Previous Issue
Volume 14, June
 
 

Crystals, Volume 14, Issue 7 (July 2024) – 71 articles

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Select all
Export citation of selected articles as:
19 pages, 10752 KiB  
Review
Synthesis, Characterisation, and Applications of TiO and Other Black Titania Nanostructures Species (Review)
by Simonas Ramanavicius and Arunas Jagminas
Crystals 2024, 14(7), 647; https://doi.org/10.3390/cryst14070647 (registering DOI) - 14 Jul 2024
Viewed by 123
Abstract
Black titania, a conductive ceramic material class, has garnered significant interest due to its unique optical and electrochemical properties. However, synthesising and properly characterising these structures pose a considerable challenge. This diverse material family comprises various titanium oxide phases, many of them non-stoichiometric. [...] Read more.
Black titania, a conductive ceramic material class, has garnered significant interest due to its unique optical and electrochemical properties. However, synthesising and properly characterising these structures pose a considerable challenge. This diverse material family comprises various titanium oxide phases, many of them non-stoichiometric. The term “black TiO2” was first introduced in 2011 by Xiaobo Chen, but Arne Magneli’s groundbreaking discovery and in-depth investigation of black titania in 1957 laid the foundation for our understanding of this material. The non-stoichiometric black titanium oxides were then called the Magneli phases. Since then, the science of black titania has advanced, leading to numerous applications in photocatalysis, electrocatalysis, supercapacitor electrodes, batteries, gas sensors, fuel cells, and microwave absorption. Yet, the literature is rife with conflicting reports, primarily due to the inadequate analysis of black titania materials. This review aims to provide an overview of black titania nanostructures synthesis and the proper characterisation of the most common and applicable black titania phases. Full article
Show Figures

Figure 1

11 pages, 3629 KiB  
Article
Thermal Behavior of Clinoptilolite
by Magdalena Król, Jakub Dechnik, Patryk Szymczak, Bartosz Handke, Magdalena Szumera and Paweł Stoch
Crystals 2024, 14(7), 646; https://doi.org/10.3390/cryst14070646 (registering DOI) - 14 Jul 2024
Viewed by 122
Abstract
Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to [...] Read more.
Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to 1200 °C, with results analyzed based on its crystal structure. Principal components analysis (PCA) of the DRIFT spectra indicated progressive water removal and dehydration upon heating, leading to the formation of hydrogen bonds. Thermogravimetric analysis (TGA) revealed a two-step endothermic weight loss: initially, physically adsorbed water was lost up to 100 °C, followed by the removal of tightly bound water and hydroxyl groups until 800 °C. Clinoptilolite remained the dominant phase up to 800 °C, after which albite and cristobalite took over. Rietveld refinement showed that the sample initially contained 70% clinoptilolite, 24% albite, and 6% cristobalite. Above 800 °C, clinoptilolite disappeared, leaving 93% albite and 7% cristobalite. FT-IR spectra changes due to water loss were evident: drying of adsorbed water occurred up to 75 °C and minimal changes were observed from 75 °C to 135 °C, followed by further dehydration until 240 °C. Complete dehydration was confirmed by the disappearance of OH stretching vibration bands by 395 °C, consistent with TGA findings. Full article
(This article belongs to the Section Hybrid and Composite Crystalline Materials)
Show Figures

Figure 1

17 pages, 5191 KiB  
Article
Density Functional Theory Calculations for Interpretation of Infra-Red Spectra of Liquid Crystalline Chiral Compound
by Aleksandra Deptuch, Natalia Górska, Michaela Murzyniec, Monika Srebro-Hooper, James Hooper, Magdalena Dziurka and Magdalena Urbańska
Crystals 2024, 14(7), 645; https://doi.org/10.3390/cryst14070645 (registering DOI) - 13 Jul 2024
Viewed by 264
Abstract
The experimental IR spectra of (S)-4′-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[2-(2,2,3,3,4,4,4-heptafluorobutoxy) ethyl-1-oxy]-2-fluorobenzoate in the crystal phase are analyzed with the help of dispersion-corrected density functional theory (DFT+D3) calculations for isolated molecular monomer and dimer models, and a periodic model computed at the extended density [...] Read more.
The experimental IR spectra of (S)-4′-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[2-(2,2,3,3,4,4,4-heptafluorobutoxy) ethyl-1-oxy]-2-fluorobenzoate in the crystal phase are analyzed with the help of dispersion-corrected density functional theory (DFT+D3) calculations for isolated molecular monomer and dimer models, and a periodic model computed at the extended density functional tight-binding (xTB) level of theory. It is found that the frequency scaling coefficients obtained with the results of the molecular calculations are good matches for the crystal phase, being close to 1. The molecular and periodic models both confirm that varied intra- and intermolecular interactions are crucial in order to reproduce the broadened shape of the experimental band related to C=O stretching; the key factors are the conjugation of the ester groups with the aromatic rings and the varied intermolecular chemical environments, wherein the C=O group that bridges the biphenyl and F-substituted phenyl groups seems particularly sensitive. The C=O stretching vibrations are investigated as a function of temperature, covering the range of the crystal, smectic CA*, smectic C* and isotropic liquid phases. The structure changes are followed based on the X-ray diffraction patterns collected in the same temperatures as the IR spectra. The experimental and computational results taken together indicate that the amount of weak C=O…H-C hydrogen bonds between the molecules in the smectic layers decreases with increasing temperature. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
19 pages, 3750 KiB  
Article
Visible-Light Spectroscopy and Rock Magnetic Analyses of Iron Oxides in Mixed-Mineral Assemblages
by Christopher J. Lepre, Owen M. Yazzie and Benjamin R. Klaus
Crystals 2024, 14(7), 644; https://doi.org/10.3390/cryst14070644 (registering DOI) - 13 Jul 2024
Viewed by 173
Abstract
Iron oxide assemblages are central to many pursuits, ranging from Mars exploration to environmental remediation. Oxides and oxyhydroxides of iron both carry the special properties of color and magnetism. In this paper, we use visible-light spectroscopy and rock magnetic data collected at varying [...] Read more.
Iron oxide assemblages are central to many pursuits, ranging from Mars exploration to environmental remediation. Oxides and oxyhydroxides of iron both carry the special properties of color and magnetism. In this paper, we use visible-light spectroscopy and rock magnetic data collected at varying temperatures (~77–973 K) to analyze the concentrations and identities of iron oxides found in natural hematite-dominated samples that were obtained from a scientific drill core of Late Triassic red beds in the American Southwest. Our results suggest that hematite colorization of Earth materials varies from red to blue/purple as crystal size increases. Second-derivative analysis of the collected visible-light spectra allows this variation to be measured through the characteristic wavelength band position. Magnetic coercivity data indicate “hardness” differences that also may suggest smaller grain sizes are associated with redder colors. Yellowish maghemite and goethite have overlapping characteristic wavelength band positions that make it challenging to distinguish their contributions to mixed assemblages from visible-light data alone. Remanent magnetizations acquired at ~77 K and room temperature suggest the presence of hematite and a low-coercivity phase that may be maghemite and/or oxidized magnetite. However, we interpret this phase as maghemite in order to explain the changes in iron oxide concentrations indicated by visible-light intensities near ~425 nm and because the thermal demagnetization data suggest that goethite is absent from the samples. Future research that increases the resolution of hematite, maghemite, and goethite detection in experimental and natural samples will provide opportunities to refine the study of past climates and constrain soil iron availability under future changes in global moisture and temperature. Multimethod datasets improve understanding of environmental conditions that cause iron oxides assemblages to shift in phase dominance, grain size, and crystallinity. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
Show Figures

Figure 1

18 pages, 1255 KiB  
Article
The Influence of Process Parameters on the Microstructure and Microhardness of 304 Stainless Steel in Joule Heating Fused Filament Fabrication
by Suli Li, Jichao Chen, Longfei Fan, Jie Xiong, Zhuang Gao and Laixia Yang
Crystals 2024, 14(7), 643; https://doi.org/10.3390/cryst14070643 - 12 Jul 2024
Viewed by 169
Abstract
Using finite element simulation and single-variable experimental methods, this study analyzes the variations in the microstructure and hardness of a 304 stainless steel wire during Joule heating fused filament fabrication. The effects of current intensity, printing speed, and roller pressure on the macroscopic [...] Read more.
Using finite element simulation and single-variable experimental methods, this study analyzes the variations in the microstructure and hardness of a 304 stainless steel wire during Joule heating fused filament fabrication. The effects of current intensity, printing speed, and roller pressure on the macroscopic morphology, microstructure, and microhardness of a single-layer single-channel formation were investigated. The results indicate that when the current intensity is 400 A, the printing speed is 1000 mm/min, and the roller pressure is 0.3 N, the surface of the single-layer single-channel formation is smooth and exhibits optimal forming characteristics with a width-to-height ratio of 3.23, a dilution rate of 51.61%, and an average microhardness of 238.17 HV. As the current intensity increases, the microstructure in the fusion zone initially decreases in size and then increases; similarly, with the increase in printing speed, the microstructure in the fusion zone first decreases and then increases; as the roller pressure increases, the microstructure in the fusion zone initially increases in size and then decreases. The microhardness initially increases and then decreases with the increase in process parameters, resulting in uneven hardness distribution due to the variations in microstructure size. The optimal combination of process parameters achieves a balance between heat input, cooling rate, and growth rate, thereby achieving grain refinement and hardness improvement, ultimately enhancing the mechanical properties of the material. Full article
17 pages, 4144 KiB  
Article
Study of the Influence of the Change from Methyl to Isopropyl Substituents in 1-(2,4,6-trialkylphenyl)ethanol on the Point Group Symmetry of the 0-D Hydrogen-Bonded Moiety
by Ewa M. Iwanek (nee Wilczkowska) and Marek Gliński
Crystals 2024, 14(7), 642; https://doi.org/10.3390/cryst14070642 - 12 Jul 2024
Viewed by 196
Abstract
The steric hindrance in molecules of 1-(2,4,6-trimethylphenyl)ethanone and 1-(2,4,6-triisopropylphenyl)ethanone were shown to substantially differentiate the options of synthesis of the respective alcohols. The former was obtained with a yield of 12% with a mild reducing agent, i.e., NaBH4, as well as [...] Read more.
The steric hindrance in molecules of 1-(2,4,6-trimethylphenyl)ethanone and 1-(2,4,6-triisopropylphenyl)ethanone were shown to substantially differentiate the options of synthesis of the respective alcohols. The former was obtained with a yield of 12% with a mild reducing agent, i.e., NaBH4, as well as in vapor phase transfer hydrogenation (22% yield at 673 K) over MgO, whereas the latter was not formed at all under those conditions. The only agent that was able to reduce both ketones was LiAlH4. The single crystals of the two alcohols were obtained and their structures were determined. The symmetry of the 0-D hydrogen-bonded networks of molecules in these crystals was analyzed. It was shown that the methyl substituent allows the molecules to form hexameric rings, whereas the isopropyl-substituted molecules formed tetrameric ones. In both cases, there were two types of rings in the cell, but four types of molecules forming tetramers and only three types of molecules in the hexamers. These structures were compared to similar structures formed by other molecules found in the Cambridge Structural Database via hydrogen bonding. Moreover, the single crystal of 1-(2,4,6-triisopropylphenyl)ethanone was obtained to explain if either the hydrogen bonding or the presence of isopropyl groups influences the angles in the molecules. Full article
(This article belongs to the Section Organic Crystalline Materials)
Show Figures

Figure 1

13 pages, 1543 KiB  
Article
Computational Study of Molecular Interactions in ZnCl2(urea)2 Crystals as Precursors for Deep Eutectic Solvents
by Adrian Malinowski and Maciej Śmiechowski
Crystals 2024, 14(7), 641; https://doi.org/10.3390/cryst14070641 - 11 Jul 2024
Viewed by 224
Abstract
Deep eutectic solvents (DESs) are now enjoying an increased scientific interest due to their interesting properties and growing range of possible applications. Computational methods are at the forefront of deciphering their structure and dynamics. Type IV DESs, composed of metal chloride and a [...] Read more.
Deep eutectic solvents (DESs) are now enjoying an increased scientific interest due to their interesting properties and growing range of possible applications. Computational methods are at the forefront of deciphering their structure and dynamics. Type IV DESs, composed of metal chloride and a hydrogen bond donor, are among the less studied systems when it comes to their understanding at a molecular level. An important example of such systems is the zinc chloride–urea DES, already used in chemical synthesis, among others. In this paper, the ZnCl2(urea)2 crystal is studied from the point of view of its structure, infrared spectrum, and intermolecular interactions using periodic density functional theory and non-covalent interactions analysis. The two main structural motifs found in the crystal are a strongly hydrogen-bonded urea dimer assisted by chloride anions and a tetrahedral Zn(II) coordination complex. The crystal is composed of two interlocking parallel planes connected via the zinc cations. The infrared spectrum and bond lengths suggest a partially covalent character of the Zn-Cl bonds. The present analysis has far-reaching implications for the liquid ZnCl2–urea DES, explaining its fluidity, expected microstructure, and low conductivity, among others. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
13 pages, 3912 KiB  
Article
A Portable Miniature Cryogenic Environment for In Situ Neutron Diffraction
by Yan Chen, Dunji Yu and Ke An
Crystals 2024, 14(7), 640; https://doi.org/10.3390/cryst14070640 - 11 Jul 2024
Viewed by 204
Abstract
Neutron diffraction instruments offer a platform for materials science and engineering studies at extended temperature ranges far from ambient. As one of the widely used neutron sample environment types, cryogenic furnaces are usually bulky and complex, and they may need hours of beamtime [...] Read more.
Neutron diffraction instruments offer a platform for materials science and engineering studies at extended temperature ranges far from ambient. As one of the widely used neutron sample environment types, cryogenic furnaces are usually bulky and complex, and they may need hours of beamtime overhead for installation, configuration, cooling, and sample change, etc. To reduce the overhead time and expedite experiments at the state-of-the-art high-flux neutron source, we developed a low-cost, miniature, and easy-to-use cryogenic environment (77–473 K) for in situ neutron diffraction. A travel-size mug serves for the environment where the samples sit inside. Immediate cooling and an isothermal dwell at 77 K are realized on the sample by direct contact with liquid N2 in the mug. The designed Al inserts serve as the holder of samples and heating elements, alleviate the thermal gradient, and clear neutron pathways. Both a single-sample continuous measurement and multi-sample high-throughput measurements are demonstrated in this environment. High-quality and refinable in situ neutron diffraction patterns are acquired on model materials. The results quantify the orthorhombic-to-cubic phase transformation process in LiMn2O4 and differentiate the anisotropic lattice thermal expansions and bond length evolutions between rhombohedral perovskite oxides with composition variation. Full article
(This article belongs to the Section Crystal Engineering)
Show Figures

Figure 1

10 pages, 3878 KiB  
Article
Study on Spectral Properties and Mid-Infrared Laser Performance of Er, La:CaF2 Crystals
by Zhen Zhang, Jingjing Liu, Yunfei Wang, Fengkai Ma, Shaochen Liu, Zhonghan Zhang, Jie Liu and Liangbi Su
Crystals 2024, 14(7), 639; https://doi.org/10.3390/cryst14070639 - 11 Jul 2024
Viewed by 213
Abstract
Er3+-doped fluorite crystals, including CaF2 and SrF2, are considered as attractive laser gain materials in the mid-infrared (MIR) region with merits of high laser efficiency as well as low doping concentration. In this work, a series of Er, [...] Read more.
Er3+-doped fluorite crystals, including CaF2 and SrF2, are considered as attractive laser gain materials in the mid-infrared (MIR) region with merits of high laser efficiency as well as low doping concentration. In this work, a series of Er, La:CaF2 crystals were grown and the modulation effect of co-doping La3+ ions on the spectral properties and mid-infrared laser performance was investigated. It was found that introducing La3+ ions can effectively manipulate the coordination environment of Er3+ ions embedded in CaF2 crystal, thus modulating the shape and intensity of absorption and emission bands. On the other hand, La3+ ions can partially substitute Er3+ sites in the clusters to form mixed clusters, which affects the energy transfer processes between Er3+ ions as well as ~3 μm laser performance, which is dominated by energy transfer up-conversion (ETU) processes between Er3+ ions. By co-doping La3+ ions into Er:CaF2 crystal at an appropriate concentration, the spectral parameter modulation can be achieved while maintaining a high MIR laser efficiency. Full article
(This article belongs to the Special Issue Photoelectric Functional Crystals)
Show Figures

Figure 1

11 pages, 3235 KiB  
Article
Effect of Solid/Liquid and Eutectic Front Velocities on Microstructure Evolution in Al-20%Cu Alloys
by Alaaldeen Abdallah, András Roósz, Arnold Rónaföldi and Zsolt Veres
Crystals 2024, 14(7), 638; https://doi.org/10.3390/cryst14070638 - 10 Jul 2024
Viewed by 232
Abstract
During the solidification process, microstructures are affected by the experimental conditions, the thermophysical characteristics of the alloy, and the type of grain-refining particles. Unidirectional solidification experiments were performed in a vertical Bridgman-type furnace to investigate the effect of the solidification front velocity on [...] Read more.
During the solidification process, microstructures are affected by the experimental conditions, the thermophysical characteristics of the alloy, and the type of grain-refining particles. Unidirectional solidification experiments were performed in a vertical Bridgman-type furnace to investigate the effect of the solidification front velocity on the solidified microstructure of a non-refined and refined Al-20%Cu alloy. The samples were solidified by rapidly increasing the sample velocity (v) range from 0.02 mm/s to 0.2 mm/s while maintaining an almost constant temperature gradient (~5 K/mm). As a result, despite changes in the solid/liquid front velocity along the sample, the microstructure of the non-refined alloys remained columnar. In the refined alloy, the columnar structure changed into an equiaxed structure at two different front velocities. Full article
Show Figures

Figure 1

15 pages, 19650 KiB  
Article
Gemological Characteristics of Blue-Violet Cordierite
by Wenjie Yan, Zhiyi Zhou, Yinghua Rao and Qingfeng Guo
Crystals 2024, 14(7), 637; https://doi.org/10.3390/cryst14070637 - 10 Jul 2024
Viewed by 192
Abstract
Cordierite is a violet-blue gem mineral primarily composed of magnesium aluminum silicate. This study employed three samples of Mg-cordierite and conducted tests on their gemological characteristics, spectroscopic features, and chemical composition using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet spectrophotometry, X-ray photoelectron [...] Read more.
Cordierite is a violet-blue gem mineral primarily composed of magnesium aluminum silicate. This study employed three samples of Mg-cordierite and conducted tests on their gemological characteristics, spectroscopic features, and chemical composition using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet spectrophotometry, X-ray photoelectron spectroscopy (XPS), and electron microprobe. The study also explored and analyzed the polychroism and coloration mechanisms of the samples. The results indicate that the lattice vibrations of the Mg-cordierite samples differ along the directions parallel to the a, b, and c crystallographic axes, leading to certain variations in spectral characteristics among these directions. The article provides experimental evidence for the reasons for the polychroism of cordierite in different crystal axes, which is of great significance in the quality evaluation of cordierite. Full article
(This article belongs to the Section Mineralogical Crystallography and Biomineralization)
Show Figures

Figure 1

10 pages, 2125 KiB  
Article
Effect of Acetylation on the Morphology and Thermal Properties of Maize Stalk Cellulose Nanocrystals: A Comparative Study of Green-Extracted CNC vs. Acid Hydrolysed Followed by Acetylation
by Nduduzo Lungisani Khumalo, Samson Masulubanye Mohomane and Tshwafo E. Motaung
Crystals 2024, 14(7), 636; https://doi.org/10.3390/cryst14070636 - 10 Jul 2024
Viewed by 247
Abstract
This study highlights the advantages of employing acetylation to enhance the morphology and thermal properties of cellulose nanocrystals (CNCs) derived from maize stalks. Utilizing a green synthesis approach for CNC extraction, this research presents a novel comparison between green extracted CNCs, and their [...] Read more.
This study highlights the advantages of employing acetylation to enhance the morphology and thermal properties of cellulose nanocrystals (CNCs) derived from maize stalks. Utilizing a green synthesis approach for CNC extraction, this research presents a novel comparison between green extracted CNCs, and their acid hydrolysed, followed by their acetylated counterparts (ACCNCs). This comparison reveals significant improvements in the properties of acetylated CNCs over those produced through conventional acid hydrolysis. The study employs advanced characterization techniques, including Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA), to analyze untreated maize stalk extracted cellulose, green extracted CNCs, and acetylated CNCs. FTIR spectroscopy identifies changes in functional groups, underscoring the efficacy of the extraction and modification processes. XRD analysis demonstrates a beneficial transformation from cellulose I to cellulose II allomorphs post-acetylation, with increased crystallinity index values indicating effective removal of amorphous regions. SEM imaging reveals the preservation of rod-like structures in CNCs, while acetylated CNCs exhibit advantageous morphological changes, such as reduced nanocrystal length and increased branching. TGA results show superior thermal stability in green extracted CNCs and favorable thermal degradation behavior in acetylated CNCs. Overall, this study underscores the potential of acetylation to develop sustainable nanomaterials with tailored properties, offering significant advancements for various applications. Emphasizing the advantages of the prepared ACCNCs and the green synthesis method over traditional acid hydrolysis extraction, this research paves the way for innovative applications in diverse fields. Full article
(This article belongs to the Section Hybrid and Composite Crystalline Materials)
Show Figures

Figure 1

18 pages, 4122 KiB  
Article
Crystallization of Calcium Carbonate and Calcium Phosphate Phases in Silica Hydrogel: Morphological and Compositional Characterization
by Nuria Sánchez-Pastor, André Jorge Pinto, Pablo del Buey Fernández and José Manuel Astilleros
Crystals 2024, 14(7), 635; https://doi.org/10.3390/cryst14070635 - 10 Jul 2024
Viewed by 324
Abstract
The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each [...] Read more.
The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each container was filled with 0.5 M CaCl2 and 0.5 M Na2CO3 solutions, which diffused through the gel column over time. Na3PO4 solutions, with 50 and 500 ppm concentrations, were incorporated into the gel in different experiments, resulting in a homogeneous distribution of phosphate concentrations within the diffusion column. After 15- and 30-day incubation periods post-nucleation, the crystals formed in different sections of the gel were carefully extracted and studied with scanning electron microscopy and electron microprobe. Additionally, Raman spectra were collected from the samples using a confocal Raman microscope, providing further insights into their molecular composition and structural properties. The obtained results show that under the induced experimental conditions (i) phosphate incorporates into calcite’s structure, and (ii) the growth of calcium phosphates in the presence of carbonate ions involves the sequential, heterogeneous nucleation of CO3-bearing OCP/HAP-like phases, with Raman spectral characteristics very similar to those of bioapatites. Full article
Show Figures

Figure 1

16 pages, 3509 KiB  
Article
Effect of Active Phase Precursor on Structural, Textural and Catalytic Properties of the Model NiOx/CeO2 System Active in Dry Reforming of Methane
by Piotr Legutko, Marcin Kozieł, Andrzej Kowalczyk, Marek Michalik and Andrzej Adamski
Crystals 2024, 14(7), 634; https://doi.org/10.3390/cryst14070634 - 10 Jul 2024
Viewed by 240
Abstract
The current paper is devoted to the synthesis of ceria-supported nickel-based catalysts starting from different precursors of the nickel active phase. Thermal decomposition of metal-containing precursors, deposited onto stable supports by dry impregnation, belongs to the industrially preferred, simple ways of catalyst preparation. [...] Read more.
The current paper is devoted to the synthesis of ceria-supported nickel-based catalysts starting from different precursors of the nickel active phase. Thermal decomposition of metal-containing precursors, deposited onto stable supports by dry impregnation, belongs to the industrially preferred, simple ways of catalyst preparation. The synthesized series of NiOx/CeO2 catalysts have been tested in dry methane reforming (DMR), in which two greenhouse gases, i.e., CO2 and CH4, are simultaneously converted into syngas. Both reaction progress and stability of the catalyst strongly depend on nickel speciation, which in turn can be determined by the nature of the chosen precursor. Contrary to relatively many studies focused on the importance of synthetic methods and conditions on nickel speciation, the effect of precursor nature on structural, textural, and functional properties of catalytic systems has neither been discussed much nor fully understood. The main goal of this paper was to elucidate the effect of precursors on the properties of NiOx/CeO2. Consequences of the use of various nickel precursors (simple inorganic salts, organometallic complexes, and chelates) have been analyzed in detail from the viewpoint of their beneficial influence on the catalytic performance of NiOx/CeO2 system (containing 3 wt. % of Ni) tested in DMR. Full article
Show Figures

Figure 1

24 pages, 1501 KiB  
Article
Wet Chemical Synthesis of AlxGa1−xAs Nanostructures: Investigation of Properties and Growth Mechanisms
by Yana Suchikova, Sergii Kovachov, Ihor Bohdanov, Marina Konuhova, Yaroslav Zhydachevskyy, Kuat Kumarbekov, Vladimir Pankratov and Anatoli I. Popov
Crystals 2024, 14(7), 633; https://doi.org/10.3390/cryst14070633 - 9 Jul 2024
Viewed by 285
Abstract
This study focuses on the wet chemical synthesis of AlxGa1−xAs nanostructures, highlighting how different deposition conditions affect the film morphology and material properties. Electrochemical etching was used to texture GaAs substrates, enhancing mechanical adhesion and chemical bonding. Various deposition [...] Read more.
This study focuses on the wet chemical synthesis of AlxGa1−xAs nanostructures, highlighting how different deposition conditions affect the film morphology and material properties. Electrochemical etching was used to texture GaAs substrates, enhancing mechanical adhesion and chemical bonding. Various deposition regimes, including voltage switching, gradual voltage increase, and pulsed voltage, were applied to explore their impact on the film growth mechanisms. SEM analysis revealed distinct morphologies, EDX confirmed variations in aluminum content, Raman spectroscopy detected structural disorders, and XRD analysis demonstrated peak position shifts. The findings emphasize the versatility and cost-effectiveness of wet electrochemical methods for fabricating high-quality AlxGa1−xAs films with tailored properties, showing potential for optoelectronic devices, high-efficiency solar cells, and other advanced semiconductor applications. Full article
14 pages, 12082 KiB  
Article
Cluster Odd-Parity Multipoles by Staggered Orbital Ordering in Locally Noncentrosymmetric Crystals
by Satoru Hayami
Crystals 2024, 14(7), 632; https://doi.org/10.3390/cryst14070632 - 9 Jul 2024
Viewed by 210
Abstract
Odd-parity multipoles in crystals manifest themselves not only in their peculiar electronic orderings but also in unconventional parity-violating physical phenomena. We here report the emergence of odd-parity multipoles by considering staggered orbital orderings in a locally noncentrosymmetric crystal system with the global inversion [...] Read more.
Odd-parity multipoles in crystals manifest themselves not only in their peculiar electronic orderings but also in unconventional parity-violating physical phenomena. We here report the emergence of odd-parity multipoles by considering staggered orbital orderings in a locally noncentrosymmetric crystal system with the global inversion center but without the inversion center at each lattice site. We show that various odd-parity multipoles, such as the electric toroidal monopole, electric dipole, and electric toroidal quadrupole, are realized depending on the type of orbital orderings in the one-dimensional zigzag chain. Such odd-parity multipoles give rise to an antisymmetric spin splitting in the electronic band structure with the aid of the relativistic spin–orbit coupling. We also show that similar states with odd-parity multipoles are realized in other locally noncentrosymmetric crystals, such as the two-dimensional honeycomb and three-dimensional diamond structures. Full article
(This article belongs to the Section Crystalline Metals and Alloys)
Show Figures

Figure 1

16 pages, 2499 KiB  
Article
Structural, Vibrational Spectroscopic and Theoretical (DFT) Studies of 4-Chloro- and 5-Chloro-7-azaindole-3-carbaldehydes
by Wiktor Mucha, Julia Bąkowicz, Magdalena Malik and Barbara Morzyk-Ociepa
Crystals 2024, 14(7), 631; https://doi.org/10.3390/cryst14070631 - 9 Jul 2024
Viewed by 248
Abstract
Molecular structures of 5-chloro-7-azaindole-3-carbaldehyde (5Cl7AICA) and 4-chloro-7-azaindole-3-carbaldehyde (4Cl7AICA) were investigated using infrared and Raman spectroscopy supported by density functional theory (DFT) calculations. Theoretical studies were carried out with three DFT methods, which include dispersion corrections: B3LYP-D3, PBE0-D3, and ωB97X-D. A single-crystal X-ray diffraction [...] Read more.
Molecular structures of 5-chloro-7-azaindole-3-carbaldehyde (5Cl7AICA) and 4-chloro-7-azaindole-3-carbaldehyde (4Cl7AICA) were investigated using infrared and Raman spectroscopy supported by density functional theory (DFT) calculations. Theoretical studies were carried out with three DFT methods, which include dispersion corrections: B3LYP-D3, PBE0-D3, and ωB97X-D. A single-crystal X-ray diffraction analysis was performed for 5Cl7AICA. The compound crystallizes in the monoclinic system, space group P21/c, with lattice parameters a = 3.82810(12) Å, b = 12.7330(3) Å, c = 15.9167(5) Å, and β = 94.539(3)°, with Z = 4. Within the crystal lattice, 5Cl7AICA molecules form dimers via dual and strong N1–H1⋅⋅⋅N7′ hydrogen bonds, accompanied by other intermolecular interactions. In the DFT calculations, two types of dimers of the investigated molecules were analyzed: dimer 1, which is present in the crystal structure of 5Cl7AICA, and dimer 2 displaying a 180° rotation of the aldehyde group compared to dimer 1. Computational results indicate that dimer 1 is more stable than dimer 2 for 5Cl7AICA, whereas dimer 2 is more stable than dimer 1 for 4Cl7AICA molecules. Furthermore, experimental and theoretical vibrational spectra were examined to elucidate the influence of internal rotation of the aldehyde group on spectroscopic properties. Full article
(This article belongs to the Section Organic Crystalline Materials)
Show Figures

Figure 1

13 pages, 4443 KiB  
Article
Electronic State-Regulated Magnetic Phenomena in Single-Crystal FeSe
by Eman A. Alghamdi and Refka Sai
Crystals 2024, 14(7), 630; https://doi.org/10.3390/cryst14070630 - 9 Jul 2024
Viewed by 307
Abstract
In contrast to the observed high-temperature superconductivity in monolayer FeSe/SrTiO3 films, akin to CoSb/SrTiO3, the bulk counterpart, FeSe, does not exhibit superconductivity even under elevated pressure, and its magnetic characteristics remain subject to debate. This [...] Read more.
In contrast to the observed high-temperature superconductivity in monolayer FeSe/SrTiO3 films, akin to CoSb/SrTiO3, the bulk counterpart, FeSe, does not exhibit superconductivity even under elevated pressure, and its magnetic characteristics remain subject to debate. This investigation delves into the electrical and magnetic attributes, alongside X-ray photoelectron spectroscopy (XPS) analysis, of FeSe mono-crystal. Magnetic and electrical transport assessments indicate that FeSe demonstrates characteristics of a Pauli paramagnetic metal within non-Fermi liquid traits. XPS analysis further reveals that the Fe and Se pair in FeSe exist in a zero-valence state, forming a predominantly metallic-bonded alloy. The Pauli paramagnetism observed in FeSe is ascribed to its itinerant electrons. The comprehension of the electronic states in FeSe mono-crystal not only clarifies its lack of magnetic characteristics but also paves the way for exploring potential high-temperature superconductivity. Full article
(This article belongs to the Section Materials for Energy Applications)
Show Figures

Figure 1

17 pages, 3025 KiB  
Article
Anion and Cation Co-Doping of NiO for Transparent Photovoltaics and Smart Window Applications
by Chrysa Aivalioti, Emmanouil G. Manidakis, Nikolaos T. Pelekanos, Maria Androulidaki, Katerina Tsagaraki and Elias Aperathitis
Crystals 2024, 14(7), 629; https://doi.org/10.3390/cryst14070629 - 8 Jul 2024
Viewed by 311
Abstract
Materials engineering based on metal oxides for manipulating the solar spectrum and producing solar energy have been under intense investigation over the last years. In this work, we present NiO thin films double doped with niobium (Nb) and nitrogen (N) as cation and [...] Read more.
Materials engineering based on metal oxides for manipulating the solar spectrum and producing solar energy have been under intense investigation over the last years. In this work, we present NiO thin films double doped with niobium (Nb) and nitrogen (N) as cation and anion dopants (NiO:(Nb,N)) to be used as p-type layers in all oxide transparent solar cells. The films were grown by sputtering a composite Ni-Nb target on room-temperature substrates in plasma containing 50% Ar, 25% O2, and 25% N2gases. The existence of Nb and N dopants in the NiO structure was confirmed by the Energy Dispersive X-Ray and X-Ray Photoelectron Spectroscopy techniques. The nominally undoped NiO film, which was deposited by sputtering a Ni target and used as the reference film, was oxygen-rich, single-phase cubic NiO, having a visible transmittance of less than 20%. Upon double doping with Nb and N the visible transmittance of NiO:(Nb,N) film increased to 60%, which was further improved after thermal treatment to around 85%. The respective values of the direct band gap in the undoped and double-doped films were 3.28 eV and 3.73 eV just after deposition, and 3.67 eV and 3.76 eV after thermal treatment. The changes in the properties of the films such as structural disorder, direct and indirect energy band gaps, Urbach tail states, and resistivity were correlated with the incorporation of Nb and N in their structure. The thermally treated NiO:(Nb,N) film was used to form a diode with a spin-coated two-layer, mesoporous on top of a compact, TiO2 film. The NiO:(Nb,N)/TiO2heterojunction exhibited visible transparency of around 80%, showed rectifying characteristics and the diode’s parameters were deduced using the I-V method. The diode revealed photovoltaic behavior upon illumination with UV light exhibiting a short circuit current density of 0.2 mA/cm2 and open-circuit voltage of 500 mV. Improvements of the output characteristics of the NiO:(Nb,N)/TiO2 UV-photovoltaic by proper engineering of the individual layers and device processing procedures are addressed. Transparent NiO:(Nb,N) films can be potential candidates in all-oxide ultraviolet photovoltaics for tandem solar cells, smart windows, and other optoelectronic devices. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental and Solar Energy Applications)
Show Figures

Figure 1

17 pages, 3964 KiB  
Article
Coupling Response of Piezoelectric Semiconductor Composite Fiber under Local Temperature Change
by Chengcheng Liu and Wenjun Wang
Crystals 2024, 14(7), 628; https://doi.org/10.3390/cryst14070628 - 8 Jul 2024
Viewed by 205
Abstract
This paper details the thermal–mechanical–electrical response of a piezoelectric semiconductor (PS) composite fiber composed of a PS layer and two piezoelectric layers under local temperature change. The phenomenological theory of thermal piezoelectric semiconductors (PSs) is adopted to obtain the analytical solution for each [...] Read more.
This paper details the thermal–mechanical–electrical response of a piezoelectric semiconductor (PS) composite fiber composed of a PS layer and two piezoelectric layers under local temperature change. The phenomenological theory of thermal piezoelectric semiconductors (PSs) is adopted to obtain the analytical solution for each field in the composite fiber under local temperature change. Our findings reveal that such temperature fluctuations induce local polarization, leading to the formation of local potential barriers and potential wells that effectively impede the flow of low-energy electrons along the fiber. Furthermore, the initial carrier concentration and geometric parameters of the composite fiber exert significant influence on its individual fields. The results contribute to the structural design and practical application of piezoelectric semiconductor devices. Full article
(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)
Show Figures

Figure 1

12 pages, 2750 KiB  
Article
Mechanically Mixed Thermally Expanded Graphite/Cobalt(II) Perrhenate—Co(ReO4)2—As Electrodes in Hybrid Symmetric Supercapacitors
by Mateusz Ciszewski, Karolina Pianowska, Joanna Malarz, Katarzyna Leszczyńska-Sejda and Lukasz Hawelek
Crystals 2024, 14(7), 627; https://doi.org/10.3390/cryst14070627 - 8 Jul 2024
Viewed by 230
Abstract
A mechanically homogenized composite of expanded graphite and cobalt(II) perrhenate has been described. Cobalt(II) perrhenate was obtained in a reaction of perrhenic acid with cobalt(II) nitrate. A simple mortar homogenization method was used to enhance the intercalation of cobalt species within the carbon [...] Read more.
A mechanically homogenized composite of expanded graphite and cobalt(II) perrhenate has been described. Cobalt(II) perrhenate was obtained in a reaction of perrhenic acid with cobalt(II) nitrate. A simple mortar homogenization method was used to enhance the intercalation of cobalt species within the carbon matrix. The specific capacitance of the composite was enhanced by 50% (to 78 F/g) in comparison to bare expanded graphite (52 F/g). The electrochemical characteristics were significantly improved, including better cyclability (7% capacitance loss), a lower resistance of the electrode material, and a lower iR drop, with respect to expanded graphite without cobalt(II) perrhenate active species. Expanded graphite, with its unique specific surface area and pore size diameter, was proved to be a potential and cheap carbon support. Full article
(This article belongs to the Special Issue Hybrid Materials for Energy Storage and Conversion)
Show Figures

Figure 1

26 pages, 10164 KiB  
Review
The Diversity of MOF Structures and Their Impact on Photoelectrochemical Sensors for Monitoring Environmental Pollution
by Magdalena Luty-Błocho and Agnieszka Podborska
Crystals 2024, 14(7), 626; https://doi.org/10.3390/cryst14070626 - 8 Jul 2024
Viewed by 299
Abstract
The problem of environmental pollution is one of the most important in the modern world. Pollution causes an increase in human diseases, the extinction of many species of plants and animals, global warming, and many weather anomalies. One of the great challenges for [...] Read more.
The problem of environmental pollution is one of the most important in the modern world. Pollution causes an increase in human diseases, the extinction of many species of plants and animals, global warming, and many weather anomalies. One of the great challenges for scientists is the development of methods for monitoring and removing the emerging pollutants. This review focuses on Metal–Organic Frameworks (MOFs) and their use as working material to construct different types of sensors for application in environmental pollution monitoring. In particular, the detection of heavy metals (mercury, lead, and arsenic) and organic compounds (drugs, biomolecules, and pesticides) are considered. The collected data show that photoelectrochemical (PEC) sensors based on MOFs are the most fascinating materials due to various combinations (e.g., surface modification) and operational possibilities. PEC sensors achieve enormous sensitivity, which increases even to the pico level, making it the best tool in sensing applications. This review also highlights the main sensor challenges. Most of them are concerned with the possibility of reusing the sensor, its regeneration, and safe disposal. In addition, more attention should be paid to the sensor manufacturing process, which often uses toxic compounds, and research to eliminate them in favor of non-toxic compounds. Full article
(This article belongs to the Special Issue Electrochemical Materials for the Future of Society)
Show Figures

Figure 1

12 pages, 11793 KiB  
Article
Investigation and Comparison of the Performance for β-Ga2O3 Solar-Blind Photodetectors Grown on Patterned and Flat Sapphire Substrate
by Zuyong Yan, Shan Li, Zeng Liu, Jianying Yue, Xueqiang Ji, Jinjin Wang, Shanglin Hou, Gang Wu, Jingli Lei, Guobin Sun, Peigang Li and Weihua Tang
Crystals 2024, 14(7), 625; https://doi.org/10.3390/cryst14070625 - 7 Jul 2024
Viewed by 380
Abstract
Ga2O3, with its large band gap, is a promising material suitable for utilization in solar-blind photodetection. Sapphire with a higher lattice match with Ga2O3 was used as the substrate for epitaxial growth of Ga2O [...] Read more.
Ga2O3, with its large band gap, is a promising material suitable for utilization in solar-blind photodetection. Sapphire with a higher lattice match with Ga2O3 was used as the substrate for epitaxial growth of Ga2O3. Here, the epitaxial layers of Ga2O3 were deposited by MOCVD on patterned sapphire substrates. The structure of epitaxial Ga2O3 layers on patterned substrates has been identified by X-ray diffractometry. To investigate the influence of the patterned substrates on the formation of epitaxial layers, thin Ga2O3 layers were grown on a flat sapphire substrate under the same conditions. Both types of samples were β-phase. However, no improvement in the layers’ crystalline quality was discovered when utilizing patterned sapphire substrates. In addition, the performance of the obtained two types of Ga2O3 photodetectors was compared. The photoelectric properties, such as responsivity, response speed, and detection capability, were different in the case of flat samples. Full article
(This article belongs to the Special Issue Epitaxial Growth and Application of Metallic Oxide Thin Films)
Show Figures

Figure 1

12 pages, 2435 KiB  
Article
Coercivity of (Fe0.7Co0.3)2B Nanowire and Its Bonded Magnet
by Xubo Liu and Ikenna C. Nlebedim
Crystals 2024, 14(7), 624; https://doi.org/10.3390/cryst14070624 - 6 Jul 2024
Viewed by 226
Abstract
(Fe0.7Co0.3)2B are potential permanent magnets material due to its large saturation magnetization and high Curie temperature. However, it has moderate magnetocrystalline anisotropy (MCA) and low coercivity. One way to improve its coercivity is to combine the contributions [...] Read more.
(Fe0.7Co0.3)2B are potential permanent magnets material due to its large saturation magnetization and high Curie temperature. However, it has moderate magnetocrystalline anisotropy (MCA) and low coercivity. One way to improve its coercivity is to combine the contributions from magnetocrystalline- and magnetic-shape anisotropy by preparing (Fe0.7Co0.3)2B nanowires. We study the effects of size, morphology, and surface defects on the hard magnetic properties of nanowires using micromagnetic simulation. The hard magnetic properties of (Fe0.7Co0.3)2B nanowire-bonded magnets are estimated, including the role of inter-wire magnetostatic interaction. By considering the existence of local reductions in MCA energy of up to 30% on the surface layer of nanowires, the anisotropic bonded magnet with a 65% vol. of (Fe0.7Co0.3)2B nanowires would have typical remanence, Br= 7.6–8.4 kG, coercivity, Hci= 9.6–9.9 kOe, and maximum energy product, (BH)m = 14–17.8 MGOe. Developing effective technology for synthesizing nanowires and fabricating corresponding bonded magnets is promising for manufacturing practical magnets based on the magnetic phase with a relatively low or moderate MCA, such as (Fe0.7Co0.3)2B. Full article
(This article belongs to the Special Issue Magnetoelectric Materials and Their Application)
Show Figures

Figure 1

26 pages, 9403 KiB  
Review
Advanced Preparation Methods for Ceramic Membrane Materials in Electrochemical Applications
by Keqiang Fan, Mengyang Yu, Jincheng Lei and Shenglong Mu
Crystals 2024, 14(7), 623; https://doi.org/10.3390/cryst14070623 - 6 Jul 2024
Viewed by 318
Abstract
The outstanding thermal, chemical, and mechanical properties of ceramic membranes have attracted increasing attention, offering advantages over polymer and metal counterparts. Exploring the specialized applications of ceramic membranes through various preparation methods poses a daunting challenge for contemporary researchers. Traditional preparation methods are [...] Read more.
The outstanding thermal, chemical, and mechanical properties of ceramic membranes have attracted increasing attention, offering advantages over polymer and metal counterparts. Exploring the specialized applications of ceramic membranes through various preparation methods poses a daunting challenge for contemporary researchers. Traditional preparation methods are essentially unable to meet the requirements of complex membrane structures. For instance, in ceramic fuel cell applications, cells composed of ceramic membrane materials exhibit high resistance and low conductivity, which seriously hinders the progress of new high-performance ceramic fuel cells. Therefore, it is necessary to improve preparation methods to improve the electrochemical performance of devices composed of ceramic membrane materials. In recent years, breakthroughs in various new processing technologies have propelled the performance of ceramic membrane devices. This paper will focus on the following aspects. Firstly, traditional preparation methods and advanced preparation methods of ceramic membrane materials will be discussed. Secondly, high-performance ceramic membrane materials prepared by different advanced preparation methods are introduced, and the electrochemical properties of the devices composed of ceramic membrane materials are elaborated in combination with different testing and characterization methods. Finally, the prospects and future direction of the preparation of ceramic membrane materials by advanced preparation methods are summarized. Full article
(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)
Show Figures

Figure 1

3 pages, 673 KiB  
Editorial
One-Dimensional and Two-Dimensional Nanomaterials for Sensor Applications
by Andrew F. Zhou and Peter X. Feng
Crystals 2024, 14(7), 622; https://doi.org/10.3390/cryst14070622 - 6 Jul 2024
Viewed by 397
Abstract
The significance of 1D and 2D nanomaterials in sensor technology lies in their unique properties and the potential for high-performance sensing [...] Full article
(This article belongs to the Special Issue 1D and 2D Nanomaterials for Sensor Applications)
15 pages, 9844 KiB  
Article
Microstructural Evolution and Strengthening of Dual-Phase Stainless Steel S32750 during Heavily Cold Drawing
by Hong Gao, Zhixun An, Liang Yao, Jianyong Wang, Lili Zhai, Binhua Ding, Jin Peng, Lichu Zhou and Xia Cao
Crystals 2024, 14(7), 621; https://doi.org/10.3390/cryst14070621 - 5 Jul 2024
Viewed by 276
Abstract
S32750 dual-phase stainless steel (DSS) wires were prepared by cold drawing with a strain of ε = 0~3.6. The mechanical behavior and microstructural evolution of these DSS wires at different strains were investigated. Specifically, the yield strength and ultimate tensile strength of a [...] Read more.
S32750 dual-phase stainless steel (DSS) wires were prepared by cold drawing with a strain of ε = 0~3.6. The mechanical behavior and microstructural evolution of these DSS wires at different strains were investigated. Specifically, the yield strength and ultimate tensile strength of a S32750 DSS wire at a strain of ε = 3.6 reached 1771 MPa and 1952 MPa, respectively. The microstructure of the wire was transformed into a heterogeneous microstructure, which consisted of ferrite fiber grains and a nanofibrous grain structure consisting of austenite and strain-induced martensite nanofiber grains. A sub-grain structure was observed inside the ferrite fiber. The austenitic phase followed the evolutionary steps of stacking faults, twinning, ε-martensite, α-martensite, and, finally, austenite, before transitioning into a nanofibrous grain structure. This nanofibrous grain structure significantly contributed to the strength compared with the relatively coarse ferrite phase. Full article
(This article belongs to the Special Issue Dislocations and Twinning in Metals and Alloys)
9 pages, 2998 KiB  
Article
Synthesis, Crystal Structure, and Electropolymerization of 1,4-Di([2,2′-bithiophen]-3-yl)buta-1,3-diyne
by Alessandro Pedrini, Chiara Massera, Enrico Dalcanale, Marco Giannetto and Roberta Pinalli
Crystals 2024, 14(7), 620; https://doi.org/10.3390/cryst14070620 - 5 Jul 2024
Viewed by 525
Abstract
For their great structural versatility, thiophene-based π-conjugated systems have been widely exploited in the preparation of low band gap materials. Here, we report the synthesis of a highly conjugated tetrathiophene system, namely 1,4-di([2,2′-bithiophen]-3-yl)buta-1,3-diyne (1), that presents two bithiophene units connected at [...] Read more.
For their great structural versatility, thiophene-based π-conjugated systems have been widely exploited in the preparation of low band gap materials. Here, we report the synthesis of a highly conjugated tetrathiophene system, namely 1,4-di([2,2′-bithiophen]-3-yl)buta-1,3-diyne (1), that presents two bithiophene units connected at position 3 by a butadiynylene spacer. Single-crystal X-ray diffraction (SC-XRD) analysis elucidated the structure of 1, confirming the planarity of the molecule. The molecule was then electropolymerized onto the surface of a gold-coated piezoelectric quartz crystal, showing a high reactivity that is ascribable to the extended conjugation. The frontier molecular orbital energies of 1 were obtained via DFT optimization performed on the crystal structure-derived molecular geometry. Finally, DFT was also used to estimate the polymer band gap. Full article
Show Figures

Figure 1

14 pages, 17665 KiB  
Article
Enhancing the Predictive Modeling of n-Value Surfaces in Various High Temperature Superconducting Materials Using a Feed-Forward Deep Neural Network Technique
by Shahin Alipour Bonab, Wenjuan Song and Mohammad Yazdani-Asrami
Crystals 2024, 14(7), 619; https://doi.org/10.3390/cryst14070619 - 5 Jul 2024
Viewed by 277
Abstract
In this study, the prediction of n-value (index-value) surfaces—a key indicator of the field and temperature dependence of critical current density in superconductors—across various high-temperature superconducting materials is addressed using a deep learning modeling approach. As superconductors play a crucial role in [...] Read more.
In this study, the prediction of n-value (index-value) surfaces—a key indicator of the field and temperature dependence of critical current density in superconductors—across various high-temperature superconducting materials is addressed using a deep learning modeling approach. As superconductors play a crucial role in advanced technological applications in aerospace and fusion energy sectors, improving their performance model is essential for both practical and academic research purposes. The feed-forward deep learning network technique is employed for the predictive modeling of n-value surfaces, utilizing a comprehensive dataset that includes experimental data on material properties and operational conditions affecting superconductors’ behavior. The model demonstrates enhanced accuracy in predicting n-value surfaces when compared to traditional regression methods by a 99.62% goodness of fit to the experimental data for unseen data points. In this paper, we have demonstrated both the interpolation and extrapolation capabilities of our proposed DFFNN technique. This research advances intelligent modeling in the field of superconductivity and provides a foundation for further exploration into deep learning predictive models for different superconducting devices. Full article
(This article belongs to the Special Issue Superconductors and Magnetic Materials)
Show Figures

Figure 1

10 pages, 3664 KiB  
Article
Deposition and Structural Characterization of Mg-Zn Co-Doped GaN Films by Radio-Frequency Magnetron Sputtering in a N2-Ar2 Environment
by Erick Gastellóu, Rafael García, Ana M. Herrera, Antonio Ramos, Godofredo García, Gustavo A. Hirata, José A. Luna, Jorge A. Rodríguez, Mario Robles, Yani D. Ramírez and Iván E. García
Crystals 2024, 14(7), 618; https://doi.org/10.3390/cryst14070618 - 4 Jul 2024
Viewed by 327
Abstract
Mg-Zn co-doped GaN films were deposited by radio-frequency magnetron sputtering in an N2-Ar2 environment at room temperature, using a target prepared with Mg-Zn co-doped GaN powders. X-ray diffraction patterns showed broad peaks with an average crystal size of 13.65 nm [...] Read more.
Mg-Zn co-doped GaN films were deposited by radio-frequency magnetron sputtering in an N2-Ar2 environment at room temperature, using a target prepared with Mg-Zn co-doped GaN powders. X-ray diffraction patterns showed broad peaks with an average crystal size of 13.65 nm and lattice constants for a hexagonal structure of a = 3.1 Å and c = 5.1 Å. Scanning electron microscopy micrographs and atomic force microscopy images demonstrated homogeneity in the deposition of the films and good surface morphology with a mean roughness of 1.1 nm. Energy-dispersive spectroscopy and X-ray photoelectron spectroscopy characterizations showed the presence of gallium and nitrogen as elemental contributions as well as of zinc and magnesium as co-doping elements. Profilometry showed a value of 260.2 nm in thickness in the Mg-Zn co-doped GaN films. Finally, photoluminescence demonstrated fundamental energy emission located at 2.8 eV (430.5 nm), which might be related to the incorporation of magnesium and zinc atoms. Full article
Show Figures

Figure 1

Previous Issue
Back to TopTop