Crystals

16 pages, 10543 KiB

Open AccessArticle

Synthesis and Crystal Structure Analysis of Some Aromatic Imines of Syringaldehyde

by Christopher G. Hamaker and Stephan M. Germann

Crystals 2024, 14(1), 99; https://doi.org/10.3390/cryst14010099 - 22 Jan 2024

Cited by 1 | Viewed by 1601

A series of syringaldehyde imines with para-substituted anilines have been synthesized in a good yield, and their crystal structures have been analyzed. The orientation of the syringaldehyde hydroxyl group plays in important role in the intermolecular hydrogen-bonding pattern of the molecules. The [...] Read more.

A series of syringaldehyde imines with para-substituted anilines have been synthesized in a good yield, and their crystal structures have been analyzed. The orientation of the syringaldehyde hydroxyl group plays in important role in the intermolecular hydrogen-bonding pattern of the molecules. The O–H^…N hydrogen bonding interactions primarily determine the three-dimensional packing of the molecules, even though they make up a relatively small percentage of intermolecular interactions in the molecules. The three structures with the p-hydroxy group cis to the imine group give hydrogen-bonded zigzag chains in the monoclinic crystals, while the structure with a trans hydroxy group crystallize in a hexagonal space group (

R \bar{3}

) and form hydrogen-bonded hexamers. The hexagonal structure also displays Br^…Br interactions, forming additional hexameric clusters. The analysis of published p-hydroxyphenyl imine crystal structures from the Cambridge Crystallographic Database revealed patterns in the length of the hydrogen bonding interactions based on steric congestion around the hydroxyl group. Full article

(This article belongs to the Special Issue Different Kinds of Hydrogen Bonds in Crystal Structures)

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20 pages, 8966 KiB

Open AccessArticle

Investigating the Competitive Factors of Metal–Anion Coordination, Coordination by Water, and Hydrogen Bonding in Complexes of Cyanuric Acid with the Alkaline Earth Metals

by William Clegg and Gary S. Nichol

Crystals 2024, 14(1), 98; https://doi.org/10.3390/cryst14010098 - 22 Jan 2024

Cited by 2 | Viewed by 1548

Abstract

A survey of the trends in metal–ligand coordination and hydrogen bonding has been carried out on complexes of singly deprotonated cyanuric acid CY⁻ and alkaline earth metals, synthesised from aqueous solution and characterised by X-ray crystallography. The involvement of cyanurate in metal [...] Read more.

A survey of the trends in metal–ligand coordination and hydrogen bonding has been carried out on complexes of singly deprotonated cyanuric acid CY⁻ and alkaline earth metals, synthesised from aqueous solution and characterised by X-ray crystallography. The involvement of cyanurate in metal coordination increases from Mg through Ca and Sr to Ba relative to coordination by water, in parallel with increasing ionic radius and coordination number. The incidence of the bridging of metal centres by both water and cyanurate also increases in this series. The Mg complex [Mg(H₂O)₆][CY]₂·2H₂O contains hexaaqua-coordinated cations, uncoordinated CY⁻ anions, and additional water molecules. The Ca and Sr complexes {[Ca(CY)(H₂O)₃][CY]}_∞ and {[Sr(CY)₂(H₂O)₄]}_∞ feature polymeric chains of coordinated metal ions, the Ca complex with uncoordinated anions and the Sr complex with all potential ligands coordinated. The Ba complex {[Ba(CY)₂(H₂O)₂]}_∞ has a two-dimensional coordination network. Extensive hydrogen bonding plays a key role in generating a three-dimensional network in all four structures. The competition between cyanurate and water for coordination to the alkaline earth metal cations, and that between coordination and the hydrogen bonding propensities of the cyanurate anion, appear to be finely balanced, with the structural outcomes depending on the relative sizes and degrees of hardness of the four cations of the group. Full article

(This article belongs to the Section Crystal Engineering)

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12 pages, 8233 KiB

Open AccessArticle

The Effects of Indium Additions on Tribological Behavior of Spark Plasma Sintering-Produced Graphene-Doped Alumina Matrix Composites for Self-Lubricating Applications

by Viktor Puchý, Mária Podobová, Richard Sedlák, Ladislav Falat, Róbert Džunda, František Kromka and Ján Dusza

Crystals 2024, 14(1), 104; https://doi.org/10.3390/cryst14010104 - 22 Jan 2024

Cited by 1 | Viewed by 1248

Abstract

Alumina (Al₂O₃) ceramics are interesting for low-weight and mid-high temperature applications. The addition of indium (In) and graphene nanoplatelets (GNPs) can be used to reduce the density and modify the functional properties and mechanical performance of the ceramic matrix. [...] Read more.

Alumina (Al₂O₃) ceramics are interesting for low-weight and mid-high temperature applications. The addition of indium (In) and graphene nanoplatelets (GNPs) can be used to reduce the density and modify the functional properties and mechanical performance of the ceramic matrix. GNP and In-reinforced Al₂O₃ matrix composites were prepared by the spark plasma sintering (SPS) technique. Monolithic Al₂O₃ and Al₂O₃ matrix composites with either 5 or 10 wt.% of In and 2 wt.% of GNPs (Al₂O₃-5In-2GNPs and Al₂O₃-10In-2GNPs) were compacted into disc-shaped samples. The microstructure was studied and characterized with light-optical microscopy (LOM) and scanning electron microscopy (SEM). Hardness was determined using the Vickers technique and tribological properties were studied by the ball-on-disk method. The coefficient of friction (COF) and specific wear rates were evaluated from tribological tests. Worn surfaces were studied by SEM and confocal microscopy. Interdiffusion transition regions were formed among individual microstructural constituents (Al₂O₃, In, GNPs) under high sintering temperatures, which were responsible for the balanced hardness and low porosity of the produced composites. The addition of In and graphene nanoplatelets resulted in smaller COF and wear rates indicating good improvement in the tribological behavior. The prepared Al₂O₃-5In-2GNP and Al₂O₃-10In-2GNP composites represent promising nanocomposites for self-lubricating applications. Full article

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19 pages, 3173 KiB

Open AccessArticle

Microstructure and Properties Variation of High-Performance Grey Cast Iron via Small Boron Additions

by Grega Klančnik, Jaka Burja, Urška Klančnik, Barbara Šetina Batič, Luka Krajnc and Andrej Resnik

Crystals 2024, 14(1), 103; https://doi.org/10.3390/cryst14010103 - 22 Jan 2024

Viewed by 1593

Abstract

A study was undertaken to investigate the effects of small boron additions on the solidification and microstructure of hypo-eutectic alloyed grey cast iron. The characteristic temperatures upon crystallisation of the treated metal melt were recorded, specifically those concerning small boron addition by using [...] Read more.

A study was undertaken to investigate the effects of small boron additions on the solidification and microstructure of hypo-eutectic alloyed grey cast iron. The characteristic temperatures upon crystallisation of the treated metal melt were recorded, specifically those concerning small boron addition by using thermal analysis with the ATAS system. Additionally, a standardised wedge test was set to observe any changes in chill performance. The microstructures of thermal analysis samples were analysed using a light optical microscope (LOM) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS), which reveal variations in graphite count number with the addition of boron within observed random and undercooled flake graphite. The effect of boron was estimated by the classical analytical and statistical approach. The solidification behaviour under equilibrium conditions was predicted by a thermodynamic approach using Thermo-Calc. Based on all gathered data, a response model was set with boron for given melt quality and melt treatment using the experimentally determined data. The study reveals that boron as a ferrite and carbide-promoting element under the experimental set shows weak nucleation potential in synergy with other heterogenic nuclei at increased solidification rates, but no considerable changes were observed by the TA samples solidified at slower cooling rates, indicating the loss of the overall inoculation effect. The potential presence of boron nitride as an inoculator for graphite precipitation for a given melt composition and melt treatment was not confirmed in this study. It seems that boron at increased solidification rates can contribute to overall inoculation, but at slower cooling rates these effects are gradually lost. In the last solidification range, an increased boron content could have a carbide forming nature, as is usually expected. The study suggests that boron in traces could affect the microstructure and properties of hypo-eutectic alloyed grey cast iron. Full article

(This article belongs to the Topic Microstructure and Properties in Metals and Alloys, 2nd Volume)

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15 pages, 7354 KiB

Open AccessArticle

In-Gap Edge and Domain-Wall States in Largely Perturbed Phononic Su–Schrieffer–Heeger Lattices

by Amir Rajabpoor Alisepahi and Jihong Ma

Crystals 2024, 14(1), 102; https://doi.org/10.3390/cryst14010102 - 22 Jan 2024

Cited by 1 | Viewed by 1550

Abstract

Topological states of matter have attracted significant attention due to their intrinsic wave-guiding and localization capabilities robust against disorders and defects in electronic, photonic, and phononic systems. Despite the above topological features that phononic crystals share with their electronic and photonic counterparts, finite-frequency [...] Read more.

Topological states of matter have attracted significant attention due to their intrinsic wave-guiding and localization capabilities robust against disorders and defects in electronic, photonic, and phononic systems. Despite the above topological features that phononic crystals share with their electronic and photonic counterparts, finite-frequency topological states in phononic crystals may not always survive. In this work, we discuss the survivability of topological states in Su–Schrieffer–Heeger models with both local and non-local interactions and larger symmetry perturbation. Although such a discussion is still about ideal mass-spring models, the insights from this study set the expectations for continuum phononic crystals, which can further instruct the application of phononic crystals for practical purposes. Full article

(This article belongs to the Special Issue Metamaterials and Phononic Crystals)

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17 pages, 6503 KiB

Open AccessReview

A Critical Review of Anti-Corrosion Chemical Surface Treatment of Aluminum Alloys Used for Sports Equipment

by Bo Leng, Yuhua Xue, Jing Li, Jiantao Qi, Aihua Yi and Qixin Zhao

Crystals 2024, 14(1), 101; https://doi.org/10.3390/cryst14010101 - 22 Jan 2024

Cited by 3 | Viewed by 1685

Abstract

Aluminum alloys with low-weight property are promising structure materials for sports equipment. Alloying element-rich second-phase particles create the risk of localized corrosion and result in failure of sports equipment. Chromate conversion coatings as conventional and successful surface treatments were employed to provide a [...] Read more.

Aluminum alloys with low-weight property are promising structure materials for sports equipment. Alloying element-rich second-phase particles create the risk of localized corrosion and result in failure of sports equipment. Chromate conversion coatings as conventional and successful surface treatments were employed to provide a thin but compact film against corrosion. However, chromate species were toxic and carcinogenic for human beings and this process has been highly restricted. In this sense, alternative processes such as trivalent chromium conversion coating with low environmental risk require better corrosion-resistant performance compared to chromate conversion coating. In addition, the closed-loop system of the chromate electroplating process has been used in Europe and the United States. This is also a sustainable process for surface treatment of aluminum alloys applied in sports equipment. The present paper aims to summarize the methods and types of different aluminum alloy surface treatments and compiles the effects of various surface treatments on the corrosion resistance of aluminum alloys. The eco-friendly application of aluminum alloys in the field of sports equipment may be facilitated in the future. Full article

(This article belongs to the Special Issue Microstructure and Deformation of Advanced Alloys)

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24 pages, 6813 KiB

Open AccessArticle

Influence of Ultrahigh Dilution Treatment of the Charge on the Growth and Spectroscopic Properties of Nd:MgMoO₄ Potential Laser Crystal

by Kirill A. Subbotin, Yana S. Didenko, Anatolii I. Titov, Denis A. Lis, Sergei K. Pavlov, Pavel A. Volkov, Kristina I. Runina, Valerii V. Voronov, Elena V. Chernova, Olga N. Lis, Kristina V. Kuleshova and Yulia I. Zimina

Crystals 2024, 14(1), 100; https://doi.org/10.3390/cryst14010100 - 22 Jan 2024

Cited by 1 | Viewed by 1439

Abstract

The influence of the charge treatment by ultrahigh dilution (UHD) technology on oxide single crystals grown by the Czochralski technique was studied for monoclinic MgMoO₄ crystals doped by 1 at. % of Nd³⁺ ions. The series of 10 Nd:MgMoO₄ crystals [...] Read more.

The influence of the charge treatment by ultrahigh dilution (UHD) technology on oxide single crystals grown by the Czochralski technique was studied for monoclinic MgMoO₄ crystals doped by 1 at. % of Nd³⁺ ions. The series of 10 Nd:MgMoO₄ crystals was grown from the charges that were subjected to UHD treatment, as well as from the charges treated with two types of control or with no special treatment at all. The grown crystals were studied by X-ray powder diffraction analysis, inductively coupled plasma atomic emission spectroscopy, mass-spectrometry, optical absorption, emission spectroscopy and luminescence kinetic analysis. We found that: (i) wetting of MgO + MoO₃ mixture by a water-ethanol solution before calcining leads to some enrichment of the mixture with MoO₃, whereas the wetting of the charge after the calcining leads to some enrichment of it with MgO; (ii) congruent melting composition of MgMoO₄ crystal is in the field of some MoO₃ excess; (iii) the solid-phase solubility of the excess MoO₃ in MgMoO₄ probably does not depend on temperature, whereas the solid-phase solubility of the excess MgO in MgMoO₄ crystal depends on temperature. We suggest that the corresponding solidus line passes through the range of retrograde solubility; (iv) the crystals grown within this range are characterized by the enhanced Nd³⁺ segregation coefficient between the crystal and the melt (approximately 0.006 versus 0.004); (v) unit cell parameters of MgMoO₄ crystal with the excess of MoO₃ are larger than those of the crystal of the stoichiometric composition and of the crystal with the excess of MgO; (vi) the shapes of the optical absorption and luminescence spectra of Nd:MgMoO₄ crystal do not depend on the charge treatment; (vii) luminescence decay kinetics are single-exponential for all the studied crystals, the luminescence decay time being different for the crystals grown from the charges that underwent different types of treatment; (viii) the luminescence intensity of Nd:MgMoO₄ crystal grown from the charge that underwent UHD treatment before calcining (solid-phase synthesis) is reduced by an order of magnitude in comparison with the other studied crystals. Full article

(This article belongs to the Special Issue Raman Scattering in Optical Crystals (Volume II))

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34 pages, 22932 KiB

Open AccessReview

The Formation of Supramolecular Chiral Materials from Achiral Molecules Using a Liquid-Crystallin System: Symmetry Breaking, Amplification, and Transfer

by Atsushi Yoshizawa

Crystals 2024, 14(1), 97; https://doi.org/10.3390/cryst14010097 - 21 Jan 2024

Cited by 1 | Viewed by 3188

Abstract

Recently, the formation of chiral materials by the self-organization of achiral small molecules has attracted much attention. How can we obtain chirality without a chiral source? Interesting approaches, such as mechanical rotation, circularly polarized light, and asymmetric reaction fields, have been used. We [...] Read more.

Recently, the formation of chiral materials by the self-organization of achiral small molecules has attracted much attention. How can we obtain chirality without a chiral source? Interesting approaches, such as mechanical rotation, circularly polarized light, and asymmetric reaction fields, have been used. We describe recent research developments in supramolecular chirality in liquid crystals, focusing primarily on our group’s experimental results. We present the following concepts in this review. Spontaneous mirror symmetry breaking in self-assembled achiral trimers induces supramolecular chirality in the soft crystalline phase. Two kinds of domains with opposite handedness exist in non-equal populations. The dominant domain is amplified to produce a homochiral state. Chirality is transferred to a polymer film during the polymerization of achiral monomers by using the homochiral state as a template. Finally, we discuss how the concepts obtained from this liquid crystal research relate to the origin of homochirality in life. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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11 pages, 3606 KiB

Open AccessArticle

Toledoite, TiFeSi, a New Mineral from Inclusions in Corundum Xenocrysts from Mount Carmel, Israel

by Chi Ma, Fernando Cámara, Luca Bindi and William L. Griffin

Crystals 2024, 14(1), 96; https://doi.org/10.3390/cryst14010096 - 21 Jan 2024

Viewed by 1335

Abstract

During our nanomineralogical investigation of melt inclusions in corundum xenocrysts from the Mount Carmel area, Israel, seven new oxide and alloy minerals have been discovered since 2021. Herein, we report toledoite (TiFeSi; IMA 2022-036), a new alloy mineral. Toledoite occurs as irregular crystals [...] Read more.

During our nanomineralogical investigation of melt inclusions in corundum xenocrysts from the Mount Carmel area, Israel, seven new oxide and alloy minerals have been discovered since 2021. Herein, we report toledoite (TiFeSi; IMA 2022-036), a new alloy mineral. Toledoite occurs as irregular crystals 2–16 μm in size, with gupeiite (Fe₃Si), jingsuiite (TiB₂), ziroite (ZrO₂), osbornite (TiN), xifengite (Fe₅Si₃), and naquite (FeSi) in corundum Grain WG1124E-1. Toledoite has an empirical formula (Ti_0.83Cr_0.07Mn_0.06V_0.02)(Fe_0.96Mn_0.04)(Si_0.99P_0.04) and an orthorhombic Ima2 TiFeSi-type structure with the following cell parameters: a = 7.00(1) Å, b = 10.83(1) Å, c = 6.29(1) Å, V = 477(1) Å³, Z = 12. Toledoite is a high-temperature alloy phase, formed under extremely reduced conditions in melt pockets in corundum xenocrysts derived from the upper mantle beneath Mount Carmel in Israel. The name was given in honor of Vered Toledo, of Shefa Gems Ltd. for her support and for providing corundum xenocrysts from the Mount Carmel region for this investigation of new minerals. Full article

(This article belongs to the Special Issue The Progress of In-Situ Study of Mineralogy and Gemmology)

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11 pages, 1539 KiB

Open AccessArticle

The Universal Scaling of Dielectric Response as a Tool in the Description of a Complex Dynamic of 4′-Butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*)

by Marcin Piwowarczyk, Ewa Juszyńska-Gałązka and Mirosław Gałązka

Crystals 2024, 14(1), 95; https://doi.org/10.3390/cryst14010095 - 20 Jan 2024

Viewed by 1100

Abstract

The results of dielectric relaxation spectroscopy of the chiral liquid crystal 4′-butyl-4-(2-methylbutoxy)azoxybenzene in the crystal phase are presented. The scaling procedure showed complex molecular dynamics and allows one to decompose the observed relaxation process into two closely located relaxation processes around the short [...] Read more.

The results of dielectric relaxation spectroscopy of the chiral liquid crystal 4′-butyl-4-(2-methylbutoxy)azoxybenzene in the crystal phase are presented. The scaling procedure showed complex molecular dynamics and allows one to decompose the observed relaxation process into two closely located relaxation processes around the short molecular axis. Temperature dependences of relaxation times characterizing flip-flop motions (rotation around the short molecular axis) and rotation around the long molecular axis are of the Arrhenius type. Full article

(This article belongs to the Special Issue Liquid Crystal Phases and Phase Transitions)

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24 pages, 7446 KiB

Open AccessArticle

Controlling Crystal Growth of a Rare Earth Element Scandium Salt in Antisolvent Crystallization

by Josia Tonn, Andreas Roman Fuchs, Leon Libuda and Andreas Jupke

Crystals 2024, 14(1), 94; https://doi.org/10.3390/cryst14010094 - 19 Jan 2024

Viewed by 1617

Abstract

Recovering scandium from hydrometallurgical residue bears the potential of a better supply of an industry depending on imports from countries with more mineral resources than Europe. To recover scandium from unused metal production residue, strip liquors from a solvent extraction process are treated [...] Read more.

Recovering scandium from hydrometallurgical residue bears the potential of a better supply of an industry depending on imports from countries with more mineral resources than Europe. To recover scandium from unused metal production residue, strip liquors from a solvent extraction process are treated with an antisolvent to crystallize the ammonium scandium fluoride salt (NH₄)₃ScF₆ with high product yields. However, high local supersaturation leads to strong nucleation, resulting in small crystals, which are difficult to handle in the subsequent solid-liquid separation. Reducing local supersaturation makes it possible to reduce nucleation and control crystal growth. Key operation parameters are the concentration of ethanol in the feed and its addition rate. The concentration of the antisolvent in the feed causes a shorter mixing time in the proximity of the antisolvent inlet, which leads to a smaller local supersaturation and therefore less nucleation and more crystal growth. Lowering the antisolvent addition rate enhances this effect. The crystal size distribution during and at the end of the fed-batch process is analyzed by SEM imagery of sampled and dried crystals. To produce reproducible crystal size distribution from SEM images the neural network Mask R-CNN has been trained for the automated crystal detection and size analysis. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Second Edition)

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13 pages, 1060 KiB

Open AccessArticle

Asymptotic Solutions of Steady Lamellar Eutectic Growth in Directional Solidification for Small Tangent Values of the Contact Angles

by Jing Xiao and Xiangming Li

Crystals 2024, 14(1), 93; https://doi.org/10.3390/cryst14010093 - 19 Jan 2024

Viewed by 946

Abstract

A system of steady lamellar eutectic growth in directional solidification is considered with the case of small tangent values of the contact angles. The mathematical model is given in the non-dimensional rectangular coordinate system and the uniformly valid asymptotic solutions are obtained based [...] Read more.

A system of steady lamellar eutectic growth in directional solidification is considered with the case of small tangent values of the contact angles. The mathematical model is given in the non-dimensional rectangular coordinate system and the uniformly valid asymptotic solutions are obtained based on the method of the asymptotic expansions. The necessary condition for existing asymptotic solutions was obtained. The results indicate that the curvature undercooling and the solute undercooling determined the patterns of the solid–liquid interface. The dimensional average undercooling presents a relationship with eutectic spacing and pulling velocity. It can be seen that the dimensional average undercooling in front of both phases is not equal, and the total average undercooling as a function of the lamellar eutectic spacing exhibits a minimum. The minimum undercooling spacing decreases with an increase in the pulling velocity, which is in good agreement with Jackson and Hunt’s results. Full article

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13 pages, 1381 KiB

Open AccessArticle

Pseudo-Spin Polarized One-Way Elastic Wave Eigenstates in One-Dimensional Phononic Superlattices

by Pierre A. Deymier, Keith Runge, Alexander Khanikaev and Andrea Alù

Crystals 2024, 14(1), 92; https://doi.org/10.3390/cryst14010092 - 19 Jan 2024

Cited by 3 | Viewed by 1346

Abstract

We investigate a one-dimensional discrete binary elastic superlattice bridging continuous models of superlattices that showcase a one-way propagation character, as well as the discrete elastic Su–Schrieffer–Heeger model, which does not exhibit this character. By considering Bloch wave solutions of the superlattice wave equation, [...] Read more.

We investigate a one-dimensional discrete binary elastic superlattice bridging continuous models of superlattices that showcase a one-way propagation character, as well as the discrete elastic Su–Schrieffer–Heeger model, which does not exhibit this character. By considering Bloch wave solutions of the superlattice wave equation, we demonstrate conditions supporting elastic eigenmodes that do not satisfy the translational invariance of Bloch waves over the entire Brillouin zone, unless their amplitude vanishes for a certain wave number. These modes are characterized by a pseudo-spin and occur only on one side of the Brillouin zone for a given spin, leading to spin-selective one-way wave propagation. We demonstrate how these features result from the interplay of the translational invariance of Bloch waves, pseudo-spins, and a Fabry–Pérot resonance condition in the superlattice unit cell. Full article

(This article belongs to the Special Issue Advances and Application of Phononic Crystals)

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13 pages, 6214 KiB

Open AccessArticle

Piezoelectric Properties and Thermal Stability of Pb(Yb_1/2Nb_1/2)O₃-BiScO₃-PbTiO₃ Ternary Ceramics

by Fan Zhang, Hua Hao, Minghe Cao, Zhonghua Yao, Shuai Fu and Hanxing Liu

Crystals 2024, 14(1), 91; https://doi.org/10.3390/cryst14010091 - 19 Jan 2024

Cited by 1 | Viewed by 1101

Abstract

Piezoelectric ceramics with excellent piezoelectric properties and a high Curie temperature are important for numerous electromechanical devices in a broad range of temperature environments. In this work, the relaxor ferroelectric Pb(Yb_1/2Nb_1/2)O₃ end member was selected to be introduced [...] Read more.

Piezoelectric ceramics with excellent piezoelectric properties and a high Curie temperature are important for numerous electromechanical devices in a broad range of temperature environments. In this work, the relaxor ferroelectric Pb(Yb_1/2Nb_1/2)O₃ end member was selected to be introduced into a BiScO₃-PbTiO₃ high-temperature piezoelectric ceramic to reduce the dielectric loss and improve the piezoelectric properties while slightly reducing the Curie temperature. The phase structure and dielectric, ferroelectric and piezoelectric properties of 0.025Pb(Yb_1/2Nb_1/2)O₃-(0.975

-

x)BiScO₃-xPbTiO₃ (0.60 ≤ x ≤ 0.63) ceramics were systematically analyzed, and the best electrical properties were observed in the morphotropic phase boundary region x = 0.61 with d₃₃ = 370 pC/N, k_p = 44%, P_r = 33.9 μC/cm². Importantly, no significant depolarization was observed in the x = 0.61 ceramic from room temperature to 290 °C, demonstrating its good thermal stability and potential applications in a wide range of temperature environments. Full article

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14 pages, 5735 KiB

Open AccessArticle

Room-Temperature O₃ Detection: Zero-Bias Sensors Based on ZnO Thin Films

by Eleonora Bolli, Alice Fornari, Alessandro Bellucci, Matteo Mastellone, Veronica Valentini, Alessio Mezzi, Riccardo Polini, Antonio Santagata and Daniele Maria Trucchi

Crystals 2024, 14(1), 90; https://doi.org/10.3390/cryst14010090 - 18 Jan 2024

Cited by 3 | Viewed by 1414

Abstract

ZnO thin films with a thickness of 300 nm were deposited on Si and Al₂O₃ substrates using an electron beam evaporation technique with the aim of testing them as low cost and low power consumption gas sensors for ozone (O [...] Read more.

ZnO thin films with a thickness of 300 nm were deposited on Si and Al₂O₃ substrates using an electron beam evaporation technique with the aim of testing them as low cost and low power consumption gas sensors for ozone (O₃). Scanning electron microscopy and atomic force microscopy were used to characterize the film surface morphology and quantify the roughness and grain size, recognized as the primary parameters influencing the gas sensitivity due to their direct impact on the effective sensing area. The crystalline structure and elemental composition were studied through Raman spectroscopy and X-ray photoelectron spectroscopy. Gas tests were conducted at room temperature and zero-bias voltage to assess the sensitivity and response as a function of time of the films to O₃ pollutant. The results indicate that the films deposited on Al₂O₃ exhibit promising characteristics, such as high sensitivity and a very short response time (<2 s) to the gas concentration. Additionally, it was observed that the films display pronounced degradation effects after a significant exposure to O₃. Full article

(This article belongs to the Special Issue Advanced Surface Engineering Materials: Characterization and Properties)

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25 pages, 9798 KiB

Open AccessArticle

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

by Thomas Thuneman, Krishnan S. Raja and Indrajit Charit

Crystals 2024, 14(1), 89; https://doi.org/10.3390/cryst14010089 - 18 Jan 2024

Cited by 3 | Viewed by 1568

Abstract

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to [...] Read more.

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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17 pages, 3046 KiB

Open AccessArticle

Mammalian Cell Cytotoxicity, Antibacterial Activity and the Properties of Methylenebis(Hydroxybenzoic Acid) and Its Related Zinc(II) Complex

by Ayman H. Ahmed, Ibrahim O. Althobaiti, Marwah Aljohani, Ehab S. Gad, Yazeed M. Asiri and Omar A. Hussein

Crystals 2024, 14(1), 88; https://doi.org/10.3390/cryst14010088 - 17 Jan 2024

Viewed by 1516

Abstract

Formaldehyde, sulfuric acid and salicylic acid were combined to create a 3,3′-methylenebis(2-hydroxybenzoic acid) (MHB) ligand, which was subsequently permitted to bind with zinc(II) ions. The ligand and its zinc(II) complex (Zn–MHB) have been described by a combination of elemental analyses, spectral analyses (UV–Vis, [...] Read more.

Formaldehyde, sulfuric acid and salicylic acid were combined to create a 3,3′-methylenebis(2-hydroxybenzoic acid) (MHB) ligand, which was subsequently permitted to bind with zinc(II) ions. The ligand and its zinc(II) complex (Zn–MHB) have been described by a combination of elemental analyses, spectral analyses (UV–Vis, IR, MS and NMR), XRD, TEM, as well as TGA measurement. The ligand has been suggested to coordinate to the zinc center in a tetradentate manner forming the binuclear tetrahedral complex. An X-ray analysis indicated a considerable difference between MHB (crystalline) and Zn–MHB (amorphous). The UV–Vis spectra were used to determine the optical properties such as bandgap, refractive index, optical conductivity and penetration depth. The possibility of employing the samples for optoelectronic applications was indicated from the band gap values which underlie the range of semiconductors. TEM revealed the spherical shapes and mutation of ligand particles into the nano-scale by complexation. The antimicrobial potential of the MHB towards Gram-positive and Gram-negative bacterial growths has been investigated. The results suggested that it would be possible to employ MHB to prevent bacterial development, particularly that of salmonella typhimurium. The cytotoxicity of the MHB was assessed against two types of mammalian cells: VERO (the kidney of an African green monkey) and HFB4 (human skin melanocytes). Lower sensitivity was observed in VERO cells. Full article

(This article belongs to the Special Issue Coordination Complexes: Synthesis, Characterization and Application)

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14 pages, 8271 KiB

Open AccessArticle

Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6

by Hong-Zhi Hu, Yi-Bo Yan, Na Wang, Abuduheni Adila, Yang Liu and Zun-Qi Liu

Crystals 2024, 14(1), 87; https://doi.org/10.3390/cryst14010087 - 16 Jan 2024

Viewed by 1290

Abstract

The organic–inorganic hybrid compound, (o-BrAH)[H₂Co(CN)₆]_0.5·(18-crown-6)_0.5·H₂O, was synthesized and characterized by variable-temperature X-ray diffraction, single-crystal diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dielectric measurements. Single-crystal X-ray diffraction revealed [...] Read more.

The organic–inorganic hybrid compound, (o-BrAH)[H₂Co(CN)₆]_0.5·(18-crown-6)_0.5·H₂O, was synthesized and characterized by variable-temperature X-ray diffraction, single-crystal diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dielectric measurements. Single-crystal X-ray diffraction revealed a three-dimensional cage-like structure formed through the hydrogen bonds of cobalt hexacyanide, supermolecular cations, and water molecules. Temperature variation triggered an abrupt change in the cage structure and simultaneously caused dynamic oscillation of the supramolecules within the framework of [Co(CN)₆]₃⁻, inducing a phase transition accompanied by a step-like change in the dielectric physical properties. Full article

(This article belongs to the Section Crystal Engineering)

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26 pages, 5499 KiB

Open AccessReview

Lead-Free Double Perovskites: A Review of the Structural, Optoelectronic, Mechanical, and Thermoelectric Properties Derived from First-Principles Calculations, and Materials Design Applicable for Pedagogical Purposes

by David O. Obada, Shittu B. Akinpelu, Simeon A. Abolade, Emmanuel Okafor, Aniekan M. Ukpong, Syam Kumar R and Akinlolu Akande

Crystals 2024, 14(1), 86; https://doi.org/10.3390/cryst14010086 - 16 Jan 2024

Cited by 11 | Viewed by 4245

Abstract

Metal halide perovskite materials have shown significant advancements in their application as light absorbers in perovskite solar cells, with power conversion efficiencies reaching 27%. However, lead-based perovskites pose a concern due to their toxicity and stability issues in moisture, UV radiation, and heat. [...] Read more.

Metal halide perovskite materials have shown significant advancements in their application as light absorbers in perovskite solar cells, with power conversion efficiencies reaching 27%. However, lead-based perovskites pose a concern due to their toxicity and stability issues in moisture, UV radiation, and heat. This has led to a pressing need to explore substitute materials that do not contain lead but maintain the remarkable characteristics of lead-based perovskites. This review article focuses on halide double perovskites characterised by the A₂B’B”X₆ composition, highlighting their structural, optical, thermoelectric, and mechanical capabilities. Additionally, the review evaluates several materials databases to investigate materials suitable for high-throughput first-principles calculations integrated inside density functional theory. The review aims to identify novel perovskite materials, offer a thorough evaluation of the potential benefits and drawbacks associated with this class of materials, and, from the pedagogical standpoint, discover effective instructional frameworks. Full article

(This article belongs to the Special Issue Hydroxyapatite and Perovskite Materials: Synthesis, Characterization, Atomistic Simulations, and Resources for Teaching the Concepts)

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13 pages, 3228 KiB

Open AccessArticle

Refining Protein Envelopes with a Transition Region for Enhanced Direct Phasing in Protein Crystallography

by Ruijiang Fu, Wu-Pei Su and Hongxing He

Crystals 2024, 14(1), 85; https://doi.org/10.3390/cryst14010085 - 16 Jan 2024

Viewed by 1062

Abstract

In protein crystallography, the determination of an accurate protein envelope is of paramount importance for ab initio phasing of diffraction data. In our previous work, we introduced an approach to ascertain the protein envelope by seeking an optimal cutoff value on a weighted-average [...] Read more.

In protein crystallography, the determination of an accurate protein envelope is of paramount importance for ab initio phasing of diffraction data. In our previous work, we introduced an approach to ascertain the protein envelope by seeking an optimal cutoff value on a weighted-average density map. In this paper, we present a significant advancement in our approach by focusing on identifying a transition region that demarcates the boundary between the protein and solvent regions, rather than relying solely on a single cutoff value. Within this transition region, we conducted a meticulous search for the protein envelope using a finer map and our proposed transition hybrid input–output (THIO) algorithm. Through this improvement, we achieved a refined protein envelope even when starting from random phases, enabling us to determine protein structures with irregular envelopes and successfully phase crystals with reduced solvent contents. To validate the efficacy of our method, we conducted tests using real diffraction data from five protein crystals, each containing solvent contents ranging from 60% to 65%. Solving these structures through conventional direct methods proved difficult due to the limited solvent content. The mean phase error obtained through our proposed method was about 30°. The reconstructed model matched with the structure in the protein data bank with a root mean square deviation (r.m.s.d.) of about 1 Å. These results serve as compelling evidence that the utilization of the proposed transition region in conjunction with the THIO algorithm contributes significantly to the construction of a reliable protein envelope. This, in turn, becomes indispensable for the direct phasing of protein crystals with lower solvent contents. Full article

(This article belongs to the Special Issue Macromolecular Crystallography: Progress and Prospects)

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15 pages, 5666 KiB

Open AccessArticle

Inclusions and Spectral Characterization of Demantoid from Baluchistan, Pakistan

by Jian-Yi Zhang, Geng Li, Yu Tian and Fabian Schmitz

Crystals 2024, 14(1), 84; https://doi.org/10.3390/cryst14010084 - 16 Jan 2024

Cited by 7 | Viewed by 1436

Abstract

Demantoid is the green variety of andradite [Ca₃Fe₂(SiO₄)₃], an exceptionally rare and precious gemstone worldwide. In recent years, a small amount of gem-quality demantoid has been found in Pakistan. This research focuses on nine demantoids [...] Read more.

Demantoid is the green variety of andradite [Ca₃Fe₂(SiO₄)₃], an exceptionally rare and precious gemstone worldwide. In recent years, a small amount of gem-quality demantoid has been found in Pakistan. This research focuses on nine demantoids sourced from Muslim Bagh, Baluchistan, Pakistan, presenting a comprehensive analysis of the spectral characteristics and inclusions of Pakistani demantoid using classical gemological methods, energy dispersive X-ray fluorescence (EDXRF) chemical analyses, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and ultraviolet and visible (UV-vis) spectroscopy. The results show that the content of Cr and V in most samples is lower than the detection line of EDXRF, with only one sample containing a Cr₂O₃ content of 0.032%. The extremely low Cr content sets Pakistani demantoid apart from demantoid of the serpentinite type found in other regions. Notably, the UV-vis spectrum reveals characteristic absorption at 443 nm due to Fe³⁺, while a further contribution from Cr³⁺ would be highly likely, and weak absorption at 550 nm caused by Fe³⁺. This suggests that iron (Fe) is the primary chromogenic element of Pakistani demantoid, but the role of Cr³⁺ cannot be ignored. The FTIR spectrum of Pakistani demantoid displays the absorption peaks associated with [SiO₄]⁴⁻ groups at 937 cm⁻¹, 848 cm⁻¹, and 817 cm⁻¹, while the absorption peaks resulting from trivalent cations appear at 481 cm⁻¹ and 442 cm⁻¹, which are the characteristic FTIR spectra of demantoid. Raman spectroscopy further reveals absorption peaks are displayed near 994 cm⁻¹, 843 cm⁻¹, 818 cm⁻¹, associated with (Si–O)_Str vibrations (Si–O stretching vibration), and absorption peaks are displayed near 350 cm⁻¹ and 310 cm⁻¹, related to the rotation of SiO₄–R(SiO₄)⁴⁻, and the peaks near 514 cm⁻¹ and 494 cm⁻¹ are related to (Si–O)_bend vibrations (Si–O bending vibration). Additionally, related absorption peaks near 168 cm⁻¹ are attributed to the translation of SiO₄–T(SiO₄)⁴⁻, and absorption peaks near 234 cm⁻¹ are associated with the translation of X²⁺–T(X²⁺) (X²⁺ represents divalent ions). The common dark opaque inclusions found in Pakistani demantoid consist of a combination of magnetite and hematite. Additionally, some samples of Pakistani demantoid display inclusions of calcite. This unique combination of inclusions differentiates Pakistani demantoid from demantoids sourced from other regions. It signifies that Pakistani demantoid has a distinctive geological origin resulting from the interplay of serpentinization and skarnization processes. This geological formation distinguishes it from demantoids solely hosted in serpentinite or skarn environments in other origins. The identification of these characteristics holds significant importance for accurately determining the origin of Pakistani demantoid. Full article

(This article belongs to the Special Issue Gems Decoded: Bridging Gemology, Mineralogy, Crystallography and Geology)

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12 pages, 28607 KiB

Open AccessArticle

Microstructure and Mechanical Properties of TiC/WC-Reinforced AlCoCrFeNi High-Entropy Alloys Prepared by Laser Cladding

by Zhikai Zhu, Wenqing Shi and Jiang Huang

Crystals 2024, 14(1), 83; https://doi.org/10.3390/cryst14010083 - 15 Jan 2024

Viewed by 1330

Abstract

By employing the technology of laser cladding, AlCoCrFeNi–TiC_20−x/WC_x high-entropy alloy coatings (where x = 0, 5, 10, 15, and 20 is the mass fraction) were fabricated on 316L stainless steel (316Lss). The effects of changes in different mass fractions [...] Read more.

By employing the technology of laser cladding, AlCoCrFeNi–TiC_20−x/WC_x high-entropy alloy coatings (where x = 0, 5, 10, 15, and 20 is the mass fraction) were fabricated on 316L stainless steel (316Lss). The effects of changes in different mass fractions on the morphology, phase composition, microstructure, microhardness, and corrosion resistance of the composite coatings were studied. This demonstrates that the addition of TiC and WC powder produces an FCC phase in the original BCC phase, the morphology and size of the coatings from top to bottom undergo some changes with x, and the grain size evolution follows a cooling rate law. The evolution of microhardness and corrosion resistance of the coatings exhibit a trend of increasing first and then decreasing with an increase in x. The coatings exhibited their best microhardness and corrosion resistance when x = 15, and their corrosion resistance and microhardness were much better than those of the substrate. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) for Advanced Materials and Structures: Green and Intelligent Development Trend Volume II)

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15 pages, 6577 KiB

Open AccessArticle

Synthesis and Characterization of Indium-Doped SnO₂-Based Impedance Spectroscopy Sensor for Real-Time Humidity Sensing Applications

by Birhanu Alemayehu, Eunsung Shin, Vladimir Vasilyev and Guru Subramanyam

Crystals 2024, 14(1), 82; https://doi.org/10.3390/cryst14010082 - 15 Jan 2024

Cited by 1 | Viewed by 1393

Abstract

Metallic transition-metal dichalcogenides are emerging as promising electrode materials for applications such as 2D electronic devices owing to their good electrical conductivity. In this study, a high-performance humidity sensor based on NbTe₂ electrode material and an indium-doped SnO₂ thin film sensing [...] Read more.

Metallic transition-metal dichalcogenides are emerging as promising electrode materials for applications such as 2D electronic devices owing to their good electrical conductivity. In this study, a high-performance humidity sensor based on NbTe₂ electrode material and an indium-doped SnO₂ thin film sensing layer was fabricated using a pulsed laser deposition system. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized. Additionally, the humidity sensing response of the fabricated sensor with In-doped SnO₂ (8:92 wt%) sensing film was evaluated in a wide range of relative humidity at room temperature. The results demonstrated that the humidity sensor based on In-doped SnO₂ exhibited a high sensitivity of 103.1 Ω/%RH, fast response and recovery times, a low hysteresis value, good linearity, and repeatability. In addition, the sensor had good long-term stability, with a variation in impedance of less than 3%. The results indicated that the humidity sensor could be suitable for practical humidity sensing applications. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 7332 KiB

Open AccessArticle

Microstructural and Hall–Petch Analysis of Additively Manufactured Ferritic Alloy Using 2507 Duplex Stainless Steel Powder

by Mustafa Tobah, Mohsen T. Andani, Bibhu P. Sahu and Amit Misra

Crystals 2024, 14(1), 81; https://doi.org/10.3390/cryst14010081 - 15 Jan 2024

Cited by 4 | Viewed by 3535

Abstract

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 [...] Read more.

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 alloy was nearly 100% ferrite. Optimal processing conditions that minimized porosity were determined to be 290 W laser power and 1000 mm/s scan speed, and grain size, texture, and phases were characterized as a function of laser power and scan speed. Grain size increased with increasing laser power but decreased with increasing scan speed. A <100> texture diminished with increasing scan speed from 1000 mm/s to 1400 mm/s. No austenite phase was detected. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization revealed nanoscale chromium nitride precipitates in the ferritic matrix (incoherent hexagonal close-packed (HCP) precipitates at grain boundaries and coherent body-centered cubic (BCC) precipitates within the grains) and a high density of tangled dislocations. Tensile tests of as-printed alloys showed a yield strength of 570 MPa, an ultimate tensile strength of 756 MPa, and an elongation to failure of 10%. The tensile properties were analyzed based on the observed microstructure considering grain size, nanoscale precipitates, and the high density of dislocations. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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22 pages, 8868 KiB

Open AccessArticle

Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

by Yu Yuan, Zhuang Miao, Yi Zhao, Bo Xu, Jialu Gu and Pengyu Yuan

Crystals 2024, 14(1), 80; https://doi.org/10.3390/cryst14010080 - 14 Jan 2024

Viewed by 1741

Abstract

Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central [...] Read more.

Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central High Atlas were investigated through gemological and chemical studies, including infrared spectrum, Raman spectrum, SEM-EDS, and LA-ICP-MS. Two titanite samples are yellow, transparent–translucent with a greasy luster, 3.5 and 2.5 mm long. MA-1 and MA-2 have similar gemological properties, the refractive index (RI) is beyond the range of the refractometer (>1.78), the specific gravity (SG) values fall in the range of 3.52~3.54 and both are inert to short-wave and long-wave UV radiation. The spectral characteristics have high consistency with the RRUFF database. The major elements’ composition shows a negative correlation between Al, Fe, V, and Ti, suggesting the titanites underwent substitutions such as (Al, Fe³⁺) + (F, OH) ↔ Ti + O. The titanite samples, characterized by a low abundance of REE (802~4088 ppm) and enriched in LREE, exhibit positive Eu (δEu: 1.53~7.79) and Ce (δCe: 1.08~1.33) anomalies, indicating their formation in a hydrothermal environment with low oxygen fugacity. The ²³⁸U/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb ratios of the titanites yield lower intercept ages of 152.6 ± 2.2 and 151.4 ± 5.3 Ma (1s), consistent with their weighted average ²⁰⁶Pb/²³⁸U ages of 152.3 ± 2.0 and 150.7 ± 3.2 Ma (1s) respectively. The results of U-Pb dating are matched with the second main magmatic activities in the High Atlas intracontinental belt of Morocco during the Mesozoic to Cenozoic period. Moreover, the two titanite samples have almost no radiational damage. All the results show that the titanite from High Atlas, Morocco, has the potential to be a reference material for LA-ICP-MS U–Pb dating, but further experiments are needed to be sure. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

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13 pages, 4301 KiB

Open AccessArticle

A Self-Powered Broadband Photodetector with High Photocurrent Based on Ferroelectric Thin Film Using Energy Band Structure Design

by Xing Gao, Xin Song, Shan Zhang, Xinxiang Yang, Pei Han, Liwen Zhang, Chunxiao Lu, Xihong Hao and Yong Li

Crystals 2024, 14(1), 79; https://doi.org/10.3390/cryst14010079 - 13 Jan 2024

Cited by 1 | Viewed by 1523

Abstract

Self-powered photodetectors have the advantages of high sensitivity, sustainability, and small size and have become a research hotspot in advanced optoelectronic systems. However, the low output photocurrent density seriously hinders the practical application of ferroelectric self-powered photodetectors. Herein, the high-efficiency photoelectric detection performance [...] Read more.

Self-powered photodetectors have the advantages of high sensitivity, sustainability, and small size and have become a research hotspot in advanced optoelectronic systems. However, the low output photocurrent density seriously hinders the practical application of ferroelectric self-powered photodetectors. Herein, the high-efficiency photoelectric detection performance of the Bi_1-xHo_xFeO₃ ferroelectric self-powered photodetector is realized by doping Ho. The responsivity (R) and detectivity (

D^{*}

) can reach 0.0159 A/W and 1.94 × 10¹¹ Jones under monochromatic light with a wavelength of 900 nm. Meanwhile, the R and

D^{*}

can reach 0.022 A/W and 2.65 × 10¹¹ Jones under sunlight. These excellent photodetection performances are attributed to the high short-circuit current density (J_sc). When the Ho content is 6%, the output photocurrent reaches up to 0.81 mA/cm². The systematic structure and photo-electric characteristic analysis suggest that the decrease in the band gap leads to the generation of a larger photocurrent while the ferroelectric polarization is reduced slightly. This work provides a new way to obtain high-performance self-powered photodetectors. Full article

(This article belongs to the Special Issue Ferroelectric and Multiferroic Thin Films)

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14 pages, 12717 KiB

Open AccessArticle

Analysis of the Effect of Copper Doping on the Optoelectronic Properties of Indium Oxide Thin Films and the Thermoelectric Properties of an In₂O₃/Pt Thermocouple

by Yantao Liu, Tao Lin, Rong Huang, Jiahao Shi and Sui Chen

Crystals 2024, 14(1), 78; https://doi.org/10.3390/cryst14010078 - 13 Jan 2024

Cited by 2 | Viewed by 1581

Abstract

The detection and real-time monitoring of temperature parameters are important, and indium oxide-based thin film thermocouples can be integrated on the surface of heaters because they operate normally under harsh conditions and provide accurate online temperature monitoring. The higher stability and appropriate optical [...] Read more.

The detection and real-time monitoring of temperature parameters are important, and indium oxide-based thin film thermocouples can be integrated on the surface of heaters because they operate normally under harsh conditions and provide accurate online temperature monitoring. The higher stability and appropriate optical and electrical properties of In₂O₃ make it very suitable as an electrode material for thermocouple sensors. This work demonstrates that copper doping can alter the optical and electrical properties of In₂O₃ films and regulate the output performance of thermocouples. Copper-doped In₂O₃ thin films were prepared using the magnetron co-sputtering method. The doping concentration of Cu was controlled using direct current (DC) power. An In₂O₃/Pt thermocouple sensor was prepared, and the optoelectronic and thermocouple properties were adjusted by changing the copper doping content. The thickness valve of the thin film sample was 300 nm. The results of the X-ray diffraction suggested that the structure of the doped In₂O₃ thin films was cubic. The results of the energy-dispersive X-ray analysis revealed that Cu was doped into the In₂O₃ thin films. All deposited films were n-type semiconductor materials according to Hall effect testing. The 4.09 at% Cu-doped thin films possessed the highest resistivity (30.2 × 10⁻³ Ω·cm), a larger carrier concentration (3.72 × 10²⁰ cm⁻³), and the lowest carrier mobility (0.56 cm²V⁻¹s⁻¹). The optical band gap decreased from 3.76 to 2.71 eV with an increase in the doping concentration, and the transmittance of the film significantly reduced. When the DC power was increased, the variation range of Seebeck coefficient for the In₂O₃/Pt thermocouple was 152.1–170.5 μV/°C, and the range of thermal output value was 91.4–102.4 mV. Full article

(This article belongs to the Special Issue Wide-Bandgap Semiconductor Materials, Devices and Systems)

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26 pages, 4510 KiB

Open AccessEditor’s ChoiceReview

Crystal Engineering of Hydrogen Bonding for Direct Air Capture of CO₂: A Quantum Crystallography Perspective

by Sylwia Pawlędzio and Xiaoping Wang

Crystals 2024, 14(1), 77; https://doi.org/10.3390/cryst14010077 - 13 Jan 2024

Cited by 2 | Viewed by 2161

Abstract

Rising atmospheric CO₂ levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum [...] Read more.

Rising atmospheric CO₂ levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum crystallography techniques and computational modeling, to unlock the full potential of DAC materials. We examine the critical role of hydrogen bonding and other noncovalent interactions within a family of bis-guanidines that governs the formation of carbonate salts with high CO₂ capture capacity and low regeneration energies for utilization. Quantum crystallography and charge density analysis prove instrumental in elucidating these interactions. A case study of a highly insoluble carbonate salt of a 2,6-pyridine-bis-(iminoguanidine) exemplifies the effectiveness of these approaches. However, challenges remain in the systematic and precise determination of hydrogen atom positions and atomic displacement parameters within DAC materials using quantum crystallography, and limitations persist in the accuracy of current energy estimation models for hydrogen bonding interactions. Future directions lie in exploring diverse functional groups, designing advanced hydrogen-bonded frameworks, and seamlessly integrating experimental and computational modeling with machine learning. This synergistic approach promises to propel the design and optimization of DAC materials, paving the way for a more sustainable future. Full article

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17 pages, 4883 KiB

Open AccessArticle

Cobalt(II) Paddle-Wheel Complex with 3,5-Di(tert-butyl)-4-hydroxybenzoate Bridges: DFT and ab initio Calculations, Magnetic Dilution, and Magnetic Properties

by Tatiana V. Astaf’eva, Stanislav A. Nikolaevskii, Evgeniy N. Egorov, Stanislav N. Melnikov, Dmitriy S. Yambulatov, Anna K. Matiukhina, Marina E. Nikiforova, Maxim A. Shmelev, Aleksandr V. Kolchin, Nikolay N. Efimov, Sergey L. Veber, Artem S. Bogomyakov, Ekaterina N. Zorina-Tikhonova, Igor L. Eremenko and Mikhail A. Kiskin

Crystals 2024, 14(1), 76; https://doi.org/10.3390/cryst14010076 - 13 Jan 2024

Viewed by 1608

Abstract

A new binuclear "paddle-wheel" complex, [Co₂(bhbz)₄(EtOH)₂]·4EtOH (1, Hbhbz-3,5-di(tert-butyl)-4-hydroxybenzoic acid); an isostructural zinc complex (2); a and magnetically diluted sample of [Zn_1.93Co_0.07(bhbz)₄(EtOH)₂]·4EtOH (3 [...] Read more.

A new binuclear "paddle-wheel" complex, [Co₂(bhbz)₄(EtOH)₂]·4EtOH (1, Hbhbz-3,5-di(tert-butyl)-4-hydroxybenzoic acid); an isostructural zinc complex (2); a and magnetically diluted sample of [Zn_1.93Co_0.07(bhbz)₄(EtOH)₂]·4EtOH (3) were obtained. Molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. DFT calculations for 1 indicate strong Co-Co antiferromagnetic exchange interactions in the binuclear fragment. It was shown that when one paramagnetic ion in the binuclear molecule is replaced by a diamagnetic zinc(II) ion, the remaining cobalt(II) ion can be considered as an isolated center with magnetic anisotropy, the parameters of which are determined by ab initio calculations. Magnetic properties for samples 1 and 3 were investigated and analyzed in detail. Full article

(This article belongs to the Special Issue Fabrication and Properties of Magnetic Materials)

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12 pages, 4325 KiB

Open AccessArticle

Hot-Electron Microwave Noise and Energy Relaxation in (Be)MgZnO/ZnO Heterostructures

by Emilis Šermukšnis, Artūr Šimukovič, Vitaliy Avrutin, Natalia Izyumskaya, Ümit Özgür and Hadis Morkoç

Crystals 2024, 14(1), 75; https://doi.org/10.3390/cryst14010075 - 12 Jan 2024

Viewed by 1202

Abstract

Pulsed hot-electron microwave noise measurements of the (Be)MgZnO/ZnO heterostructures are presented in this work. The heterostructures of different barrier thicknesses and different bulk electron densities in ZnO layer are compared. Capacitance–voltage (C–V) measurements reveal the decrease in the two-dimensional electron gas (2DEG) peak [...] Read more.

Pulsed hot-electron microwave noise measurements of the (Be)MgZnO/ZnO heterostructures are presented in this work. The heterostructures of different barrier thicknesses and different bulk electron densities in ZnO layer are compared. Capacitance–voltage (C–V) measurements reveal the decrease in the two-dimensional electron gas (2DEG) peak in electron density profile at the Zn-polar BeMgZnO/ZnO interface as the BeMgZnO barrier layer thickness decreases. For thin-barrier heterostructures, the peak disappears and only the bulk electron density is resolved in C–V measurements. The excess noise temperature at ∼10 GHz in thick-barrier heterostructures is noticeably higher (∼10 times) compared to thin-barrier heterostructures, which is attributed to the strong noise source in the contacts of the former. In the case of thin-barrier heterostructures, at electric fields above ∼10 kV/cm and electron density

≳ 1 \times 10^{17} {cm}^{- 3}

, strong noise source is resolved, which was also observed earlier in the Ga-doped ZnO films due to the formation of self-supporting high-field domains. However, for the low electron densities (≲6

\times 10^{16}

cm

^{- 3}

), the aforementioned noise source is not observed, which suggests the importance of a deep ZnO/GaN interface with 2DEG for power dissipation. The hot-electron temperature dependence on the dissipated power of those low-electron-density heterostructures is similar to that of O-polar ZnO/MgZnO. The estimated electron energy relaxation time in ZnO/MgZnO is ∼0.45 ps ± 0.05 ps at dissipated electrical power per electron of ∼0.1 nW/el and approaches ∼0.1 ps as the dissipated power is increased above ∼10 nW/el. Full article

(This article belongs to the Section Crystal Engineering)

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