Crystals

27 pages, 3870 KiB

Open AccessReview

Development of Thermoelectric Half-Heusler Alloys over the Past 25 Years

by Gerda Rogl and Peter Franz Rogl

Crystals 2023, 13(7), 1152; https://doi.org/10.3390/cryst13071152 - 24 Jul 2023

Cited by 22 | Viewed by 4327

Half-Heusler alloys are among the most promising thermoelectric materials. In the present review, thermoelectric properties (at 300 K and 800 K) of more than 1100 compositions from more than 220 publications between 1998 and 2023 were collected and evaluated. The dependence of the [...] Read more.

Half-Heusler alloys are among the most promising thermoelectric materials. In the present review, thermoelectric properties (at 300 K and 800 K) of more than 1100 compositions from more than 220 publications between 1998 and 2023 were collected and evaluated. The dependence of the peak figure of merit, ZT_max, of p- and n-type half-Heusler alloys on the publishing year and the peak temperature is displayed in several figures. Furthermore, plots of ZT vs. the electrical resistivity, the Seebeck coefficient and the thermal conductivity at 300 K and 800 K are shown and discussed. Especially thermal conductivity vs. power factor leads to a good overview of ZT. For both p- and n-type individually separated into systems, ZTs and peak ZTs in dependence on the composition are displayed and discussed. This overview can help to find the ideal half-Heusler alloy for practical use. Full article

(This article belongs to the Special Issue Advances in Thermoelectric Materials 2023-2024)

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17 pages, 14856 KiB

Open AccessArticle

Simulations and Experiments on the Microstructure and Property Evolution of In Situ TiC+Al₃Ti-Reinforced Aluminum Coatings on AZ91D Magnesium Alloy

by Liuqing Yang, Zhiyong Li, Boqiong Li, Yingqiao Zhang, Shouzheng Wei and Yanlong Jia

Crystals 2023, 13(7), 1151; https://doi.org/10.3390/cryst13071151 - 24 Jul 2023

Cited by 4 | Viewed by 1290

Abstract

With the development of computational thermodynamics, it is possible to design a material based on its simulated microstructure and properties before practical operations. In order to improve the surface properties of AZ91D magnesium alloy, Jmatpro was used in this study to design an [...] Read more.

With the development of computational thermodynamics, it is possible to design a material based on its simulated microstructure and properties before practical operations. In order to improve the surface properties of AZ91D magnesium alloy, Jmatpro was used in this study to design an alloy system with in situ TiC+AlTi_3-reinforced aluminum coatings. The Gibbs free energy, hardness, and phase diagrams of aluminum coatings with different ratios of Ti to B₄C were simulated. According to the simulation results, TiB₂, TiC, Al₃Ti_DO₂₂, and Al₄C₃ were formed in the coating while TiB₂, TiC, Al₃Ti_DO₂₂, Al₄C₃, and Al₃Mg₂ were formed in the transition zone between the base metal and the coating. Based on the simulation results, different amounts of Ti were used with B₄C (the ratios were 3:1, 4:1, 5:1, and 6:1) to fabricate TiC+Al₃Ti reinforced aluminum coatings on AZ91D magnesium alloy via laser cladding. The microstructure and phase composition of the coating were studied using scanning electron microscopy (SEM) incorporated with energy- dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results indicated that intermetallic phases, such as AlTi₃(C, N)_0.6, AlMg, Al₃Mg₂, Al₃Ti, and TiC were formed in the coatings. As the Ti content increased, the content of Al₃Ti increased and the content of TiC decreased in the coatings, which is consistent with the simulation results. The average hardness of the coatings was approximately four to five times that of the magnesium alloy substrate, and the corrosion current density of the coatings was around 2.5 × 10⁻⁶, which is two orders of magnitude lower than that of AZ91D magnesium alloy. Full article

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19 pages, 8363 KiB

Open AccessFeature PaperArticle

Research on Single Crystal Preparation via Dynamic Liquid Phase Method

by Xu Wang and Yongmin Zhou

Crystals 2023, 13(7), 1150; https://doi.org/10.3390/cryst13071150 - 24 Jul 2023

Cited by 12 | Viewed by 2187

Abstract

Traditional liquid phase methods for growing single crystals are static growth methods, which include seed crystal sedimentation growth and seed crystal clamping growth using seed crystal holders. Single crystals grown via seed crystal sedimentation often have a flat and elongated shape, and the [...] Read more.

Traditional liquid phase methods for growing single crystals are static growth methods, which include seed crystal sedimentation growth and seed crystal clamping growth using seed crystal holders. Single crystals grown via seed crystal sedimentation often have a flat and elongated shape, and the region in contact with the bottom of the container is restricted during growth, resulting in significant defects. Similarly, the seed crystal clamping growth method cannot avoid contact with external objects, leading to abnormal growth at the contact points and along the direction of the seed crystal holder, also resulting in certain defects. Both of these growth methods require processes, such as cutting and grinding, to remove defects, resulting in resource waste. To address the shortcomings of the static liquid phase single-crystal preparation mentioned above, this study successfully designed a dynamic liquid phase method for single crystal growth, which achieved the successful suspension of seed crystals in the mother solution and the growth of high-quality, large-sized single crystals, avoiding contact with the walls and the bottom of the container during the crystal growth process. Based on the dynamic liquid phase single crystal growth apparatus mentioned above, stable and dynamic liquid phase preparation was successfully achieved, ranging from seed crystals with a diameter of approximately 5 mm to single crystals with a diameter of approximately 20 mm, by controlling the cooling rate and adjusting the solution flow rate. Full article

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23 pages, 6103 KiB

Open AccessReview

Morphological Investigation of Protein Crystals by Atomic Force Microscopy

by Silvia Maria Cristina Rotondi, Giorgia Ailuno, Simone Luca Mattioli, Alessandra Pesce, Ornella Cavalleri and Paolo Canepa

Crystals 2023, 13(7), 1149; https://doi.org/10.3390/cryst13071149 - 24 Jul 2023

Cited by 2 | Viewed by 2577

Abstract

In this review, we discuss the progress in the investigation of macromolecular crystals obtained through the use of atomic force microscopy (AFM), a powerful tool for imaging surfaces and specimens at high resolution. AFM enables the visualization of soft samples at the nanoscale [...] Read more.

In this review, we discuss the progress in the investigation of macromolecular crystals obtained through the use of atomic force microscopy (AFM), a powerful tool for imaging surfaces and specimens at high resolution. AFM enables the visualization of soft samples at the nanoscale and can provide precise visual details over a wide size range, from the molecular level up to hundreds of micrometers. The nonperturbative nature, the ability to scan in a liquid environment, and the lack of need for freezing, fixing, or staining make AFM a well-suited tool for studying fragile samples such as macromolecular crystals. Starting from the first morphological investigations revealing the surface morphology of protein crystals, this review discusses the achievements of AFM in understanding the crystal growth processes, both at the micro- and nanoscale. The capability of AFM to investigate the sample structure at the single molecular level is analyzed considering in-depth the structure of S-layers. Lastly, high-speed atomic force microscopy (HS-AFM) is discussed as the evolution to overcome the limitations of low imaging speed, allowing for the observation of molecular dynamics and weakly adsorbed, diffusing molecules. HS-AFM has provided intuitive views and directly visualized phenomena that were previously described indirectly, answering questions that were challenging to address using other characterization methods. Full article

(This article belongs to the Special Issue Membrane Protein Crystallography)

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20 pages, 5015 KiB

Open AccessArticle

Preparation and Characterization of Nano-Sized Co(II), Cu(II), Mn(II) and Ni(II) Coordination PAA/Alginate Biopolymers and Study of Their Biological and Anticancer Performance

by Maged S. Al-Fakeh, Munirah S. Alazmi and Yassine EL-Ghoul

Crystals 2023, 13(7), 1148; https://doi.org/10.3390/cryst13071148 - 23 Jul 2023

Cited by 4 | Viewed by 1959

Abstract

Four of the crosslinked sodium alginate and polyacrylic acid biopolymers based nanoscale metal natural polysaccharides, [M(AG-PAA)Cl(H₂O)₃], where M = Co(II), Cu(II), Mn(II) and Ni(II), AG = sodium alginate and PAA = polyacrylic acid, have been synthesized and structurally characterized. [...] Read more.

Four of the crosslinked sodium alginate and polyacrylic acid biopolymers based nanoscale metal natural polysaccharides, [M(AG-PAA)Cl(H₂O)₃], where M = Co(II), Cu(II), Mn(II) and Ni(II), AG = sodium alginate and PAA = polyacrylic acid, have been synthesized and structurally characterized. Because of their numerous biological and pharmacological activities of polysaccharides, including antimicrobial, immunomodulatory, antitumor, antidiabetic, antiviral, antioxidant, hypoglycemic and anticoagulant activities, polysaccharides are one of the near-promising candidates in the biomedical and pharmaceutical fields. The complexity of the polymeric compounds has been verified by carbon and nitrogen analysis, magnetic and conductance measurements, FT-IR spectra, electronic spectral analysis and thermal analysis (DTA, TG). All the synthesized complexes were non-electrolytes with magnetic moments ranging from 1.74 to 5.94 BM. The polymeric complexes were found to be of octahedral geometry. The developed coordination polymeric was found to be crystalline using X-ray powder diffraction examinations, which is confirmed by the SEM analysis. As a result, the crystallite size of all polymeric nanocrystals was in the range of 14 - 69 nm. The test of four compounds exhibits a broad spectrum of antimicrobial activity against both Gram-positive and Gram-negative bacteria and fungal Candida albicans. Using DPPH as a substrate, studies on radical scavenging tests are carried out. The findings demonstrated the antioxidant activities of each complex. In addition, results showed that the two chosen polymeric complexes had a good ability to kill cancer cells in a dose-dependent way. The copper(II) polymeric complex showed to its superior functionality as evidenced by microbial activity. After 72 h of interaction with the normal human breast epithelial cells (MCF10A), the synthesized polymeric compounds of Cu(II) and Co(II) showed exceptional cytocompatibility with the different applied doses. Compared to poly-AG/PAA/Co(II), poly-AG/PAA/Cu(II) exhibits a greater anticancer potential at various polymeric dosages. Full article

(This article belongs to the Special Issue Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Crystalline Materials)

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18 pages, 7921 KiB

Open AccessArticle

Negative Linear Compressibility of Formate Crystals from the Viewpoint of Quantum Electronic Pressure

by Yury V. Matveychuk, Sergey A. Sobalev, Polina I. Borisova, Ekaterina V. Bartashevich and Vladimir G. Tsirelson

Crystals 2023, 13(7), 1147; https://doi.org/10.3390/cryst13071147 - 23 Jul 2023

Cited by 1 | Viewed by 1408

Abstract

In order to understand the phenomenon of negative linear compressibility (NLC) in organic crystals, it is necessary to investigate not only the structural features but also the electronic changes taking place under external hydrostatic pressure. It is also necessary to clarify which electronic [...] Read more.

In order to understand the phenomenon of negative linear compressibility (NLC) in organic crystals, it is necessary to investigate not only the structural features but also the electronic changes taking place under external hydrostatic pressure. It is also necessary to clarify which electronic properties allow the quantification and comparison of the compressibility of crystals. In our study, the crystal structures of sodium and cadmium formates under hydrostatic compression were modeled, as well as the α and β-phases of calcium formate. The changes in cell parameters and spatial dependences of the linear compressibility were analyzed, and the ranges of external pressure, which must be applied for NLC onset, were predicted for the sodium and α-calcium formates. Although the behavior of chemical bonds is not predicted by the sign or absolute value of the quantum electronic pressure, its relative change under external pressure clearly distinguishes the soft and rigid regions in a crystal. The relationship between the NLC values and the changes in quantum electronic pressure in the cavities of formate crystals was established. Full article

(This article belongs to the Topic Mathematical Applications of Nonlinear Wave Properties in Crystalline and Dispersive Media)

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20 pages, 4469 KiB

Open AccessArticle

High-Cycle Fatigue Behavior of D2 Wheel Steel under Uniaxial and Multiaxial Loading Conditions for Potential Applications in the Railway Industry

by Shan Li and Yongxiang Zhao

Crystals 2023, 13(7), 1146; https://doi.org/10.3390/cryst13071146 - 22 Jul 2023

Viewed by 1737

Abstract

This study investigates the fatigue damage evolution mechanisms of D2 wheel steel under high-cycle uniaxial and multiaxial loading conditions, with a focus on determining the fatigue crack growth threshold (FCGT). Uniaxial and multiaxial FCGT tests were performed on pre-cracked D2 wheel steel specimens [...] Read more.

This study investigates the fatigue damage evolution mechanisms of D2 wheel steel under high-cycle uniaxial and multiaxial loading conditions, with a focus on determining the fatigue crack growth threshold (FCGT). Uniaxial and multiaxial FCGT tests were performed on pre-cracked D2 wheel steel specimens subjected to high-frequency cyclic loading at stress ratios (R) of 0.1. The results indicate that the FCGT for D2 wheel steel under uniaxial loading conditions ranges between 8–9 MPa.m^0.5, while under multiaxial loading conditions, it ranges between 6–9 MPa.m^0.5. Scanning electron microscopy analysis revealed differences in the crack propagation mechanisms between the uniaxial and multiaxial tests, with cracks deviating from their path and following the microstructure in the uniaxial tests, and cracks propagating along planes of weakness in the multiaxial tests. These findings provide insights into the high-cycle fatigue behavior of D2 wheel steel under different loading conditions for potential applications in the railway industry. Full article

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11 pages, 3234 KiB

Open AccessArticle

Effects of Buffer Layer on Structural Properties of Nonpolar (11

\bar{2}

0)-Plane GaN Film

by Jianguo Zhao, Boyan Suo, Ru Xu, Tao Tao, Zhe Zhuang, Bin Liu, Xiong Zhang and Jianhua Chang

Crystals 2023, 13(7), 1145; https://doi.org/10.3390/cryst13071145 - 22 Jul 2023

Cited by 2 | Viewed by 1498

Abstract

Nonpolar (11

\bar{2}

0) a-plane GaN films were grown on semipolar (1

\bar{1}

02) r-plane sapphire substrates using various buffer layers within a low-pressure metal organic chemical vapor deposition system. The structural properties of nonpolar a-plane GaN films [...] Read more.

Nonpolar (11

\bar{2}

0) a-plane GaN films were grown on semipolar (1

\bar{1}

02) r-plane sapphire substrates using various buffer layers within a low-pressure metal organic chemical vapor deposition system. The structural properties of nonpolar a-plane GaN films were intensively investigated by X-ray diffraction and Raman spectra measurements. A set of buffer layers were adopted from a GaN layer to a composite layer containing a multiple AlN layers and a gradually varied-Al-content AlGaN layer, the full width at half maximum of the X-ray rocking curves measured along the [0001] and [10

\bar{1}

0] directions of a-plane GaN were reduced by 35% and 37%, respectively. It was also found that the basal-plane stacking faults (BSFs) density can be effectively reduced by the heterogeneous interface introduced together with the composite buffer layer. An order of magnitude reduction in BSFs density, as low as 2.95 × 10⁴ cm⁻¹, and a pit-free surface morphology were achieved for the a-plane GaN film grown with the composite buffer layer, which is promising for the development of nonpolar GaN-based devices in the future. Full article

(This article belongs to the Special Issue Epitaxial Growth of Crystalline Semiconductors)

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20 pages, 4586 KiB

Open AccessReview

Multifunctional Polymeric Nanocomposites for Sensing Applications—Design, Features, and Technical Advancements

by Ayesha Kausar, Ishaq Ahmad, Tingkai Zhao, Osamah Aldaghri, Khalid H. Ibnaouf and M. H. Eisa

Crystals 2023, 13(7), 1144; https://doi.org/10.3390/cryst13071144 - 22 Jul 2023

Cited by 8 | Viewed by 3119

Abstract

Among nanocomposite materials, multifunctional polymer nanocomposites have prompted important innovations in the field of sensing technology. Polymer-based nanocomposites have been successfully utilized to design high-tech sensors. Thus, conductive, thermoplast, or elastomeric, as well as natural polymers have been applied. Carbon nanoparticles as well [...] Read more.

Among nanocomposite materials, multifunctional polymer nanocomposites have prompted important innovations in the field of sensing technology. Polymer-based nanocomposites have been successfully utilized to design high-tech sensors. Thus, conductive, thermoplast, or elastomeric, as well as natural polymers have been applied. Carbon nanoparticles as well as inorganic nanoparticles, such as metal nanoparticles or metal oxides, have reinforced polymer matrices for sensor fabrication. The sensing features and performances rely on the interactions between the nanocomposites and analytes like gases, ions, chemicals, biological species, and others. The multifunctional nanocomposite-derived sensors possess superior durability, electrical conductivity, sensitivity, selectivity, and responsiveness, compared with neat polymers and other nanomaterials. Due to the importance of polymeric nanocomposite for sensors, this novel overview has been expanded, focusing on nanocomposites based on conductive/non-conductive polymers filled with the nanocarbon/inorganic nanofillers. To the best of our knowledge, this article is innovative in its framework and the literature covered regarding the design, features, physical properties, and the sensing potential of multifunctional nanomaterials. Explicitly, the nanocomposites have been assessed for their strain-sensing, gas-sensing, bio-sensing, and chemical-sensing applications. Here, analyte recognition by nanocomposite sensors have been found to rely on factors such as nanocomposite design, polymer type, nanofiller type, nanofiller content, matrix–nanofiller interactions, interface effects, and processing method used. In addition, the interactions between a nanocomposite and analyte molecules are defined by high sensitivity, selectivity, and response time, as well as the sensing mechanism of the sensors. All these factors have led to the high-tech sensing applications of advanced nanocomposite-based sensors. In the future, comprehensive attempts regarding the innovative design, sensing mechanism, and the performance of progressive multifunctional nanocomposites may lead to better the strain-sensing, gas/ion-sensing, and chemical-sensing of analyte species for technical purposes. Full article

(This article belongs to the Special Issue Advances in Multifunctional Nanocomposites)

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21 pages, 13340 KiB

Open AccessReview

Combustion Synthesis of MAX Phases: Microstructure and Properties Inherited from the Processing Pathway

by Sofiya Aydinyan

Crystals 2023, 13(7), 1143; https://doi.org/10.3390/cryst13071143 - 22 Jul 2023

Cited by 3 | Viewed by 1961

Abstract

The MAX phases exhibit outstanding combination of strength and ductility which are unique features of both metals and ceramics. The preparation of pure MAX phases has been challenging due to the thermodynamic auspiciousness of intermetallic formation in the ternary systems. This review demonstrates [...] Read more.

The MAX phases exhibit outstanding combination of strength and ductility which are unique features of both metals and ceramics. The preparation of pure MAX phases has been challenging due to the thermodynamic auspiciousness of intermetallic formation in the ternary systems. This review demonstrates the power of the self-propagating, high-temperature synthesis method, delivers the main findings of the combustion synthesis optimization of the MAX phases, and reveals the influence of the combustion wave on the microstructure features thereof. The possibility of using elements and binary compounds as precursors, oxidizers, and diluents to control the exothermicity was comparatively analyzed from the point of view of the final composition and microstructure in the following systems: Ti-Al-C, Ti-V-Al-C, Cr-V-Al-C, Ti-Cr-Al-C, Ti-Nb-Al-C, Ti-Al-Si-C, Ti-Al-Sn-C, Ti-Al-N, Ti-Al-C-N, Ti-Al-B, Ti-Si-B, Ti-Si-C, Nb-Al-C, Cr-Al-C, Cr-Mn-Al-C, V-Al-C, Cr-V-Al-C, Ta-Al-C, Zr-S-C, Cr-Ga-C, Zr-Al-C, and Mo-Al-C, respectively. The influence of sample preparation (including the processes of preheating, mechanical activation, and microwave heating, sample geometry, porosity, and cold pressing) accompanied with the heating and cooling rates and the ambient gas pressure on the combustion parameters was deduced. The combustion preparation of the MAX phases was then summarized in chronological order. Further improvements of the synthesis conditions, along with recommendations for the products quality and microstructure control were given. The comparison of the mechanical properties of the MAX phases prepared by different approaches was illustrated wherever relevant. Full article

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14 pages, 1759 KiB

Open AccessArticle

Excitation Density Effects in the Luminescence Yield and Kinetics of MAPbBr₃ Single Crystals

by Andrey N. Belsky, Nikita A. Fedorov, Ivan A. Frolov, Irina A. Kamenskikh, Patrick Martin, Elizaveta D. Rubtsova, Igor N. Shpinkov, Dmitry A. Spassky, Andrey N. Vasil’ev and Boris I. Zadneprovsky

Crystals 2023, 13(7), 1142; https://doi.org/10.3390/cryst13071142 - 22 Jul 2023

Viewed by 1425

Abstract

The luminescent Z-scan technique with time resolution is applied to the study of the luminescence properties of CH₃NH₃PbBr₃ single crystals representative of the family of hybrid organic–inorganic lead perovskites successfully applied recently in photovoltaics and currently investigated as [...] Read more.

The luminescent Z-scan technique with time resolution is applied to the study of the luminescence properties of CH₃NH₃PbBr₃ single crystals representative of the family of hybrid organic–inorganic lead perovskites successfully applied recently in photovoltaics and currently investigated as potential nanosecond scintillators. The third harmonic of Ti-sapphire laser (λ = 266 nm) with a pulse duration of 26 fs and 1 kHz frequency was applied for the luminescence excitation creating the charge carriers with the estimated density from 10¹⁷ to 10²¹ cm⁻³ in the temperature range from 13 to 300 K. Temperature and excitation density dependence of the luminescence yield and kinetics is interpreted with the consideration of the temperature-dependent binding of electrons and holes into excitons, a saturation of defects responsible for the non-radiative relaxation channel competing with exciton creation; absorption saturation resulting in the increased penetration depth of the excitation radiation and hence the increased contribution of the re-absorption. Full article

(This article belongs to the Special Issue Advances in Crystals for Optoelectronics)

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10 pages, 1604 KiB

Open AccessArticle

Combining UV-Vis and Resonance Raman Spectroscopy to Characterize Molecular Aggregation

by Valentina Sesti, Micol D’Antonio, Andrea Lucotti, Paola Moretti, Rossella Castagna, Chiara Bertarelli and Matteo Tommasini

Crystals 2023, 13(7), 1141; https://doi.org/10.3390/cryst13071141 - 22 Jul 2023

Cited by 1 | Viewed by 1975

Abstract

In this work, we use UV-Vis and Raman spectroscopy to correlate the intensity of selected transitions to the onset of aggregation phenomena. Through TDDFT calculations, we rationalize the formation of H-aggregates and their influence on the observed changes in the UV-Vis spectra. A [...] Read more.

In this work, we use UV-Vis and Raman spectroscopy to correlate the intensity of selected transitions to the onset of aggregation phenomena. Through TDDFT calculations, we rationalize the formation of H-aggregates and their influence on the observed changes in the UV-Vis spectra. A correlation between Raman intensity and the molar absorption coefficient is experimentally observed and theoretically rationalized. We develop this method by considering Disperse Orange 3 (DO3), a well-known push–pull azobenzene dye with strong optical absorption in the blue–green region of the visible spectrum, and the known tendency to form H-aggregates. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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12 pages, 2976 KiB

Open AccessArticle

Cold Sintering Isomagnetic Dielectric NaCl-Nickel Zinc Ferrite Composite Ceramics

by Jiuyuan Han, Mengjiao Chi, Liu Yang, Bing Liu, Minmin Mao, Hadi Barzegar Bafrooei, Zhongyan Ma, Yingjie Ren, Feng Shi, Ehsan Taheri-Nassaj, Dawei Wang and Kaixin Song

Crystals 2023, 13(7), 1140; https://doi.org/10.3390/cryst13071140 - 21 Jul 2023

Cited by 3 | Viewed by 1924

Abstract

In this study, dense composites of xNaCl-(1−x)Ni_0.5Zn_0.5Fe₂O₄ (referred to as NaCl-NZO) and xH₃BO₃-(0.8−x)Ni_0.5Zn_0.5Fe₂O₄-0.2NaCl (referred to as HB-NZO-NaCl) were prepared using the cold sintering process. [...] Read more.

In this study, dense composites of xNaCl-(1−x)Ni_0.5Zn_0.5Fe₂O₄ (referred to as NaCl-NZO) and xH₃BO₃-(0.8−x)Ni_0.5Zn_0.5Fe₂O₄-0.2NaCl (referred to as HB-NZO-NaCl) were prepared using the cold sintering process. The objective was to investigate the cold sintering procedure for fabricating ferrite composite ceramics with comparable permeability and dielectric constants suitable for radio-frequency electronic device applications. Optimal cold sintering conditions were determined as 200 °C/30 min/500 MPa with a relative density of 95% for NaCl-NZO and 120 °C/30 min/300 MPa with a relative density of 95.4% for HB-NZO-NaCl. X-ray diffraction and scanning electron microscope analyses confirmed the absence of secondary phases. The resulting composite ceramics showed promising characteristics, with the 0.5NaCl-0.5NZO composition exhibiting a dielectric constant of 6.2 @ 100 MHz, dielectric loss of 0.02 @ 100 MHz, permeability of 2.5 @ 100 MHz, and magnetic loss of 0.001 @ 100 MHz. Similarly, the 0.3HB-0.5NZO-0.2NaCl composition displayed a dielectric constant of 5.9 @ 100 MHz, dielectric loss of 0.02 @ 100 MHz, permeability of 5.1 @ 100 MHz, and magnetic loss of 5 × 10⁻⁴ @ 100 MHz. These findings indicate potential applications in wireless communication. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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27 pages, 3455 KiB

Open AccessReview

Next-Generation Quantum Materials for Thermoelectric Energy Conversion

by Shiva Kumar Singh, Julian Munevar, Letície Mendonça-Ferreira and Marcos A. Avila

Crystals 2023, 13(7), 1139; https://doi.org/10.3390/cryst13071139 - 21 Jul 2023

Cited by 1 | Viewed by 3637

Abstract

This review presents the recent advances in the search for thermoelectric (TE) materials, mostly among intermetallic compounds and in the enhancement of their TE performance. Herein, contemporary approaches towards improving the efficiency of heat–electricity conversion (e.g., energy harvesting and heat pumping) are discussed [...] Read more.

This review presents the recent advances in the search for thermoelectric (TE) materials, mostly among intermetallic compounds and in the enhancement of their TE performance. Herein, contemporary approaches towards improving the efficiency of heat–electricity conversion (e.g., energy harvesting and heat pumping) are discussed through the understanding of various emergent physical mechanisms. The strategies for decoupling the individual TE parameters, as well as the simultaneous enhancement of the TE power factor and the suppression of heat conduction, are described for nanoparticle-doped materials, high entropy alloys, and nanowires. The achievement of a superior TE performance due to emergent quantum phenomena is discussed for intermetallic chalcogenides and related systems (e.g., strong and weak topological insulators, Weyl and Dirac semimetals), and some of the most promising compounds within these classes are highlighted. It was concluded that high-entropy alloying provides a methodological breakthrough for employing band engineering methods along with various phonon scattering mechanisms towards significant TE efficiency improvement in conventional TE materials. Finally, topological semimetals and magnetic semimetals with several intriguing features, such as a violation of the Wiedemann–Franz law and outstanding perpendicular Nernst signals, are presented as strong candidates for becoming next-generation TE quantum materials. Full article

(This article belongs to the Special Issue Advances in Intermetallic and Metal-Like Compounds)

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20 pages, 8064 KiB

Open AccessArticle

Effect of Microchemistry Elements in Relation of Laser Welding Parameters on the Morphology 304 Stainless Steel Welds Using Response Surface Methodology

by Kamel Touileb, Elawady Attia, Rachid Djoudjou, Abdejlil Chihaoui Hedhibi, Abdallah Benselama, Albaijan Ibrahim and Mohamed M. Z. Ahmed

Crystals 2023, 13(7), 1138; https://doi.org/10.3390/cryst13071138 - 21 Jul 2023

Cited by 2 | Viewed by 1324

Abstract

Small differences in the contents of surface active elements can change flow direction and thus heat transfer, even for different batches of a given alloy. This study aims to determine the effects of sulfur on weld bead morphology in the laser process. The [...] Read more.

Small differences in the contents of surface active elements can change flow direction and thus heat transfer, even for different batches of a given alloy. This study aims to determine the effects of sulfur on weld bead morphology in the laser process. The paper presents the results related to the weld bead shape of two thin AISI 304 industrial stainless steel casts. One cast contains 80 ppm (0.008%) of sulfur, considered as a high sulfur content, and the other one contains 30 ppm (0.003%) sulfur, which can be considered low sulfur. The welds were executed using a CO₂ laser. The effects of laser power (3.75, 3.67, 6 kW), welding speed (1.25, 2.40, 2.45, 3.6 m/min), focus point position (2, 7, 12 mm), and shield gas (Helium, mixed 40% helium + 60% argon and mixed 70% helium + 30% argon) with a flow rate of 10 L/min on the depth of the weld (D) and the aspect ratio (R = D/W) were investigated using RSM (response surface methodology). The experimental results show that the transfer of energy from the laser beam to the workpiece can be total in cases where the selected welding parameters prevent plasma formation. For the 304 HS cast, the focus point is the major factor in determining the depth of penetration, and its contribution is up to 52.35%. However, for 304 LS, the interaction between shield gas and focus point seems to play an important role, and the contribution of their interaction raises to 28% in relation to the laser depth of the weld. Moreover, the study shows that sulfur plays a surface-active role only in the case of partial penetration beads, so that a 56% partially penetrated weld supports the hypothesis of its surface-active role in the formation of the weld pool. However, a penetration of only 36% confirms the effects of a sulfur surface-active when the bead is fully penetrated. Full article

(This article belongs to the Special Issue Welding and Joining of Metallic Materials: Microstructure and Mechanical Properties)

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13 pages, 5799 KiB

Open AccessArticle

Anomalous Ferromagnetic Phase in the Gd_1−xEr_xB₄ Series: Crystal Growth, Thermal, and Magnetic Properties

by Sueli H. Masunaga, Vagner B. Barbeta, Fábio Abud, Milton S. Torikachvili and Renato F. Jardim

Crystals 2023, 13(7), 1137; https://doi.org/10.3390/cryst13071137 - 21 Jul 2023

Cited by 1 | Viewed by 1181

Abstract

Rare-earth tetraborides RB₄ are of great interest due to the occurrence of geometric magnetic frustration and corresponding unusual magnetic properties. While the Gd³⁺ spins in GdB₄ align along the ab plane, Er³⁺ spins in the isomorphic ErB₄ [...] Read more.

Rare-earth tetraborides RB₄ are of great interest due to the occurrence of geometric magnetic frustration and corresponding unusual magnetic properties. While the Gd³⁺ spins in GdB₄ align along the ab plane, Er³⁺ spins in the isomorphic ErB₄ are confined to the c–axis. The magnetization in the latter exhibits a plateau at the midpoint of the saturation magnetization. Therefore, solid solutions of (Gd, Er)B₄ provide an excellent playground for exploring the intricate magnetic behavior in these compounds. Single crystals of Gd_1−xEr_xB₄ (x = 0, 0.2, and 0.4) were grown in aluminum flux. X-ray diffraction scans revealed single-phase materials, and a drop in the unit cell volume with increasing Er content, suggesting the partial substitution of Er at the Gd sites. Heat capacity measurements indicated a systematic decrease of the Néel temperature (T_N) with increasing Er content. The effective magnetic moment determined from the magnetization measurement agreed with the calculated free ion values for Gd³⁺ and Er³⁺, providing further evidence for the successful substitution of Er for Gd. The partial substitution resulted in an anomalous ferromagnetic phase below T_N, exhibiting significant anisotropy, predominantly along the c-axis. This intriguing behavior merits further studies of the magnetism in the Gd_1−xEr_xB₄ borides. Full article

(This article belongs to the Special Issue Advances in Intermetallic and Metal-Like Compounds)

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11 pages, 4345 KiB

Open AccessArticle

High-Conductivity MXene Film-Based Millimeter Wave Antenna for 5G Applications

by Jiannan Guo, Yunfa Si, Rongguo Song, Haoran Zu, Yitong Xin, Dong Ye, Ming Xu, Bao-Wen Li and Daping He

Crystals 2023, 13(7), 1136; https://doi.org/10.3390/cryst13071136 - 21 Jul 2023

Cited by 3 | Viewed by 1922

Abstract

Millimeter wave antennas have the advantage of high directivity, miniaturization, high resolution and data transfer speed, wide bandwidth, and lower latency. In this work, a millimeter wave planar array antenna (PAA) with the characteristics of wideband and low sidelobes, which consists of eight [...] Read more.

Millimeter wave antennas have the advantage of high directivity, miniaturization, high resolution and data transfer speed, wide bandwidth, and lower latency. In this work, a millimeter wave planar array antenna (PAA) with the characteristics of wideband and low sidelobes, which consists of eight identical linear array antenna (LAA) based on Ti₃C₂ MXene, is designed and fabricated. It is the first time that MXene antennas are proposed for a 5G millimeter wave antenna application. MXene PAA has a high realized gain of 22.22 dBi and a −10 dB impedance bandwidth of measurement covering the range from 24 GHz to 28 GHz, including the 5G FR2—n258 frequency band. With Chebyshev current distribution, the MXene PAA has a half-power beam width of 10.2° and 10.8° in the xoz-plane and yoz-plane radiation patterns with the sidelobes levels below −20 dB, respectively. Therefore, MXene PAA is suitable for 5G mobile communication applications. Full article

(This article belongs to the Section Materials for Energy Applications)

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9 pages, 2091 KiB

Open AccessArticle

Interaction between the L-Ascorbic Acid and the HO₂ Hydroperoxyl Radical: An Ab Initio Study

by Iván Carrillo Díaz, Ali Fransuani Jiménez González, Juan Manuel Ramírez-de-Arellano and Luis Fernando Magaña

Crystals 2023, 13(7), 1135; https://doi.org/10.3390/cryst13071135 - 20 Jul 2023

Viewed by 1342

Abstract

We studied the interaction between the L-ascorbic acid C₆H₈O₆ and the HO₂ hydroperoxyl radical, using DFT ab initio methods. The purpose of this study is to explore whether the L-ascorbic acid would be able to interact with [...] Read more.

We studied the interaction between the L-ascorbic acid C₆H₈O₆ and the HO₂ hydroperoxyl radical, using DFT ab initio methods. The purpose of this study is to explore whether the L-ascorbic acid would be able to interact with and possibly reduce the hydroperoxyl radical. We performed static calculations consisting of structural optimizations, using the pseudopotential formalism and the LDA, PBE, and BLYP density functional approximations, including van der Waals corrections. For all the cases considered, we found an interaction between C₆H₈O₆ and HO₂, reporting recovery times and absorption energies consistent with a physisorption process and confirming the ability of the L-ascorbic acid to act as a sensor of the HO₂ radical. Full article

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15 pages, 7042 KiB

Open AccessArticle

Development of the Forming Limit Diagram for AA6016-T4 at Room Temperature Using Uniaxial Tension of Notched Samples and a Biaxial Test

by Ahmed Elsayed, Diego Gonzalez and Evgenia Yakushina

Crystals 2023, 13(7), 1134; https://doi.org/10.3390/cryst13071134 - 20 Jul 2023

Viewed by 2027

Abstract

Within the framework of the formability limit assessment in sheet metal forming, testing of notched tensile samples coupled with digital image correlation (DIC) has been analysed as an alternative to overcome the implications of Nakajima testing in relation to times of test preparation, [...] Read more.

Within the framework of the formability limit assessment in sheet metal forming, testing of notched tensile samples coupled with digital image correlation (DIC) has been analysed as an alternative to overcome the implications of Nakajima testing in relation to times of test preparation, cost of the equipment, presence of friction, and amount of material required for the test. Additionally, the complications of the Nakajima testing at elevated temperatures need to also be considered. In this work, specific notched sample geometries have been investigated to accurately identify the forming limits of Aluminium alloy AA6016 in T4 condition. Once the notched geometry had been defined, experimental tensile testing of the samples coupled with DIC technology allowed us to identify the formability limits of interest. Finally, a comparison at room temperature with the conventional Nakajima testing was performed experimentally. Two different methodologies for strain limit evaluation in notched samples have been investigated in the present analysis. The first one is called a position-dependent method and is based on the inverse best-fit parabola of the “bell-shaped curve”, which is used in the conventional Nakajima test. The second approach referred to a time-dependent method and is based on the strain rate evaluation at the necking zone. This strain-rate-dependent method, which works in combination with DIC measurements, was found to be more accurate to determine the necking limits than the previous one; in addition, it also provides more accurate information for the safe zone of forming. Full article

(This article belongs to the Special Issue Crystal Plasticity (Volume III))

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18 pages, 5700 KiB

Open AccessEditor’s ChoiceArticle

Structure, Conformation and Contact Analyses of Six Aromatic Diamide Diesters

by Islam Ali Osman, Vickie McKee, Christian Jelsch and John F. Gallagher

Crystals 2023, 13(7), 1133; https://doi.org/10.3390/cryst13071133 - 20 Jul 2023

Cited by 1 | Viewed by 1461

Abstract

Six meta-substituted isophthalamide diesters (DxE) and pyridinedicarboxamides (PxE) are reported with spectroscopic and crystal structure analyses (D = meta-C₆H₄; P = meta-pyridine; xE = 2-/3-/4-ethyl ester substitution). Comparisons are made between [...] Read more.

Six meta-substituted isophthalamide diesters (DxE) and pyridinedicarboxamides (PxE) are reported with spectroscopic and crystal structure analyses (D = meta-C₆H₄; P = meta-pyridine; xE = 2-/3-/4-ethyl ester substitution). Comparisons are made between the solid-state and minimised structures from ab initio computational calculations. The six compounds are potentially useful ligands for metal-complex coordination, spanning a range of molecular conformations. D2E adopts a planar molecular structure, as influenced by the C-H⋯O intramolecular interactions with all 34 nonhydrogen atoms within 0.1 Å of the D2E mean molecular plane. Extensive intermolecular ring⋯ring stacking arises with the shortest interplanar C⋯C of 3.372(2) Å. For D3E (Z′ = 4) and D4E, the hierarchy of intermolecular interactions is the determining factor driving the crystal structure formation with concomitant twinning, as influenced by the weaker interactions. In the pyridine-related P2E, the O1W water molecule (site occupancy = 0.441(5)) forms four hydrogen bonds, as follows: (i) O1W−H⋯O=C, (ii) O1W−H⋯π(arene) and (iii) two _aromaticC−H⋯O1W. The meta- and para-substituted PxE·2(H₂O) structures (x = 3 or 4) adopt open conformations with pairs of hydrogen-bonded water molecules located in molecular niches between the flanking benzamide ester groups. The Hirshfeld surface, two-dimensional fingerprint plots and contact enrichment ratio were investigated to statistically analyse the different types of intermolecular interactions. Full article

(This article belongs to the Section Organic Crystalline Materials)

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14 pages, 4212 KiB

Open AccessArticle

Study on Efficient Dephosphorization in Converter Based on Thermodynamic Calculation

by Zhong-Liang Wang, Tian-Le Song, Li-Hua Zhao and Yan-Ping Bao

Crystals 2023, 13(7), 1132; https://doi.org/10.3390/cryst13071132 - 20 Jul 2023

Cited by 1 | Viewed by 1499

Abstract

Given the accelerating depletion of iron ore resources, there is growing concern within the steel industry regarding the availability of high-phosphorus iron ore. However, it is important to note that the utilization of high-phosphorus iron ore may result in elevated phosphorus content and [...] Read more.

Given the accelerating depletion of iron ore resources, there is growing concern within the steel industry regarding the availability of high-phosphorus iron ore. However, it is important to note that the utilization of high-phosphorus iron ore may result in elevated phosphorus content and notable fluctuations in molten iron, thereby imposing additional challenges on the dephosphorization process in steelmaking. The most urgent issue in the process of converter steelmaking is how to achieve efficient dephosphorization. In this study, the influence of various factors on the logarithm of the phosphorus balance distribution ratio (

\lg L_{p}

), the logarithm of the P₂O₅ activity coefficient (

\lg γ_{P_{2} O_{5}}

), and the logarithm of the phosphorus capacity (

\lg C_{p}

) were examined through thermodynamic calculations. The impact of each factor on dephosphorization was analyzed, and the optimal conditions for the dephosphorization stage of the converter were determined. Furthermore, the influence of basicity and Fe_tO content on the form of phosphorus in the slag was analyzed using FactSage 7.2 software, and the precipitation rules of the slag phases were explored. The thermodynamic calculation results indicated that increasing the basicity of the dephosphorization slag was beneficial for dephosphorization, but it should be maintained below 3. The best dephosphorization effect was achieved when the Fe_tO content was around 20%. The reaction temperature during the dephosphorization stage should be kept low, as the dephosphorization efficiency decreased sharply with the increasing temperature. In dephosphorization slag, Ca₃(PO₄)₂ usually formed a solid solution with Ca₂SiO₄, so the form of phosphorus in the slag was mainly determined by the precipitation form and content of Ca₂SiO₄. The phases in the dephosphorization slag mainly consisted of a phosphorus-rich phase, an iron-rich phase, and a matrix phase. The results of scanning electron microscopy and X-ray diffraction analyses were consistent with the thermodynamic calculation results. Full article

(This article belongs to the Special Issue Advanced Crystalline Materials, Mechanical Properties and Innovative Production Systems)

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13 pages, 2082 KiB

Open AccessArticle

Large-Scale Production and Optical Properties of a High-Quality SnS₂ Single Crystal Grown Using the Chemical Vapor Transportation Method

by Prashant Tripathi, Arun Kumar, Prashant K. Bankar, Kedar Singh and Bipin Kumar Gupta

Crystals 2023, 13(7), 1131; https://doi.org/10.3390/cryst13071131 - 20 Jul 2023

Cited by 3 | Viewed by 1751

Abstract

The scientific community believes that high-quality, bulk layered, semiconducting single crystals are crucial for producing two-dimensional (2D) nanosheets. This has a significant impact on current cutting-edge science in the development of next-generation electrical and optoelectronic devices. To meet this ever-increasing demand, efforts have [...] Read more.

The scientific community believes that high-quality, bulk layered, semiconducting single crystals are crucial for producing two-dimensional (2D) nanosheets. This has a significant impact on current cutting-edge science in the development of next-generation electrical and optoelectronic devices. To meet this ever-increasing demand, efforts have been made to manufacture high-quality SnS₂ single crystals utilizing low-cost CVT (chemical vapor transportation) technology, which allows for large-scale crystal production. Based on the chemical reaction that occurs throughout the CVT process, a viable mechanism for SnS₂ growth is postulated in this paper. Optical, XRD with Le Bail fitting, TEM, and SEM are used to validate the quality, phase, gross structural/microstructural analyses, and morphology of SnS₂ single crystals. Furthermore, Raman, TXRF, XPS, UV–Vis, and PL spectroscopy are used to corroborate the quality of the SnS₂ single crystals, as well as the proposed energy level diagram for indirect transition in the bulk SnS₂ single crystals. As a result, the suggested method provides a cost-effective method for growing high-quality SnS₂ single crystals, which could lead to a new alternative resource for producing 2D SnS₂ nanosheets, which are in great demand for designing next-generation optoelectronic and quantum devices. Full article

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16 pages, 24086 KiB

Open AccessArticle

Crystallization Kinetics: Relationship between Crystal Morphology and the Cooling Rate—Applications for Different Geological Materials

by Namık Aysal, Yiğit Kurt, Hüseyin Öztürk, Gulce Ogruc Ildiz, Mehmet Yesiltas, Davut Laçin, Sinan Öngen, Timur Nikitin and Rui Fausto

Crystals 2023, 13(7), 1130; https://doi.org/10.3390/cryst13071130 - 19 Jul 2023

Cited by 3 | Viewed by 3256

Abstract

Crystal morphology is controlled by several physicochemical parameters such as the temperature, pressure, cooling rate, nucleation, diffusion, volatile composition, and viscosity. The development of different crystal morphologies is observed as a function of the cooling rate in many different rock types (i.e., glassy [...] Read more.

Crystal morphology is controlled by several physicochemical parameters such as the temperature, pressure, cooling rate, nucleation, diffusion, volatile composition, and viscosity. The development of different crystal morphologies is observed as a function of the cooling rate in many different rock types (i.e., glassy volcanic rocks, and archeometallurgical slags). Crystallization is a two-stage kinetic process that begins with the formation of a nucleus and then continues with the accumulation of ions on it. The shapes of the crystals depend on the degree of undercooling (ΔT), and euhedral crystals, having characteristic forms that reflect their crystallographic internal structure, that grow just below their liquidus temperature. In this study, crystal morphologies in different minerals (e.g., quartz, sanidine, olivine, pyroxene, magnetite, etc.) that had developed in silicic volcanic rocks (spherulites) and slags from ancient mining were investigated and characterized using optical microscopy, X-ray diffraction, and Fourier-transform infrared (FTIR), Raman, and scanning electron microscope-energy dispersive X-ray fluorescence (SEM-EDX) spectroscopic techniques. Depending on the increase in the cooling rate, quartz, feldspar, olivine, pyroxene, and magnetite minerals were found to crystallize in subhedral, skeletal, dendritic, spherical, bow-tie and fibrous forms in glassy volcanic rocks and archeometallurgical slags. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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14 pages, 6410 KiB

Open AccessArticle

Synthesis, Characterization and DFT Calculation of Naphthalene-Based Crystal Structure with Pyridylimine-Binding Units

by Babak Mirtamizdoust, Amirhossein Karamad, Negin Rahmani, Younes Hanifehpour and Sang Woo Joo

Crystals 2023, 13(7), 1129; https://doi.org/10.3390/cryst13071129 - 19 Jul 2023

Viewed by 1236

Abstract

This study focuses on the synthesis, characterization, and properties of a yellowish, prism-shaped ligand, N,N′-(naphthalene-1,5-diyl) bis(1-(pyridin-2-yl) methanimine). The ligand was synthesized through refluxing 1,5-diaminonaphthalene and pyridine-2-carbaldehyde in extra-pure ethanol, employing X-ray diffraction on single crystal. The crystal is structured with two pyridylimine-binding units [...] Read more.

This study focuses on the synthesis, characterization, and properties of a yellowish, prism-shaped ligand, N,N′-(naphthalene-1,5-diyl) bis(1-(pyridin-2-yl) methanimine). The ligand was synthesized through refluxing 1,5-diaminonaphthalene and pyridine-2-carbaldehyde in extra-pure ethanol, employing X-ray diffraction on single crystal. The crystal is structured with two pyridylimine-binding units linked to a naphthalene. The crystal has a P2₁/c space group in a monoclinic system. The structure was confirmed through an infrared examination. Computational spectroscopy and theoretical methods were used to investigate the ligand HOMO, LUMO, and charge distribution. Additionally, a Hirshfeld analysis was performed to investigate noncovalent interactions in the crystalline form. The results showed that dispersion forces (H···H) were the primary factor contributing to the arrangement of the ligand molecule, accounting for 45.3% of the total interactions in the absence of hydrogen bonding. Overall, this study provides valuable insights into the synthesis, characterization, and properties of this unique ligand. Full article

(This article belongs to the Section Organic Crystalline Materials)

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20 pages, 8119 KiB

Open AccessArticle

Crystal Structure of Bismuth-Containing Samarium Iron–Aluminium Borates Sm_1−xBi_xFe_3−yAl_y(BO₃)₄ (x = 0.05–0.07, y = 0–0.28) in the Temperature Range of 25–500 K

by Ekaterina S. Smirnova, Olga A. Alekseeva, Vladimir V. Artemov, Timofei A. Sorokin, Dmitry N. Khmelenin, Ekaterina V. Sidorova, Kirill V. Frolov and Irina A. Gudim

Crystals 2023, 13(7), 1128; https://doi.org/10.3390/cryst13071128 - 19 Jul 2023

Viewed by 1123

Abstract

Structural features of new mixed bismuth-containing samarium iron–aluminium borate single crystals Sm_1−xBi_xFe_3−yAl_y(BO₃)₄ (x = 0.05–0.07, y = 0–0.28) were studied using X-ray diffraction analysis based on aluminium content and [...] Read more.

Structural features of new mixed bismuth-containing samarium iron–aluminium borate single crystals Sm_1−xBi_xFe_3−yAl_y(BO₃)₄ (x = 0.05–0.07, y = 0–0.28) were studied using X-ray diffraction analysis based on aluminium content and temperature in the range 25–500 K. The crystals were grown using the solution-in-melt technique with Bi₂Mo₃O₁₂ in a flux. The composition of the single crystals was analyzed using energy-dispersive X-ray fluorescence and energy-dispersive X-ray elemental analysis. Temperature dependencies of Sm_1−xBi_xFe_3−yAl_y(BO₃)₄ unit-cell parameters were studied. Negative thermal expansion was identified below 100 K and represented by characteristic surfaces of the thermal expansion tensor. (Sm,Bi)–O, (Sm,Bi)–(Fe,Al), (Fe,Al)–(Fe,Al), and (Fe,Al)–O interatomic distances decreased with the addition of aluminium atoms. An increase in the (Fe,Al)–(Fe,Al) intrachain bond length at low temperatures in the magnetically ordered state weakened this bond, whereas a decrease in the (Fe,Al)–(Fe,Al) interchain distance strengthened super-exchange paths between different chains. It was found that the addition of aluminium atoms influenced interatomic distances in Sm_1−xBi_xFe_3−yAl_y(BO₃)₄ much more than lowering the temperature from 293 K to 25 K. The effect of aluminium doping on magnetoelectric properties and structural symmetry of rare-earth iron borates is also discussed. Full article

(This article belongs to the Special Issue Recent Developments of Crystallography in RAS (Russian Academy of Sciences))

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13 pages, 9550 KiB

Open AccessArticle

Piranha Solution-Assisted Surface Engineering Enables Silicon Nanocrystals with Superior Wettability and Lithium Storage

by Tingting Li, Yangfan Li, Fan Zhang, Naiwen Liang, Jiang Yin, Haihong Zhao, Yahui Yang, Bo Chen and Lishan Yang

Crystals 2023, 13(7), 1127; https://doi.org/10.3390/cryst13071127 - 19 Jul 2023

Cited by 2 | Viewed by 2156

Abstract

Silicon anodes with a high theoretical capacity possess great potential applications in power batteries for electric vehicles, while their volume expansion always leads to crystal pulverization and electrode polarization. An ideal solution to alleviate such pulverization and polarization of silicon crystals is to [...] Read more.

Silicon anodes with a high theoretical capacity possess great potential applications in power batteries for electric vehicles, while their volume expansion always leads to crystal pulverization and electrode polarization. An ideal solution to alleviate such pulverization and polarization of silicon crystals is to simultaneously use nano-sized silicon crystals and introduce high viscosity and elasticity polymer binders. This work has achieved the adjustable introduction of hydroxyl groups to silicon nanocrystals under the optimal reaction temperature (e.g., 80 °C) and appropriate piranha solution composition (e.g., H₂SO₄/H₂O₂ = 3:1 v/v), ultimately forming an amorphous coating layer of ~1.3 nm on the silicon surface. The optimized silicon anode exhibits superior electrochemical performance (with an initial Coulombic efficiency of 85.5%; 1121.4 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles) and improved hydrophilicity. The introduced hydroxyl groups significantly enhance the hydrophilicity of silicon in the electrolyte and the electrochemical activity of the silicon anodes. The hydroxyl groups achieve stronger bonding between silicon and polymer binders, ultimately improving the mechanical strength and stability of the electrode. The introduction of hydrophily functional groups on the surface of silicon crystals can be explored as an active strategy to solve the above issues. This surface engineering method could be extended to more fields of infiltrating silicon-based functional materials. Full article

(This article belongs to the Special Issue Emerging Low-Dimensional Materials II)

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13 pages, 4622 KiB

Open AccessArticle

Preparation and Investigation of Micro-Transfer-Printable Single-Crystalline InP Coupons for Heterogeneous Integration of III-V on Si

by Isabella Peracchi, Carsten Richter, Tobias Schulz, Jens Martin, Albert Kwasniewski, Sebastian Kläger, Christiane Frank-Rotsch, Patrick Steglich and Karoline Stolze

Crystals 2023, 13(7), 1126; https://doi.org/10.3390/cryst13071126 - 19 Jul 2023

Viewed by 1628

Abstract

New requirements for high-frequency applications in wireless communication and sensor technologies need III-V compound semiconductors such as indium phosphide (InP) to complement silicon (Si)-based technologies. This study establishes the basis for a new approach to heterogeneous integration of III-V on Si aimed at [...] Read more.

New requirements for high-frequency applications in wireless communication and sensor technologies need III-V compound semiconductors such as indium phosphide (InP) to complement silicon (Si)-based technologies. This study establishes the basis for a new approach to heterogeneous integration of III-V on Si aimed at the transfer of single-crystalline InP coupons on Si via micro-transfer printing (μTP). The InP coupons will act as high-quality virtual substrates that allow selective homo-epitaxy. We present the chemical-mechanical polishing-based preparation and structural characterization of µm-thin (001) InP platelets, starting from high-quality 4-inch bulk crystals and micro-patterning into transferable coupons of several hundred µm². The obtained InP platelets exhibit the desired thickness—below 10 ± 1 µm—and low surface roughness—<0.3 nm—on both sides, meeting the precondition for µTP and epitaxy. X-ray rocking curve measurements provide accurate spatial maps of the total strain, which indicate small strain variations in the µm-thin InP sample. Rocking curve mappings of the (0 0 4) reflection reveal half-widths below 16 arcsec in the majority of the sample area after thinning that is similar to commercially available InP bulk substrates. Pole figure measurements show no evidence of stress-induced micro-twinning or stacking faults. Overall, minor indications of crystal quality degradation in the product platelets, compared with the bulk samples, were detected. Full article

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12 pages, 3388 KiB

Open AccessArticle

Secondary Phase CeO₂ Precipitates in Ce,Er-Doped Na_0.5La_0.5MoO₄ Single Crystals Grown by Czochralski Method

by Elena I. Suvorova, Kirill A. Subbotin, Denis A. Lis, Evgeny V. Zharikov and Philippe A. Buffat

Crystals 2023, 13(7), 1125; https://doi.org/10.3390/cryst13071125 - 19 Jul 2023

Viewed by 1214

Abstract

Analytical scanning and transmission electron microscopy were used to study the microstructure of Ce,Er-doped Na_0.5La_0.5MoO₄ laser crystals. Crystals were grown by the Czochralski method from the melts with a nominal composition of Na_0.5La_0.5−xCe_x [...] Read more.

Analytical scanning and transmission electron microscopy were used to study the microstructure of Ce,Er-doped Na_0.5La_0.5MoO₄ laser crystals. Crystals were grown by the Czochralski method from the melts with a nominal composition of Na_0.5La_0.5−xCe_xEr_0.005MoO₄, where x = 0.125 and 0.15, then annealed at 700 and 1000 °C in the oxidizing atmosphere. We found the secondary phase precipitation of Ce₂O₃ oxide in as-grown crystals, while after high-temperature annealing the CeO₂ precipitated crystals are always observed. Impurity ions Ce³⁺ occupy the La sites, and approximately 20% of the nominal Ce content is involved in the formation of Ce oxide secondary phase precipitates. The length of CeO₂ precipitated crystals ranged between 100 nm and 550 nm (average length was 200 nm) and their width was 30–70 nm. The mechanism of CeO₂ formation is discussed. The orientation relationships of Na_0.5La_0.5−xCe_xEr_0.005MoO₄/CeO₂, the degree of coherence of the interface, and the preferential directions of their growth in the matrix were established. CeO₂ crystals precipitated in the matrix cause light scattering with a wavelength comparable to the size of the precipitates and lead to deterioration of optical transparency of the material. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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12 pages, 3628 KiB

Open AccessArticle

The Optimization of NiO Doping, Thickness, and Extension in kV-Class NiO/Ga₂O₃ Vertical Rectifiers

by Chao-Ching Chiang, Jian-Sian Li, Hsiao-Hsuan Wan, Fan Ren and Stephen J. Pearton

Crystals 2023, 13(7), 1124; https://doi.org/10.3390/cryst13071124 - 19 Jul 2023

Cited by 5 | Viewed by 1679

Abstract

Ga₂O₃ heterojunction rectifiers have emerged as a novel candidate for various power conversion applications by using NiO as the solution on the p-type side. In this work, the optimized design of high-breakdown (1–7 kV), vertical geometry NiO/Ga₂O₃ [...] Read more.

Ga₂O₃ heterojunction rectifiers have emerged as a novel candidate for various power conversion applications by using NiO as the solution on the p-type side. In this work, the optimized design of high-breakdown (1–7 kV), vertical geometry NiO/Ga₂O₃ rectifiers was examined using the Silvaco TCAD simulator to determine the electric field distribution for different NiO parameters. The doping concentration (10¹⁷–10¹⁹ cm⁻³), thickness (10–70 nm) of the guard ring, and its extension beyond the anode (0–30 µm) are all important in determining where the device breakdown occurs. Spatially, this can vary from the edge of the bilayer NiO extension to directly at the periphery of the top contact, consistent with experimental results. This transition phenomenon is proven to be correlated with the depletion effect by monitoring the depletion width when ramping up the bias and the doping concentration. The breakdown voltage was also calculated as a function of NiO top and bottom layer thicknesses and the doping concentration under different critical breakdown fields, where the latter is determined by the material quality of the drift layer. Full article

(This article belongs to the Special Issue β-Ga₂O₃: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties)

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13 pages, 6971 KiB

Open AccessArticle

Layered Epitaxial Growth of 3C/4H Silicon Carbide Confined by Surface Micro-Nano Steps

by Ning Guo, Yicheng Pei, Weilong Yuan, Yunkai Li, Siqi Zhao, Shangyu Yang, Yang Zhang and Xingfang Liu

Crystals 2023, 13(7), 1123; https://doi.org/10.3390/cryst13071123 - 19 Jul 2023

Cited by 2 | Viewed by 1943

Abstract

In this study, we used a horizontal hot-wall CVD epitaxy apparatus to grow epitaxial layers on 4° off-axis 4H-SiC substrates. Epitaxial films were grown by adjusting the flow rate of the source gas at different levels. With an increase in the source gas [...] Read more.

In this study, we used a horizontal hot-wall CVD epitaxy apparatus to grow epitaxial layers on 4° off-axis 4H-SiC substrates. Epitaxial films were grown by adjusting the flow rate of the source gas at different levels. With an increase in the source gas flow rate, a notable transition in the crystalline structure of the epitaxial layer was observed, gradually shifting from 4H-SiC to 3C-SiC. Furthermore, the quality of the epitaxial layer correspondingly exhibited degradation. Specifically, for epitaxial films grown under moderate gas flow rates, the central region demonstrated a crystalline structure of 4H-SiC, while the outer ring region exhibited a crystalline structure of 3C-SiC. Using a scanning electron microscope (SEM) to observe the transition zone of the two regions, a region of 3C/4H overlapping growth below it was found. Bright areas corresponded to 3C, while dark areas corresponded to 4H, as confirmed by Raman spectroscopy and other SEM images. The growth interfaces of the two crystal types were clearly discernible and relatively compact. Furthermore, the growth angles of the two crystal types and their correlation with the cutting direction strongly suggest that this overlap is related to the formation of micro-nano steps on the substrate surface. Full article

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

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