Body-centered Tetragonal Structure Research Articles

Strain-Assisted Phase Transformation in Two-Dimensional Transition-Metal Dichalcogenides.

Two-dimensional polymorphic transition-metal dichalcogenides have drawn attention for their diverse applications. This work explores the complex interplay between strain-induced phase transformation and crack growth behavior in annealed nanocrystalline MoS2. Employing molecular dynamics (MD) simulations, this research focuses on the effect of grain size, misorientation, and annealing on phase evolution and their effects on the mechanical behavior of MoS2. First, examining phase transformation in monocrystalline MoS2 under various stress states reveals distinct behaviors depending on the initial phase (1T or 2H) and crystallographic orientation with respect to loading directions. Notably, transformation from a layered hexagonal to a body-centered tetragonal structure is more noticeable when strain in a zigzag direction is applied to the 1T sample. As such, single crystalline MoS2 with a 1T phase exhibits a 16% lower fracture stress in the armchair direction compared to that with a 2H phase. On the other hand, the 1T phase shows a 5% higher phonon lifetime compared to the 2H phase with similar phonon group velocities. Next, the influence of thermal energy and mechanical stress on the phase transformation of nanocrystalline MoS2 is investigated through annealing and quenching cycles, uncovering 60 and 44% irreversibility of phase transformation for an average grain size of 3 and 11 nm, respectively. Besides, the evolution of nanocrystalline samples with different initial phases and grain sizes is studied under uniaxial and biaxial stress. This study shows an inverse pseudo-Hall-Petch effect with exponents of 0.11 and 0.09 for 2H and 1T, respectively. The study reveals that phase transformation can occur concurrently with crack initiation and propagation with the 1T phase exhibiting a 19% lower grain size sensitivity of fracture stress compared to the 2H phase.

The effect of f-electrons on the structural phase transition, mechanical and electronic properties in light rare-earth bismuthides

ABSTRACT The electronic structure, phase transition pressure and mechanical properties of light rare-earth bismuthides (PrBi, NdBi, PmBi and SmBi) have been investigated by full geometry optimization using Vienna Ab-Initio Simulation Package (VASP) which has been used in combination with the projector augmented wave (PAW) method and the generalized gradient approximation (GGA) over the local density approximation (LDA) for exchange-correlation functional. We focus our attention on the lattice constants and elastic constants of these compounds. These compounds undergo a phase transition from the NaCl (B1) structure to the body-centered tetragonal (BCT) structure. We also report the density of states (DOS) of these rare earth bismuthides. In the case of PrBi and NdBi, the 4f states are treated as valence states. The effects of on-site Coulomb repulsion and the spin-orbit coupling (SOC) on the electronic structure are also studied.

Effects of ultrasonic cavitation on microstructure and surface properties of Mn–Cu alloy

In the presented study, the effects of ultrasonic vibration on microstructure and surface properties of Mn–Cu alloy were investigated. At the early stage of ultrasonic cavitation treatment, grains of Mn–Cu alloy are refined, nanocrystals and amorphous bands are produced. As the ultrasonic cavitation treatment proceeds, the face-centered cubic structure is transformed into the body-centered tetragonal structure, and the martensitic phase transformation arises. The transformation is accompanied by plastic deformation and the formation of dislocations. The generation of martensite is caused by the stress and strain. Due to grain refinement, dislocations, and generation of martensite, the surface hardness of Mn–Cu alloy is enhanced, and the friction coefficient decreases. The resistance to wear is thereby improved.

Fluoromethane and chloromethane adsorption studies on hydrogenated C8 nanosheets – A first-principles study

We studied the structural stability of hydrogenated C8 (H-C8) sheets which exhibit body-centered tetragonal (BCT) structure and found to be stable in its structure. The energy gap of H-C8 sheets is observed to be 3.517 eV. The structural firmness of H-C8 is verified with formation energy, which is recorded as −5.947 eV/atom. Besides, fluoromethane and chloromethane, two predominant halomethanes are adsorbed on H-C8 nanosheets. The effectiveness of the H-C8 sheets for the detection of fluoromethane and chloromethane is explored in the current work with the help of density functional theory (DFT) calculations. In addition, the electronic properties and adsorption attributes of fluoromethane and chloromethane on H-C8 sheets were investigated through the band structure, DOS spectrum, and electron density difference diagrams. Moreover, the charge transfer and adsorption energy calculations were also determined to ascertain halomethane adsorption. The results show that halomethanes are physisorbed (-0.429 eV to −0.823 eV) as well as chemisorbed (-1.574 eV) on H-C8 sheets. Thus, H-C8 nanosheets can be used as a sensing element towards fluoromethane and chloromethane molecules.

Formation of a Body-Centered Tetragonal Structure With High Magnetic Anisotropy and Coercivity in Fe–Co–V Films With High C Contents

A high amount of C (0–20 at.%) was added to Fe–Co–V films via sputtering to transform their body-centered cubic (bcc) structure to a face-centered cubic (fcc) lattice through a body-centered tetragonal (bct) structure. The Fe–Co films without V retained a bcc or bct crystal structure with an axial ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c/a</i> ) of 1.03 even at high C contents close to 20 at.%. Meanwhile, in the Fe–Co films containing 10 at.% of V, a bct structure with 1.06 ≤ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c/a</i> ≤ 1.30 was formed after adding 5–12 at.% of C, which was subsequently transformed to an fcc structure with increasing C content. The saturation magnetization of the Fe–Co–V–C films with the bct structure was approximately 1000–1500 kA/m, and their uniaxial magnetic anisotropy constant ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ) was approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (the films with high Fe contents exhibited high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> values). The bct Fe–Co–V–C films with high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> were microfabricated into nanodot array patterns via electron beam lithography. The coercivity of the pattern increased with decreasing dot size, and that of the pattern with a dot diameter of 85 nm was nearly an order of magnitude higher than that of the continuous film.

Unraveling the Atomic Shuffles of Twinning Nucleation in Hexagonal Close-Packed Rhenium Nanocrystals.

Reining in deformation twinning is crucial for the mechanical properties of hexagonal close-packed (HCP) metals and hinges on an explicit understanding of the twinning nucleation mechanism. Unfortunately, it is often suggested rather than conclusively demonstrated that twinning nucleation can be mediated by pure atomic shuffles. Herein, by utilizing in situ high-resolution transmission electron microscopy, we have dissected the atomic shuffling mechanism during the {101̅2} twinning nucleation in rhenium nanocrystals, which revealed the emergence of an intermediate body-centered tetragonal (BCT) structure. Specifically, the double-layered prismatic planes initially shuffle into single-layered {11̅0}BCT planes; subsequently, adjacent {22̅0}BCT planes shuffle in opposite directions to form the basal planes of the twin embryo. This shuffling mechanism is further corroborated by molecular dynamic simulations. The finding provides direct evidence of shuffle-dominated twinning nucleation with atomic details that may lead to better control of this critical twinning mode in HCP metals.

High Capacity Sn Metal Anode for Aqueous Proton-Based Batteries

Aqueous proton-based batteries (APBs) as a good choice to respond battery diversity, delivering safety, cost, environmental friendliness and high-power necessary for renewable energy storage.1 However, most promising conventional aqueous battery anodes have relatively poor compatibility in acid. The limited existing anode options like Pb and MoO3 can hardly match the high-performance of advanced cathodes, leading low-voltage and unsatisfactory energy density of APBs.2-4 Therefore, the exploration of high-performance anode materials is thus of critical issue for the APB assembling.Sn metal should be one of the most suitable APB anode choices due to its relatively high hydrogen evolution reaction (HER) overpotential, large theoretical capacity (451.6 mAh g−1) and negative redox potential (−0.14 V vs. SHE). With a body-centered tetragonal crystal structure and similar facet surface energy, Sn metal deposit in polyhedral morphology isotropically. This may cause serious “dead Sn” issue when deposition capacity increases because large Sn particle has limited contact with the substrate and easily to shed from the electrode, resulting in low Coulombic efficiency and short lifespan.We will present our efforts of developing Sn anode with high capacity and long lifespan by an interfacial alloying regulation approach. Smaller grain size and more uniform Sn deposition can be achieved by higher propensity for nucleation and Sn migration energy barrier. Extra interfacial interaction suppresses shedding of Sn polyhedron particles, thus prohibiting the formation of “dead” Sn. Based on the optimized Sn metal anode, we propose several promising designs for APBs, with high performance such as high output voltages, good specific energy densities, fast kinetics, and long life. References X. Wu, J. J. Hong, W. Shin, L. Ma, T. Liu, X. Bi, Y. Yuan, Y. Qi, T. W. Surta, W. Huang, J. Neuefeind, T. Wu, P. A. Greaney, J. Lu, X. Ji. Nat. Energy 2019, 4, 123-130.W. Chen, G. Li, A. Pei, Y. Li, L. Liao, H. Wang, J. Wan, Z. Liang, G. Chen, H. Zhang, J. Wang, Y. Cui. Nat. Energy 2018, 3, 428-435.Y. Liang, Y. Jing, S. Gheytani, K. Y. Lee, P. Liu, A. Facchetti, Y. Yao. Nat. Mater. 2017, 16, 841-848.X. Wang, Y. Xie, K. Tang, C. Wang, C. Yan. Angew. Chem. Int. Ed. 2018, 57, 11569-11573.

The structural diversity and properties of NbxMo1-xO2

We synthesized NbxMo1-xO2 series compounds and determined the structure of each component through x-ray diffraction and selected area electron diffraction techniques. For x=0.05, 0.1, 0.2, they possess room temperature MoO2 monoclinic structure (P21/c); for x=0.25, 0.3, they become to body-centered tetragonal structure (I41/a); for x=0.33, 0.6, 0.65, they further turn to TiO2 rutile-type structure (P42/mnm). Nb0.25Mo0.75O2 has transport and magnetic properties similar to those of NbMoO4 as paramagnetic metal. Moreover, the UV–vis spectra indicate the metallic property of Nb0.05Mo0.95O2, Nb0.25Mo0.75O2, and Nb0.6Mo0.4O2. X-ray absorption spectra at the Mo-L3 and Nb-L3 edges present Mo4+/Nb4+ and Mo4+/Nb5+ valence state for Nb0.25Mo0.75O2 and Nb0.05Mo0.95O2, respectively. This means the latter can be descripted as Nb0.05Mo0.95O2+δ with δ = 0.025.

Constituent phases, microstructures, and martensitic transformation of β-type Zr-Nb-Sn alloys

Constituent phases, shape memory and superelastic properties and microstructure in β-type Zr–(6–10.5)Nb–(2–5)Sn (at.%) alloys were investigated. Zr–(8–10.5)Nb–(2–4)Sn alloys exhibited shape memory effect and partial superelastic recovery. Zr–(8–9)Nb–5Sn alloys exhibited distinct superelasticity. The alloys with low Nb content (x < 8 at.%) exhibited an α” phase and a β phase. For the alloys with high Nb content (x ≥ 8 at.%), in addition to the matrix of a β phase, a β′ phase with a body-centered tetragonal structure was observed. Lattice deformation strains were calculated based on the lattice parameters of the β phase and the α” phase. The distribution of the β′ phase showed no significant Nb content dependence, whereas the addition of Sn caused a sparse distribution of the β′ phase. In situ X-ray diffraction measurements under heating and cooling revealed that transformation between the β phase and the β′ phase is reversible. The β′ phase was absent in the deformation-induced α” phase, suggesting that β’→α” phase transformation occurred during the deformation together with β → α” phase transformation. TEM observation revealed that dislocations remained in the deformation-induced α” phase closed to the β′ phase. The presence of the β′ phase was considered to be the cause for a larger stress hysteresis and a smaller superelastic recovery strain in the Zr-based superelastic alloys than those in Ti-based superelastic alloys. The effect of the β’ phase on the superelastic properties of Zr-based alloys was discussed in comparison with Ti-based alloys.

A first-principles study on the early-stage corrosion of a NiWNb alloy in a chloride salt environment

In this work a representative nickel superalloy, Ni70W20Nb10, was investigated in the presence of chlorine to quantify its early-stage dissolution behavior. Surface structures were generated from a bulk configuration sampled in equilibrium using a multi-cell Monte Carlo method for phase prediction. The predicted solid-phase at 800∘C was Ni72W19Nb9 in a body-centered tetragonal crystal structure closely resembling the Ni4W structure. Chlorine adsorption onto the energetically favored (110) surface showed preference to niobium which acted as a trapping sink on the top surface of the slab model. Our findings suggested that niobium and tungsten enhanced the corrosion resistance of nickel as their presence created regions that were thermodynamically preferred by the incoming chlorine and less susceptible to chlorine-facilitated dissolution from the alloy. Nickel, niobium, and tungsten resisted chlorine-induced dissolution from the surface model up to a 1/3 monolayer coverage of chlorine indicating that all constituents of this alloy possessed superior resistance to localized surface degradation such as corrosive pitting. Further analysis and comparisons between the corrosion resistance of the three metallic species was performed. This work may provide insights that aid in the development of improved structural materials for molten salt reactors.

Atomic, electronic, and superconducting properties of Zr[formula omitted]Ir compound

We have investigated the structural, electronic, mechanical, phononic, and superconducting properties of the Zr2Ir compound with a body-centered tetragonal crystal structure using first-principles calculations. Our analysis reveals that the Zr2Ir compound shows mechanical and dynamically stable by using with and without spin–orbit coupling (SOC) effect. After calculating some properties such as elastic constants, Bulk modulus, Young’s modulus, Poisson ratio, Debye temperature, and sound velocity, we found that Zr2Ir is ductile. When the elastic constants C11 and C33 are compared, it is determined that the situation changes in the opposite direction under the effect of SOC, that is, more compressibility along the x-axis turns into the z-axis. Here, the electronic band structure and intensity of the states calculated for the compound show a metallic character. The superconducting critical temperature (Tc) and electron–phonon coupling constant (λ) were found to be 7.50 K and 0.93 without SOC and 7.62 K and 0.96 with SOC, respectively. We determined that although the Zr2Ir compound has a strong electron–phonon coupling regime, the inclusion of SOC slightly reduces its critical temperature and electron–phonon coupling constant.

Pressure-induced Structural Phase Transition and New Superconducting Phase in UTe2

We report on the crystal structure and electronic properties of the heavy fermion superconductor UTe2 at high pressure up to 11 GPa, as investigated by X-ray diffraction and electrical resistivity experiments. The X-ray diffraction measurements under high pressure using a synchrotron light source reveal anisotropic linear compressibility of the unit cell up to 3.5 GPa, while a pressure-induced structural phase transition is observed above PO–T ∼ 3.5–4 GPa at room temperature, where the body-centered orthorhombic crystal structure with the space group Immm changes into a body-centered tetragonal structure with the space group I4/mmm. The molar volume drops abruptly at PO–T, while the distance between the first-nearest neighbor of U atoms, dU–U, increases, implying a switch from the heavy electronic states to the weakly correlated electronic states. Surprisingly, a new superconducting phase at pressures higher than 7 GPa was detected at Tsc > 2 K with a relatively low upper-critical field, Hc2(0). The resistivity above 3.5 GPa, thus, in the high-pressure tetragonal phase, shows a large drop below 230 K, which may also be related to a considerable change from the heavy electronic states to the weakly correlated electronic states.

Investigation of the body-centred tetragonal structure of Fe–Co–V–N Bulk foils using the rolling and ammonia-gas-nitriding method

Improving the properties of permanent magnets is essential for the advancement of electric motors in reducing energy consumption and carbon emissions. This study investigated the effect of V and N addition to FeCo foils on the stability of tetragonally distorted FeCo-based bulk magnets. The incorporation of these two elements stabilised the body-centred tetragonal structure in thin-film and bulk systems. Fe–Co–V ingots were rolled and nitrided by ammonia gas at 650 °C for 5 h. A body-centred tetragonal lattice with an axial ratio of c/a ≈ 1.1 was observed by transmission electron microscopy, and the collected data suggested the induction of a large uniaxial magnetic anisotropy. This study is expected to improve our understanding of rare-earth-free magnets.

Synthesis and Analysis of In2CdO4/Y2SmSbO7 Nanocomposite for the Photocatalytic Degradation of Rhodamine B within Dye Wastewater under Visible Light Irradiation

A new photocatalyst In2CdO4 was prepared by a solid phase sintering synthesis method at high temperature for the first time in this paper. The In2CdO4/Y2SmSbO7 heterojunction (IYH) catalyst was prepared by the solvent thermal method for the first time. The Y2SmSbO7 compound crystallized in the pyrochlore-type architecture and cubelike crystal system, and the space group of Y2SmSbO7 was Fd3m and the crystal cell parameters of Y2SmSbO7 was 9.51349 Å. The band gap width of Y2SmSbO7 was 2.63 eV. In2CdO4 crystallized with a body centered tetragonal lattice structure which was a tetragonal crystal system with a space group of I41/amd. The band gap width of In2CdO4 was 2.70 eV. After 110 minutes of visible light irradiation (VLGI-110min) with IYH as the photocatalyst, the removal rate (RR) of rhodamine B (RhB) concentration was 100% and the total organic carbon (TOC) concentration RR was 99.71%. The power mechanics invariable k toward RhB consistency and visible light irradiation (VLGI) time with IYH as the photocatalyzer reached 0.03073 min−1. The power mechanics invariable k which was involved with TOC reached 0.03621 min−1. After VLGI-110min, the RR of RhB with IYH as the photocatalyzer was 1.094, 1.174 or 1.740 times higher than that with In2CdO4, Y2SmSbO7 or N-doping TiO2 (N-TO) as the photocatalyzer, respectively. The results showed that the photocatalytic activity of IYH was the highest compared with In2CdO4, Y2SmSbO7, or N-TO. With appending a trapping agent, the oxidative capability for degrading RhB, which ranged from strong to weak among three oxidative radical groups, was as follows: hydroxyl radicals &gt; superoxide anion &gt; holes. This work provided a scientific basis for the research which resulted in prosperous development of efficient heterojunction compound catalysts.

Irradiation-induced phases in an Fe ion irradiated CLAM steel

CLAM (HEAT-9) steel samples were subjected to a standard heat treatment involving a normalizing for 0.5 h at 980 °C and a tempering for 1.5 h at 760 °C. The standard heat-treated steel samples were irradiated with 3.5 MeV Fe13+ ions at 400 °C to 0.53 dpa and 0.61 dpa. The precipitate phases of standard heat-treated steel samples and the irradiated steel samples were observed and analyzed using transmission electron microscopies and energy dispersive X-ray spectrometers. Through the analyses of selected-area electron diffraction pattern and energy dispersive X-ray data of thin foil specimens, the effects of irradiation on the main inherent precipitate phases, Cr-rich M23C6 and Ta-rich MX, in standard heat-treated steel were investigated, and three kinds of phases induced by the irradiation were found in the irradiated steel. After irradiation, Cr-rich M23C6 and Ta-rich MX phases were observed and confirmed to be still present in the steel, but the Cr/Fe ratio and W content in the Cr-rich M23C6 precipitates decreased obviously. These three irradiation-induced phases in the irradiated steel were identified as Fe-rich M3C carbide with a simple orthorhombic crystal structure, sigma-FeCr intermetallic compound with a body-centered tetragonal crystal structure, and Fe-Cr binary intermetallic compound with a body-centered cubic crystal structure. The identified Fe-rich M3C/sigma-FeCr/Fe-Cr phases have a metal element composition of 92–98Fe and 2–8Cr/85–95Fe and 5–15Cr/40–90Fe and 10–60Cr (in at.%), and a size range of 80–190/60–190/70–300 nm, respectively. The formation of these three irradiation-induced phases in the steel are also discussed.

Microstructure, precipitation behavior, and properties of quaternary Cu–Be–Co–Ni alloy under electromagnetic levitation

Electromagnetic levitation (EML) can provide a containerless environment and, consequently, large undercooling solidification for various metals. In this study, the microstructures, precipitated phase characteristics, properties, and strengthening mechanisms of Cu–0.2Be–1.6Co–1.6Ni alloy with different undercooling conditions were investigated using the EML method. The achieved undercooling range was 76–315 K. The microstructure of the alloy was mainly composed of dendrites and slender-strip precipitates. Under EML, the length and width of the precipitates decreased by an order of magnitude with increasing undercooling. The precipitates transformed from a α(Co) phase with a face-centered cubic structure to a metastable γ′ phase with a body-centered tetragonal structure. The microhardness increased almost linearly from 120 to 154 HV with enhanced undercooling. The electrical conductivity was higher than that of the master alloy and increased slightly with enhanced undercooling. Quantitative analyses of the strengthening mechanisms revealed the vital roles of solution and precipitation strengthening in the mechanical properties of EML alloys, whereby the former was weakened and the latter was strengthened as undercooling progressed. The simultaneous enhancement of the mechanical and electrical properties of Cu–0.2Be–1.6Co–1.6Ni alloy can be attributed to the increased solute precipitation and refined precipitates due to deep undercooling.

Effect of interlayer temperature and extremely low terminal cooling temperature on the microstructure and wear resistance of Fe-based hardfacing alloy

Hypereutectic high chromium cast iron (HHCCI) coatings were prepared by flux-cored arc welding (FCAW) under 230 °C, 80 °C and 30 °C interlayer temperatures, and an extra liquid nitrogen cooling was used to obtain −125 °C terminal cooling temperature. The microstructure evolution mainly primary carbide (P–C) and matrix, and abrasive wear behavior were evaluated. For natural air cooling, the amount of primary carbide increased, and the size and the mean free path between P–C decreased, with the decrease of the interlayer temperature. Due to the anisotropy in the P–C shape, the volume fraction of P–C, expressed by the area fraction, was significantly affected by the growth orientation. Liquid nitrogen cooling further optimized the morphology of P–C, in terms of the amount, size and distribution. Due to the −125 °C terminal cooling temperature, the martensitic transformation developed in the matrix, showing a body-centered tetragonal structure and exhibiting a Kurjumov-Sachs (K–S) orientation relationship with parent austenite. The linear relationship between wear resistance and P–C was investigated by Pearson's correlation coefficient, and the amount, size and mean free path expressed a strong correlation with wear resistance. Finally, the coating cooled by liquid nitrogen showed the best wear resistance, owing to the excellent morphology of P–C, and the strengthened matrix.

Evolution of austenite lattice parameter during isothermal transformation in a 0.4 C low alloyed steel

The evolution of internal stress during displacive transformation is a topic of continuous debate. Neutron diffraction was used to study the isothermal bainite transformation in a 0.4 C low alloyed steel from 773 to 623 K to provide a clearer basis for discussion regarding the change in the austenite lattice parameter. According to diffraction profile analysis, fresh bainite possesses a body-centered tetragonal structure, and its c/a ratio decreases rapidly over time. The austenite lattice parameter increases or decreases depending on whether the transformation temperature is above or below the nose of the Time-Temperature-Transformation (TTT) curve. This isothermal transformation behavior can be divided into two categories: above and below the nose of TTT curve, which correspond to the upper and lower bainites, respectively. The internal stresses caused by the transformation strains are relaxed by dislocation motion and vacancy formation. The yielded dislocations and vacancies not only affect the broadening of both austenite and bainitic ferrite diffraction peaks but also the lattice parameter. The first-principles calculations demonstrate that the austenite lattice parameter decreases as the vacancy density increases, which may account for the experimental observation in lower bainite.

The Effect of Ni2+ Ions Substitution on Structural, Morphological, and Optical Properties in CoCr2O4 Matrix as Pigments in Ceramic Glazes.

The structural, morphological, and optical properties of Ni2+ ions substitution in CoCr2O4 matrix as ceramic pigments were investigated. The thermal decomposition of the dried gel was performed aiming to understand the mass changes during annealing. The X-ray diffraction (XRD) studies reveal a spinel-type Face-Centered Cubic structure and a secondary Cr2O3 phase when x ≤ 0.75 and a Body-Centered Tetragonal structure when x = 1. Fourier Transform Infrared Spectroscopy (FT-IR) indicated two strong absorption bands corresponding to the metal-oxygen stretching from tetrahedral and octahedral sites, characteristic of spinel structure. Ultraviolet-Visible (UV-Vis) spectra exhibited the electronic transitions of the Cr2+ Cr3+ and Ni2+ ions. From the UV-Vis data, the CIE color coordinates, (x, y) of the pigments were evaluated. The morphology was examined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) showing the agglomeration behavior of the particles. The stability, coloring properties and potential ceramic applications of studied pigments were tested by their incorporation in matte and glossy tile glazes followed by the application of obtained glazes on ceramic tiles. This study highlights the change in pigment color (from turquoise to a yellowish green) with Ni2+ ions substitution in the CoCr2O4 spinel matrix.

Diffusion of hydrogen in the body centered tetragonal hydride phase of the V–H system controlled by multiple substitutional metal elements

The diffusion and site occupation of hydrogen in the monohydride phase (β phase) of the V1−x−yCrxMoy–H (x + y ≤ 0.15) system have been studied by means of proton nuclear magnetic resonance. The β phase has a body centered tetragonal (BCT) structure and hydrogen atoms occupy the octahedral (Oz) sites along the c-axis. Cr has a smaller atomic radius than V but Mo has a larger one, resulting in no obvious change in the unit cell volume of the BCT lattice by substitution of both Cr and Mo for a part of V, although the multiple metal elements of V, Cr, and Mo induce lattice strain and distortion. The temperature dependence of 1H spin-lattice relaxation time has demonstrated that the substitution of both Cr and Mo offsets the change in the activation energy for hydrogen diffusion EH for the Oz sites, while our previous study has indicated that Cr increases EH and Mo decreases that. The diffusion behavior of hydrogen is explained by the dimension of the interstitial sites attributing to the weighted mean atomic radius of the substitutional metal elements, which is independent of their affinities for hydrogen and the lattice strain.