diagram is obtained for this phosphor. The decay time of ms range is measured for the synthesized phosphor. Full article

(This article belongs to the Special Issue Xene Materials and Biomedical Applications of Nanostructures)

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19 pages, 4490 KiB

Open AccessReview

Spin Crossover in New Iron(II) Coordination Compounds with Tris(pyrazol-1-yl)Methane

by Olga G. Shakirova and Ludmila G. Lavrenova

Crystals 2020, 10(9), 843; https://doi.org/10.3390/cryst10090843 - 22 Sep 2020

Cited by 26 | Viewed by 3691

Abstract

We review here new advances in the synthesis and investigation of iron(II) coordination compounds with tris(pyrazol-1-yl)methane and its derivatives as ligands. The complexes demonstrate thermally induced spin crossover accompanied by thermochromism. Factors that influence the nature and temperature of the spin crossover are [...] Read more.

We review here new advances in the synthesis and investigation of iron(II) coordination compounds with tris(pyrazol-1-yl)methane and its derivatives as ligands. The complexes demonstrate thermally induced spin crossover accompanied by thermochromism. Factors that influence the nature and temperature of the spin crossover are discussed. Full article

(This article belongs to the Special Issue Coordination Polymers)

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13 pages, 6369 KiB

Open AccessArticle

Development of Catalytic-CVD SiN_x Passivation Process for AlGaN/GaN-on-Si HEMTs

by Myoung-Jin Kang, Hyun-Seop Kim, Ho-Young Cha and Kwang-Seok Seo

Crystals 2020, 10(9), 842; https://doi.org/10.3390/cryst10090842 - 21 Sep 2020

Cited by 10 | Viewed by 4731

Abstract

We optimized a silicon nitride (SiN_x) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiN_x film exhibited a high film density of 2.7 [...] Read more.

We optimized a silicon nitride (SiN_x) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiN_x film exhibited a high film density of 2.7 g/cm³ with a low wet etch rate (buffered oxide etchant (BOE) 10:1) of 2 nm/min and a breakdown field of 8.2 MV/cm. The AlGaN/GaN-on-Si HEMT fabricated by the optimized Cat-CVD SiN_x passivation process, which had a gate length of 1.5 μm and a source-to-drain distance of 6 μm, exhibited the maximum drain current density of 670 mA/mm and the maximum transconductance of 162 mS/mm with negligible hysteresis. We found that the optimized SiN_x film had positive charges, which were responsible for suppressing the current collapse phenomenon. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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9 pages, 2492 KiB

Open AccessArticle

Gas-Dependent Reversible Structural and Magnetic Transformation between Two Ladder Compounds

by Jun Manabe, Kazuki Nishida, Xiao Zhang, Yuki Nakano, Masaru Fujibayashi, Goulven Cosquer, Katsuya Inoue, Seiya Shimono, Hiroki Ishibashi, Yoshiki Kubota, Misaki Shiga, Ryo Tsunashima, Yoko Tatewaki and Sadafumi Nishihara

Crystals 2020, 10(9), 841; https://doi.org/10.3390/cryst10090841 - 19 Sep 2020

Cited by 2 | Viewed by 3084

Abstract

We report reversible structural transformation that occurs in two ladder compounds: Cu₂CO₃(ClO₄)₂(NH₃)₆ (1) and Cu₂CO₃(ClO₄)₂(NH₃)₅(H₂O) ( [...] Read more.

We report reversible structural transformation that occurs in two ladder compounds: Cu₂CO₃(ClO₄)₂(NH₃)₆ (1) and Cu₂CO₃(ClO₄)₂(NH₃)₅(H₂O) (2), when they are exposed to gaseous vapors. The ladder structures of both 1 and 2 consist of two Cu²⁺ ions and one CO₃²⁻ ion. In 1, the Cu²⁺ ions are coordinated by three NH₃ molecules on each side, while those in 2 are coordinated by three NH₃ molecules on one side, and two NH₃ molecules and one H₂O molecule on the other side. We demonstrated reversible transformation of 1 and 2 via the exposure of 1 to H₂O vapor and the exposure of 2 to NH₃ vapor using a simple bench-scale method. The minor structural change observed led to a significant difference in physical properties, which we observed using several methods. Full article

(This article belongs to the Special Issue Organic Conductors)

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17 pages, 8472 KiB

Open AccessArticle

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

by Inge Nys, Brecht Berteloot and Guilhem Poy

Crystals 2020, 10(9), 840; https://doi.org/10.3390/cryst10090840 - 19 Sep 2020

Cited by 21 | Viewed by 4010

Abstract

Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design [...] Read more.

Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design of the alignment patterns allows the stabilization of topological solitons in nematic liquid crystal (NLC) cells, without the need for chirality or strong confinement. The created LC configurations are stabilized by the anchoring conditions imposed at the substrates. The photo-aligned background at both substrates is uniformly planar aligned, and ring-shaped regions with a 180° azimuthal rotation are patterned with an opposite sense of rotation at the top and bottom substrate. A disclination-free structure containing a closed ring of vertically oriented directors is formed when the patterned rings at the top and bottom substrate overlap. Thanks to the topological stability, a vertical director orientation in the bulk is observed even when the centra of both patterned rings are shifted over relatively large distances. The combination of numerical simulations with experimental measurements allows identification of the 3D director configuration in the bulk. A finite element (FE) Q-tensor simulation model is applied to find the equilibrium director configuration and optical simulations are used to confirm the correspondence with experimental microscopy measurements. The created LC configurations offer opportunities in the field of optical devices, light guiding and switching, particle trapping and studies of topological LC structures. Full article

(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment (Volume II))

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32 pages, 4946 KiB

Open AccessArticle

A Nature’s Curiosity: The Argonaut “Shell” and Its Organic Content

by Morgane Oudot, Ira Ben Shir, Asher Schmidt, Laurent Plasseraud, Cédric Broussard, Pascal Neige and Frédéric Marin

Crystals 2020, 10(9), 839; https://doi.org/10.3390/cryst10090839 - 19 Sep 2020

Cited by 10 | Viewed by 4333

Abstract

Molluscs are known for their ability to produce a calcified shell resulting from a genetically controlled and matrix-mediated process, performed extracellularly. The occluded organic matrix consists of a complex mixture of proteins, glycoproteins and polysaccharides that are in most cases secreted by the [...] Read more.

Molluscs are known for their ability to produce a calcified shell resulting from a genetically controlled and matrix-mediated process, performed extracellularly. The occluded organic matrix consists of a complex mixture of proteins, glycoproteins and polysaccharides that are in most cases secreted by the mantle epithelium. To our knowledge, the model studied here—the argonaut, also called paper nautilus—represents the single mollusc example where this general scheme is not valid: the shell of this cephalopod is indeed formed by its first dorsal arms pair and it functions as an eggcase, secreted by females only; furthermore, this coiled structure is fully calcitic and the organization of its layered microstructures is unique. Thus, the argonautid shell appears as an apomorphy of this restricted family, not homologous to other cephalopod shells. In the present study, we investigated the physical and biochemical properties of the shell of Argonauta hians, the winged argonaut. We show that the shell matrix contains unusual proportions of soluble and insoluble components, and that it is mostly proteinaceous, with a low proportion of sugars that appear to be mostly sulfated glycosaminoglycans. Proteomics performed on different shell fractions generated several peptide sequences and identified a number of protein hits, not shared with other molluscan shell matrices. This may suggest the recruitment of unique molecular tools for mineralizing the argonaut’s shell, a finding that has some implications on the evolution of cephalopod shell matrices. Full article

(This article belongs to the Special Issue Biominerals: Formation, Function, Properties)

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10 pages, 2102 KiB

Open AccessArticle

Ti₃O₅ and Al₂TiO₅ Crystals Flotation Characteristics from Ti-bearing Blast Furnace Slag: A Density Functional Theory and Experimental Study

by Shan Ren, Zenghui Su, Weizao Liu, Yali Sun, Xiaoming Li and Jian Yang

Crystals 2020, 10(9), 838; https://doi.org/10.3390/cryst10090838 - 19 Sep 2020

Cited by 5 | Viewed by 3150

Abstract

Anosovite crystalline is an ideal mineral for flotation from the Ti-bearing blast furnace (TBBF) slag. Ti₃O₅ crystal and Al₂TiO₅ crystal are two kinds of anosovites, and the Al element significantly affects the electronic structure and flotation performance [...] Read more.

Anosovite crystalline is an ideal mineral for flotation from the Ti-bearing blast furnace (TBBF) slag. Ti₃O₅ crystal and Al₂TiO₅ crystal are two kinds of anosovites, and the Al element significantly affects the electronic structure and flotation performance of anosovite. The floatability of Ti₃O₅ and Al₂TiO₅ crystals were studied by Mulliken populations, energy bands, and density of states (DOS). In addition, the flotation experiment of the two kinds of anosovite crystals (Ti₃O₅ and Al₂TiO₅) was conducted and proved that the density functional theory (DFT) calculation results were accurate. Compared with Ti₃O₅ crystal, the Fermi energy level of Al₂TiO₅ crystal shifts around 2 eV in a negative direction by DOS analysis, which is beneficial to flotation. And Al₂TiO₅ crystal possesses a larger value of bond population, which is 0.41, for Ti-O bonds than Ti₃O₅ crystal and the bond length of Ti-O in Al₂TiO₅ crystal is shorter, therefore Al₂TiO₅ crystal shows a stronger covalency. The changes of the Fermi energy level and the covalency bonds in Al₂TiO₅ crystal both demonstrated that doping the Al component into the Ti₃O₅ crystal was beneficial to improve the flotation effect. Moreover, the Al₂TiO₅ crystal had a higher flotation efficiency compared to the Ti₃O₅ crystal when the dosages of salicylhydroxamic acid (SHA) and sodium oleate were the same. Therefore, both DFT calculation and experiment show that the flotation effect of the Al₂TiO₅ crystal is better than that of the Ti₃O₅ crystal. Full article

(This article belongs to the Special Issue Metallurgical Slag)

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10 pages, 14044 KiB

Open AccessArticle

High-Intensity Laser-Driven Oxygen Source from CW Laser-Heated Titanium Tape Targets

by Kotaro Kondo, Mamiko Nishiuchi, Hironao Sakaki, Nicholas P. Dover, Hazel F. Lowe, Takumi Miyahara, Yukinobu Watanabe, Tim Ziegler, Karl Zeil, Ulrich Schramm, Emma J. Ditter, George S. Hicks, Oliver C. Ettlinger, Zulfikar Najmudin, Hiromitsu Kiriyama, Masaki Kando and Kiminori Kondo

Crystals 2020, 10(9), 837; https://doi.org/10.3390/cryst10090837 - 19 Sep 2020

Cited by 5 | Viewed by 4883

Abstract

The interaction of high-intensity laser pulses with solid targets can be used as a highly charged, energetic heavy ion source. Normally, intrinsic contaminants on the target surface suppress the performance of heavy ion acceleration from a high-intensity laser–target interaction, resulting in preferential proton [...] Read more.

The interaction of high-intensity laser pulses with solid targets can be used as a highly charged, energetic heavy ion source. Normally, intrinsic contaminants on the target surface suppress the performance of heavy ion acceleration from a high-intensity laser–target interaction, resulting in preferential proton acceleration. Here, we demonstrate that CW laser heating of 5 µm titanium tape targets can remove contaminant hydrocarbons in order to expose a thin oxide layer on the metal surface, ideal for the generation of energetic oxygen beams. This is demonstrated by irradiating the heated targets with a PW class high-power laser at an intensity of 5 × 10²¹ W/cm², showing enhanced acceleration of oxygen ions with a non-thermal-like distribution. Our new scheme using a CW laser-heated Ti tape target is promising for use as a moderate repetition energetic oxygen ion source for future applications. Full article

(This article belongs to the Special Issue Development of High Intensity Crystal Laser and Its Applications)

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17 pages, 4038 KiB

Open AccessArticle

Effect of Nitrogen Content on the Formation of Inclusions in Fe-5Mn-3Al Steels

by Michelia Alba, Muhammad Nabeel and Neslihan Dogan

Crystals 2020, 10(9), 836; https://doi.org/10.3390/cryst10090836 - 18 Sep 2020

Cited by 8 | Viewed by 2725

Abstract

The effect of N content on the characteristics and formation of inclusions in the Fe-5Mn-3Al steels was investigated in this study. Two synthetic steel melts were produced by two different methods—N₂ gas purging and injecting—to introduce nitrogen into the melt. The N [...] Read more.

The effect of N content on the characteristics and formation of inclusions in the Fe-5Mn-3Al steels was investigated in this study. Two synthetic steel melts were produced by two different methods—N₂ gas purging and injecting—to introduce nitrogen into the melt. The N content of steel melt varied from 2 to 54 ppm. An increase in the N content to 47 ppm (for 533N-P) and 58 ppm (for 533N-I) increased the total amount of inclusions from 13 to 64 mm⁻² and from 21 to 101 mm⁻², respectively. The observed inclusions were Al₂O_3(pure), Al₂O₃-MnS, AlN_(pure), AlN-MnS, AlON, AlON-MnS, and MnS. When the N content was less than 10 ppm, AlN-MnS inclusions were the primary type of inclusions and they formed as solidification products. With an increase in the N content, AlN_(pure) inclusions became the dominant type of inclusions as AlN was stable in the liquid steel. These findings were confirmed by thermodynamic calculations. The influence of cooling rate on the types of inclusions was studied and a higher number of AlN-MnS inclusions were observed in samples with slow cooling rate. Full article

(This article belongs to the Special Issue Liquid Steel Alloying Process)

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14 pages, 2400 KiB

Open AccessArticle

Engineering Aspheric Liquid Crystal Lenses by Using the Transmission Electrode Technique

by José Francisco Algorri, Dimitrios C. Zografopoulos, Luis Rodríguez-Cobo, José Manuel Sánchez-Pena and José Miguel López-Higuera

Crystals 2020, 10(9), 835; https://doi.org/10.3390/cryst10090835 - 18 Sep 2020

Cited by 16 | Viewed by 3060

Abstract

The transmission electrode technique has been recently proposed as a versatile method to obtain various types of liquid-crystal (LC) lenses. In this work, an equivalent electric circuit and new analytical expressions based on this technique are developed. In addition, novel electrode shapes are [...] Read more.

The transmission electrode technique has been recently proposed as a versatile method to obtain various types of liquid-crystal (LC) lenses. In this work, an equivalent electric circuit and new analytical expressions based on this technique are developed. In addition, novel electrode shapes are proposed in order to generate different phase profiles. The analytical expressions depend on manufacturing parameters that have been optimized by using the least squares method. Thanks to the proposed design equations and the associated optimization, the feasibility of engineering any kind of aspheric LC lenses is demonstrated, which is key to obtain aberration-free lenses. The results are compared to numerical simulations validating the proposed equations. This novel technique, in combination with the proposed design equations, opens a new path for the design and fabrication of LC lenses and even other types of adaptive-focus lenses based on voltage control. Full article

(This article belongs to the Special Issue Patterned-Liquid-Crystal for Novel Displays)

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21 pages, 1053 KiB

Open AccessArticle

Dual-Energy X-ray Medical Imaging with Inverse Compton Sources: A Simulation Study

by Gianfranco Paternò, Paolo Cardarelli, Mauro Gambaccini and Angelo Taibi

Crystals 2020, 10(9), 834; https://doi.org/10.3390/cryst10090834 - 18 Sep 2020

Cited by 11 | Viewed by 3669

Abstract

It has been long recognized that dual-energy imaging could help to enhance the detectability of lesions in diagnostic radiology, by removing the contrast of surrounding tissues. Furthermore, X-ray attenuation is material specific and information about the object constituents can be extracted for tissue [...] Read more.

It has been long recognized that dual-energy imaging could help to enhance the detectability of lesions in diagnostic radiology, by removing the contrast of surrounding tissues. Furthermore, X-ray attenuation is material specific and information about the object constituents can be extracted for tissue characterisation, i.e., to assess whether lesions represent a malignant or benign process. However, a true separation between the low and high energy components is not possible with conventional sources because of their broad X-ray spectrum, and the artifacts produced in the subtracted image can be only partially removed. Finally, dose issues have also prevented so far the application of dual-energy techniques within the clinical context. Very recently, a new intense and monochromatic X-ray source was proposed to fill the gap between a synchrotron radiation facility and the standard X-ray tube. Indeed, inverse Compton scattering (ICS) sources, which are based on the interaction of a powerful laser beam and a bright beam of relativistic electrons, are among the most promising innovative sources of monochromatic X and gamma radiation. In this contribution, we review the main features that allow an ICS source to meet the requirements of a medical imaging application. Specific examples of K-edge subtraction are then provided, to show the potential of ICS in clinical applications that require intravenous injection of a contrast medium. Full article

(This article belongs to the Special Issue Development and Application of Novel Dual Energy X-ray Imaging Methods)

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13 pages, 2803 KiB

Open AccessArticle

Microwave-Assisted Aldol Condensation of Furfural and Acetone over Mg–Al Hydrotalcite-Based Catalysts

by Alberto Tampieri, Matea Lilic, Magda Constantí and Francesc Medina

Crystals 2020, 10(9), 833; https://doi.org/10.3390/cryst10090833 - 18 Sep 2020

Cited by 16 | Viewed by 4480

Abstract

The depletion of fossil fuel resources has prompted the scientific community to find renewable alternatives for the production of energy and chemicals. The products of the aldol condensation between bio-based furfural and acetone have been individuated as promising intermediates for the preparation of [...] Read more.

The depletion of fossil fuel resources has prompted the scientific community to find renewable alternatives for the production of energy and chemicals. The products of the aldol condensation between bio-based furfural and acetone have been individuated as promising intermediates for the preparation of biofuels and polymeric materials. We developed a protocol for the microwave-assisted condensation of these two compounds over hydrotalcite-based materials. Mg:Al 2:1 hydrotalcite was prepared by co-precipitation; the obtained solid was calcined to afford the corresponding mixed metal oxide, which was then rehydrated to obtain a meixnerite-type material. The prepared solids were characterized by PXRD, ICP-AES, TGA-DSC and N₂ physisorption, and tested as catalysts in the aldol condensation of acetone and furfural in a microwave reactor. The performance of the catalysts was assessed and compared; the meixnerite catalyst proved to be the most active, followed by the mixed metal oxide and the as-synthesized hydrotalcite, which has often been reported to be inactive. In all cases, the reaction is quite fast and selective, which makes our protocol useful for rapidly converting furfural and acetone into their condensation products. Full article

(This article belongs to the Special Issue Layered Double Hydroxides (LDHs))

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4 pages, 183 KiB

Open AccessEditorial

Cement-Based Composites: Advancements in Development and Characterization

by Pawel Sikora and Sang-Yeop Chung

Crystals 2020, 10(9), 832; https://doi.org/10.3390/cryst10090832 - 17 Sep 2020

Cited by 7 | Viewed by 2497

Abstract

This Special Issue on “Cement-Based Composites: Advancements in Development and Characterization” presents the latest research and advances in the field of cement-based composites. This special issue covers a variety of experimental studies related to fibre-reinforced, photocatalytic, lightweight, and sustainable cement-based composites. Moreover, simulation [...] Read more.

This Special Issue on “Cement-Based Composites: Advancements in Development and Characterization” presents the latest research and advances in the field of cement-based composites. This special issue covers a variety of experimental studies related to fibre-reinforced, photocatalytic, lightweight, and sustainable cement-based composites. Moreover, simulation studies are present in this special issue to provide the fundamental knowledge on designing and optimizing the properties of cementitious composites. The presented publications in this special issue show the most recent technology in the cement-based composite field. Full article

(This article belongs to the Special Issue Cement-Based Composites: Advancements in Development and Characterization)

9 pages, 3674 KiB

Open AccessArticle

High-Thermal-Conductivity SiC Ceramic Mirror for High-Average-Power Laser System

by Yasuhiro Miyasaka, Kotaro Kondo and Hiromitsu Kiriyama

Crystals 2020, 10(9), 831; https://doi.org/10.3390/cryst10090831 - 17 Sep 2020

Cited by 1 | Viewed by 3531

Abstract

The importance of heat-resistant optics is increasing together with the average power of high-intensity lasers. A silicon carbide (SiC) ceramic with high thermal conductivity is proposed as an optics substrate to suppress thermal effects. The temperature rise of the substrate and the change [...] Read more.

The importance of heat-resistant optics is increasing together with the average power of high-intensity lasers. A silicon carbide (SiC) ceramic with high thermal conductivity is proposed as an optics substrate to suppress thermal effects. The temperature rise of the substrate and the change in the surface accuracy of the mirror surface, which degrades the laser beam quality, are investigated. Gold mirrors on synthetic fused silica and SiC ceramic substrates are heated with a 532 nm wavelength laser diode. The synthetic fused silica substrate placed on an aluminum block shows a temperature increase by ~32 °C and a large temperature gradient. In contrast, the SiC ceramic substrate shows a uniform temperature distribution and a temperature increase of only ~4 °C with an absorbed power of ~2 W after 20 min laser irradiation. The surface accuracy (roughness) when using the synthetic fused silica substrate changes from /21.8 (29.0 nm) to /7.2 (88.0 nm), increasing by a factor of ~3.0. However, that of the SiC ceramic substrate changes from /21.0 (30.2 nm) to /13.3 (47.7 nm), increasing by only a factor of ~1.6. Based on these experimental results, detailed considerations and calculations of actively cooled SiC ceramic substrates for high-average-power laser systems are also discussed. Full article

(This article belongs to the Special Issue Development of High Intensity Crystal Laser and Its Applications)

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7 pages, 1466 KiB

Open AccessArticle

Low-Frequency Noise Behavior of AlGaN/GaN HEMTs with Different Al Compositions

by Yeo Jin Choi, Jae-Hoon Lee, Sung Jin An and Ki-Sik Im

Crystals 2020, 10(9), 830; https://doi.org/10.3390/cryst10090830 - 17 Sep 2020

Cited by 10 | Viewed by 3171

Abstract

Al_xGa_1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray [...] Read more.

Al_xGa_1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray diffraction (HRXRD). Al_xGa_1−xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using the Hall effect, direct current (DC), and low-frequency noise (LFN). The device with high Al composition (28%) showed improved sheet resistance (R_sh) due to enhanced carrier confinement and reduced gate leakage currents caused by increased Schottky barrier height (SBH). On the other hand, the reduced noise level and the low trap density (N_t) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the Al_xGa_1−xN barrier layer according to the declined Al composition. In spite of the Al composition, the fabricated devices exhibited 1/ƒ noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (S_Id/I_d²) versus (g_m/I_d)² and (S_Id/I_d²) versus (V_gs–V_th). Although low Al composition is favorable to the reduced noise, it causes some problems like low R_sh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties. Full article

(This article belongs to the Special Issue Nano/Micro and Bio-Inspired Materials on Wide-Bandgap-Semiconductor-Based Optoelectronic/Power Devices)

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2 pages, 147 KiB

Open AccessEditorial

Synthesis and Characterization of Ferroelectrics

by Jan Dec

Crystals 2020, 10(9), 829; https://doi.org/10.3390/cryst10090829 - 17 Sep 2020

Viewed by 1696

Abstract

Ferroelectrics belong to one of the most studied groups of materials in terms of research and applications [...] Full article

(This article belongs to the Special Issue Synthesis and Characterization of Ferroelectrics)

15 pages, 3652 KiB

Open AccessArticle

Guided Crystallization of Zeolite Beads Composed of ZSM-12 Nanosponges

by Kassem Moukahhal, Ludovic Josien, Habiba Nouali, Joumana Toufaily, Tayssir Hamieh, T. Jean Daou and Bénédicte Lebeau

Crystals 2020, 10(9), 828; https://doi.org/10.3390/cryst10090828 - 17 Sep 2020

Cited by 1 | Viewed by 4222

Abstract

The direct route using a bifunctional amphiphilic structuring agent for the synthesis of hierarchical nanozeolites coupled with pseudomorphic transformation was used for the crystallization of hierarchized zeolite beads/hollow spheres composed of ZSM-12 (MTW structural-type) with nanosponge morphology. These beads/hollow spheres have the same [...] Read more.

The direct route using a bifunctional amphiphilic structuring agent for the synthesis of hierarchical nanozeolites coupled with pseudomorphic transformation was used for the crystallization of hierarchized zeolite beads/hollow spheres composed of ZSM-12 (MTW structural-type) with nanosponge morphology. These beads/hollow spheres have the same average diameter of 20 µm as their counterpart amorphous mesoporous silica beads used as precursor in the starting synthesis mixture. The effects of synthesis parameters, such as stirring and treatment time at 140 °C, on the morphology, structure, and texture of the materials have been investigated using X-ray diffraction (XRD), N₂ sorption, scanning electronic microscopy (SEM), and transmission electronic microscopy (TEM) techniques. Static conditions were found necessary to maintain the morphology of the starting amorphous silica beads. An Ostwald ripening phenomenon was observed with the increase in hydrothermal treatment time leading to the dissolution of the interior of some beads to form core shell beads or hollow spheres with larger crystals on the outer surface. These ZSM-12 beads/hollow spheres possess higher porous volume than conventional ZSM-12 zeolite powder and can be used directly for industrial applications. Full article

(This article belongs to the Special Issue Zeolites)

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13 pages, 5532 KiB

Open AccessArticle

Crystal Growth by the Floating Zone Method of Ce-Substituted Crystals of the Topological Kondo Insulator SmB₆

by Monica Ciomaga Hatnean, Talha Ahmad, Marc Walker, Martin R. Lees and Geetha Balakrishnan

Crystals 2020, 10(9), 827; https://doi.org/10.3390/cryst10090827 - 17 Sep 2020

Cited by 4 | Viewed by 3009

Abstract

SmB

_{6}

is a mixed valence topological Kondo insulator. To investigate the effect of substituting Sm with magnetic Ce ions on the physical properties of samarium hexaboride, Ce-substituted SmB

_{6}

crystals were grown by the floating zone method for the first time as [...] Read more.

SmB

_{6}

is a mixed valence topological Kondo insulator. To investigate the effect of substituting Sm with magnetic Ce ions on the physical properties of samarium hexaboride, Ce-substituted SmB

_{6}

crystals were grown by the floating zone method for the first time as large, good quality single crystal boules. The crystal growth conditions are reported. Structural, magnetic and transport properties of single crystals of Sm

_{1 - x}

Ce

_{x}

B

_{6}

(

x = 0.05

, 0.10 and 0.20) were investigated using X-ray diffraction techniques, electrical resistivity and magnetisation measurements. Phase composition analysis of the powder X-ray diffraction data collected on the as-grown boules revealed that the main phase was that of the parent compound, SmB

_{6}

. Substitution of Sm ions with magnetic Ce ions does not lead to long-range magnetic ordering in the

{Sm}_{1 - x} {Ce}_{x} B_{6}

crystals. The substitution with 5% Ce and above suppresses the cross-over from bulk conductivity at high temperatures to surface-only conductivity at low temperatures. Full article

(This article belongs to the Special Issue Advances in Topological Materials)

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12 pages, 7160 KiB

Open AccessArticle

Thermal Stability of PS-PVD YSZ Coatings with Typical Dense Layered and Columnar Structures

by Zefei Cheng, Jiasheng Yang, Fang Shao, Xinghua Zhong, Huayu Zhao, Yin Zhuang, Jing Sheng, Jinxing Ni and Shunyan Tao

Crystals 2020, 10(9), 826; https://doi.org/10.3390/cryst10090826 - 17 Sep 2020

Cited by 10 | Viewed by 3527

Abstract

Yttria-stabilized zirconia (YSZ) coatings with typical pyramid columnar and dense layered structure were prepared by plasma spray-physical vapor deposition (PS-PVD). The evolution behavior of microstructure and crystallography of the coatings before and after thermal aging treatment were observed by electron backscatter diffraction (EBSD) [...] Read more.

Yttria-stabilized zirconia (YSZ) coatings with typical pyramid columnar and dense layered structure were prepared by plasma spray-physical vapor deposition (PS-PVD). The evolution behavior of microstructure and crystallography of the coatings before and after thermal aging treatment were observed by electron backscatter diffraction (EBSD) and field emission scanning electron microscopy (FE-SEM). Results showed that the as-deposited coatings exhibited many types of structures and were mainly composed of a nonequilibrium tetragonal (t’-ZrO₂) phase. With the prolonging of thermal exposure time, the initial nonequilibrium tetragonal phase of YSZ coatings gradually transformed into a monoclinic (m-ZrO₂) phase. During the process of stationary deposition, at a proper spraying distance, each column exhibited a certain preferred orientation, but the ceramic topcoat did not exhibit distinct preferred orientation statistically. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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14 pages, 5679 KiB

Open AccessArticle

Effect of Transition Metals Oxides on the Physical and Mechanical Properties of Sintered Tungsten Heavy Alloys

by Ayman H. Elsayed, Mohamed A. Sayed, Osama M. Dawood and Walid M. Daoush

Crystals 2020, 10(9), 825; https://doi.org/10.3390/cryst10090825 - 17 Sep 2020

Cited by 7 | Viewed by 3113

Abstract

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity [...] Read more.

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity are required for electrical contact applications such as electrical discharge machining (EDM) electrode materials. WHAs were fabricated by compacting its mixed constituents followed by sintering. Ni, Co and Fe are used as binding phases of the tungsten particles and oxides of Zr, Ti and Y are used as oxide dispersing strengthening (ODS) agents of the sintered materials. The results show that all of the chosen factors (i.e., pressure of compaction process, temperature of sintering, type of binding material and type of oxide) have clear effects on all properties of ODS tungsten heavy alloy specimens. The density and electrical conductivity increase with the increase in sintering temperature. Hardness and compression strength were also measured to evaluate the mechanical properties of sintered samples. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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19 pages, 4442 KiB

Open AccessReview

Polymer-Derived Si-Based Ceramics: Recent Developments and Perspectives

by Aidong Xia, Jie Yin, Xiao Chen, Xuejian Liu and Zhengren Huang

Crystals 2020, 10(9), 824; https://doi.org/10.3390/cryst10090824 - 16 Sep 2020

Cited by 32 | Viewed by 5834

Abstract

Polymer derived ceramics (PDCs) are promising candidates for usages as the functionalization of inorganic Si-based materials. Compared with traditional ceramics preparation methods, it is easier to prepare and functionalize ceramics with complex shapes by using the PDCs technique, thereby broadening the application fields [...] Read more.

Polymer derived ceramics (PDCs) are promising candidates for usages as the functionalization of inorganic Si-based materials. Compared with traditional ceramics preparation methods, it is easier to prepare and functionalize ceramics with complex shapes by using the PDCs technique, thereby broadening the application fields of inorganic Si-based ceramics. In this article, we summarized the research progress and the trends of PDCs in recent years, especially most recent three years. Fabrication techniques (traditional preparation, 3D printing, template method, freezing casting techniques, etc.), microstructural tailoring mainly via additive doping, and properties (mechanical, thermal, electrical, as well as dielectric and electromagnetic wave absorption properties) of Si-based PDCs were explicated. Meanwhile, challenges and perspectives for PDCs techniques were proposed as well, with the purpose to enlighten multiple functionalized applications of polymer-derived Si-based ceramics. Full article

(This article belongs to the Special Issue Functionalization of Inorganic Silica-Based Materials)

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10 pages, 3141 KiB

Open AccessArticle

Hardness, Young’s Modulus and Elastic Recovery in Magnetron Sputtered Amorphous AlMgB₁₄ Films

by Alexander M. Grishin

Crystals 2020, 10(9), 823; https://doi.org/10.3390/cryst10090823 - 16 Sep 2020

Cited by 13 | Viewed by 5466

Abstract

We report optical and mechanical properties of hard aluminum magnesium boride films magnetron sputtered from a stoichiometric AlMgB₁₄ ceramic target onto Corning^® 1737 Glass and Si (100) wafers. High target sputtering rf-power and sufficiently short target-to-substrate distance appeared to be critical [...] Read more.

We report optical and mechanical properties of hard aluminum magnesium boride films magnetron sputtered from a stoichiometric AlMgB₁₄ ceramic target onto Corning^® 1737 Glass and Si (100) wafers. High target sputtering rf-power and sufficiently short target-to-substrate distance appeared to be critical processing conditions. Amorphous AlMgB₁₄ films demonstrate very strong indentation size effect (ISE): exceptionally high nanohardness H = 88 GPa and elastic Young’s modulus

E^{*}

= 517 GPa at 26 nm of the diamond probe penetration depth and almost constant values, respectively, of about 35 GPa and 275 GPa starting at depths of about 2–3% of films’ thickness. For comparative analysis of elastic strain to failure index

H / E^{*}

, resistance to plastic deformation ratio

H^{3} / E^{* 2}

and elastic recovery ratio

W_{e}

were obtained in nanoindentation tests performed in a wide range of loading forces from 0.5 to 40 mN. High authentic numerical values of H = 50 GPa and

E^{*}

= 340 GPa correlate with as low as only 10% of total energy dissipating through the plastic deformations. Full article

(This article belongs to the Special Issue Hardmetal)

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18 pages, 1285 KiB

Open AccessArticle

Statistical Crystal Plasticity Model Advanced for Grain Boundary Sliding Description

by Alexey Shveykin, Peter Trusov and Elvira Sharifullina

Crystals 2020, 10(9), 822; https://doi.org/10.3390/cryst10090822 - 16 Sep 2020

Cited by 17 | Viewed by 4028

Abstract

Grain boundary sliding is an important deformation mechanism, and therefore its description is essential for modeling different technological processes of thermomechanical treatment, in particular the superplasticity forming of metallic materials. For this purpose, we have developed a three-level statistical crystal plasticity constitutive model [...] Read more.

Grain boundary sliding is an important deformation mechanism, and therefore its description is essential for modeling different technological processes of thermomechanical treatment, in particular the superplasticity forming of metallic materials. For this purpose, we have developed a three-level statistical crystal plasticity constitutive model of polycrystalline metals and alloys, which takes into account intragranular dislocation sliding, crystallite lattice rotation and grain boundary sliding. A key advantage of our model over the classical Taylor-type models is that it also includes a consideration of grain boundaries and possible changes in their mutual arrangement. The constitutive relations are defined in rate form and in current configuration, which makes it possible to use additive contributions of intragranular sliding and grain boundary sliding to the strain rate at the macrolevel. In describing grain boundary sliding, displacements along the grain boundaries are considered explicitly, and changes in the neighboring grains are taken into account. In addition, the transition from displacements to deformation (shear) characteristics is done for the macrolevel representative volume via averaging, and the grain boundary sliding submodel is attributed to a separate structural level. We have also analyzed the interaction between grain boundary sliding and intragranular inelastic deformation. The influx of intragranular dislocations into the boundary increases the number of defects in it and the boundary energy, and promotes grain boundary sliding. The constitutive equation for grain boundary sliding describes boundary smoothing caused by diffusion effects. The results of the numerical experiments are in good agreement with the known experimental data. The numerical simulation demonstrates that analysis of grain boundary sliding has a significant impact on the results, and the multilevel constitutive model proposed in this study can be used to describe different inelastic deformation regimes, including superplasticity and transitions between conventional plasticity and superplasticity. Full article

(This article belongs to the Special Issue Crystal Plasticity)

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