Uncovering cation disorder in ternary Zn1+xGe1−x(N1−xOx)2 and its effect on the optoelectronic properties

Ternary nitride materials, such as ZnGeN2, have been considered as hopeful optoelectronic materials with an emphasis on sustainability. Their nature as ternary materials has been ground to speculation of cation order/disorder as a mechanism to tune their bandgap. We herein studied the model system Zn1+xGe1−x(N1−xOx)2 including oxygen – which is often a contaminant in nitride materials – using a combination of X-ray and neutron diffraction combined with elemental analyses to provide direct experimental evidence for the existence of cation swapping in this class of materials. In addition, we combine our results with UV-VIS spectroscopy to highlight the influence of disorder on the optical bandgap

Effects of Cr Doping and Water Content on the Crystal Structure Transitions of Ba₂In₂O₅

Temperature-dependent crystal structure alterations in the brownmillerite-type material Ba₂In₂O₅ play a fundamental role in its applications: (i) photocatalytic CO₂ conversion; (ii) oxygen transport membranes; and (iii) proton conduction. This is connected to a reversible uptake of up an equimolar amount of water. In this study, in situ X-ray and neutron diffraction were combined with Raman spectroscopy and solid-state nuclear magnetic resonance experiments to unravel the effects of Cr doping and water content on the crystal structure transitions of Ba₂In₂O₅(H₂O)x over a wide temperature range (10 K ≤ T ≤ 1573 K, x < 1). A mixture of isolated and correlated protons was identified, leading to a highly dynamic situation for the protons. Hence, localisation of the protons by diffraction techniques was not possible. Cr doping led to an overall higher degree of disorder and stabilisation of the tetragonal polymorph, even at 10 K. In contrast, a further disordering at high temperatures, leading to a cubic polymorph, was found at 1123 K. Cr doping in Ba₂In₂O₅ resulted in severe structural changes and provides a powerful way to adjust its physical properties to the respective application

Chemically Controllable Magnetic Transition Temperature and Magneto-Elastic Coupling in MnZnSb Compounds

International audienceMagneto-caloric materials offer the possibility to design environmentally friendlier thermal management devices compared to the widely used gas-based systems. The challenges to develop this solid-state based technology lie in the difficulty of finding materials presenting a large magneto-caloric effect over a broad temperature span together with suitable secondary appli-cation parameters such as low heat capacity and high thermal conductivity. A series of compounds derived from the PbFCl structure is investigated using a combination of computational and experimental methods focusing on the change of cell volume in magnetic and non-magnetic ground states. Scaling analysis of the magnetic properties determines that they are second order phase transition ferromagnets and that the magnetic entropy change is driven by the coupling of magneto-elastic strain in the square-net through the magnetic transition determined from neutron and synchrotron X-ray diffraction. The primary and secondary application related properties are measured experimentally, and the c/a parameter is identified as an accurate proxy to control the magnetic transition. Chemical substitution on the square-net affords tuning of the Curie temperature over a broad temperature span between 252 and 322 K. A predictive machine learning model for the c/aparameter is developed to guide future exploratory synthesis

Research data supporting "Crystal structure and specific heat of calcium lanthanide oxyborates Ca4LnO(BO3)3"

Research data supporting the publication "Crystal structure and specific heat of calcium lanthanide oxyborates Ca4LnO(BO3)3". This project also formed part of Nicola Kelly's PhD research (2018-2022). Data collected includes powder X-ray diffraction (PXRD), powder neutron diffraction (PND), and heat capacity. Please see the file directory.txt for further details on the files.Beamtime awarded by the ILL, Grenobl

Crystal structure and specific heat of calcium lanthanide oxyborates Ca4LnO(BO3)3

Calcium lanthanide oxyborates Ca4LnO(BO3)3 are of interest for their optical and electromechanical properties. Their crystal structure has been well characterised using powder and single-crystal X-ray diffraction but there remains some disagreement regarding cation ordering in these compounds. In this study, combined X-ray and neutron powder diffraction was employed to study the cation distribution and obtain accurate boron and oxygen atomic coordinates for six Ca4LnO(BO3)3 compounds (Ln = Pr, Nd, Tb, Ho, Er, Yb) at room temperature and one (Ln = Tb) at 50 K and 1.5 K. All compounds adopt the previously reported monoclinic structure with space group . The Ln3+ ions are disordered over two of the three metal sites, with the extent of disorder increasing across the lanthanide series with decreasing ionic radius. Low-temperature neutron data for Ca4TbO(BO3)3 showed a decrease in paramagnetic scattering on cooling but no obvious magnetic Bragg or diffuse scattering at the lowest temperature of 1.5 K. We report specific heat data at cryogenic temperatures for eight Ca4LnO(BO3)3 compounds and relate the magnetic properties of these compounds to their structural behaviour.Institut Laue-Langevin (ILL) EP/R513180/1, EP/M000524/1, EP/T028580/

Виявлення фізико-хімічних особливостей вуглецевотремічного відновлення окалини вольфрамових швидкоріжучих сталей

We determined that scale of the high-speed steel R18 is composed of the phases of Fe3O4, Fe2O3, FeO, with the presence of alloying elements as the replacement atoms. The microstructure is disordered and non-uniform. In the examined area, in addition to Fe, we revealed the presence of, % by weight: W – 16.34, Cr – 2.68, V – 1.82, and others. The content of O was 15.32 %. It was established that the reduction of scale at 1,523 K proceeds with the formation of α-Fe and carbides Fe3W3C, (Fe, Cr)7C3, W2C, V2C, Fe3C, Fe2C. Manifestation of carbides of alloying elements decreased with an increase in the degree of reduction. The microstructure of reduction products is heterogeneous, containing particles with a different content of alloying elements and has a spongy structure. The conditions are provided for the absence of phases subject to sublimation. We conducted experimental-industrial tests of using the metallized scale while smelting high-speed steel with a degree of disposal of alloying elements at the level of 92‒94 %. Improvement of environmental safety was implemented by the replacement of reduction melting with the newest methods of powder metallurgy employing the solid-phase reduction.Определены физико-химические превращения при углеродотермическом восстановлении техногенных оксидных отходов производства быстрорежущей стали Р18. Обнаружено протекание химических реакций восстановления и карбидообразования при участии железа и легирующих элементов. Отсутствие фаз склонных к сублимации, повышенная восстановительная способность, губчатая микроструктура обеспечивают относительно высокую степень извлечения тугоплавких элементов при использовании полученного материала в качестве легирующей добавкиВизначено фізико-хімічні перетворення при вуглецевотермічному відновленні техногенних оксидних відходів виробництва швидкоріжучої сталі Р18. Виявлено протікання хімічних реакцій відновлення та карбідоутворення за участю заліза та легуючих елементів. Відсутність фаз схильних до сублімації, підвищена відновна здатність, губчаста мікроструктура забезпечують відносно високий ступінь вилучення тугоплавких елементів при використанні отриманного матеріалу як легуючої добавк

Self-assembled dynamic perovskite composite cathodes for intermediate temperature solid oxide fuel cells

Electrode materials for intermediate temperature (500 – 700 °C) solid oxide fuel cells require electrical and mechanical stability to maintain performance during the cell lifetime. This has proven difficult to achieve for many candidate cathode materials and their derivatives with good transport and electrocatalytic properties because of reactivity towards cell components, and the fuels and oxidants. Here we present Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0.3125O3-δ (BSCFW), a self-assembled composite prepared through simple solid state synthesis, consisting of B-site cation ordered double perovskite and disordered single perovskite oxide phases. These phases interact by dynamic compositional change at the operating temperature, promoting both chemical stability through the increased amount of W in the catalytically active single perovskite provided from the W-reservoir double perovskite, and microstructural stability through reduced sintering of the supported catalytically active phase. This interactive catalyst-support system enabled stable high electrochemical activity through the synergic integration of the distinct properties of the two phases

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo4Se8

[Image: see text] In the lacunar spinels, with the formula AB(4)X(8), transition-metal ions form tightly bound B(4) clusters resulting in exotic physical properties such as the stabilization of Néel-type skyrmion lattices, which hold great promise for energy-efficient switching devices. These properties are governed by the symmetry of these compounds with distortion of the parent noncentrosymmetric F4̅3m space group to the polar R3m, with recent observation of a coexisting Imm2 low-temperature phase. In this study, through powder neutron diffraction, we further confirm that a metastable Imm2 coexists with the R3m phase in GaMo(4)Se(8) and we present its structure. By applying the mode crystallography approach to the distortions together with anisotropic microstrain broadening analysis, we postulate that the formation origin of the minority Imm2 phase stems from the high compressive stress observed in the R3m phase. Bond valence sum analysis also suggests a change in electronic configuration in the transition to Imm2 which could have implications on the electrical properties of the compound. We further establish the nature of the magnetic phase transition using critical exponent analysis obtained from single-crystal magnetization measurements which shows a mixture of tricritical mean-field and 3D Heisenberg behavior [β = 0.22(4), γ = 1.19(1), and δ = 6.42(1)]. Magnetoentropic mapping performed on a single crystal reveals the signature of a positive entropy region near the magnetic phase transition which corresponds to the skyrmion phase field observed in a polycrystalline sample

Виявлення фізико-хімічних особливостей вуглецевотремічного відновлення окалини вольфрамових швидкоріжучих сталей

We determined that scale of the high-speed steel R18 is composed of the phases of Fe3O4, Fe2O3, FeO, with the presence of alloying elements as the replacement atoms. The microstructure is disordered and non-uniform. In the examined area, in addition to Fe, we revealed the presence of, % by weight: W – 16.34, Cr – 2.68, V – 1.82, and others. The content of O was 15.32 %. It was established that the reduction of scale at 1,523 K proceeds with the formation of α-Fe and carbides Fe3W3C, (Fe, Cr)7C3, W2C, V2C, Fe3C, Fe2C. Manifestation of carbides of alloying elements decreased with an increase in the degree of reduction. The microstructure of reduction products is heterogeneous, containing particles with a different content of alloying elements and has a spongy structure. The conditions are provided for the absence of phases subject to sublimation. We conducted experimental-industrial tests of using the metallized scale while smelting high-speed steel with a degree of disposal of alloying elements at the level of 92‒94 %. Improvement of environmental safety was implemented by the replacement of reduction melting with the newest methods of powder metallurgy employing the solid-phase reduction.Определены физико-химические превращения при углеродотермическом восстановлении техногенных оксидных отходов производства быстрорежущей стали Р18. Обнаружено протекание химических реакций восстановления и карбидообразования при участии железа и легирующих элементов. Отсутствие фаз склонных к сублимации, повышенная восстановительная способность, губчатая микроструктура обеспечивают относительно высокую степень извлечения тугоплавких элементов при использовании полученного материала в качестве легирующей добавкиВизначено фізико-хімічні перетворення при вуглецевотермічному відновленні техногенних оксидних відходів виробництва швидкоріжучої сталі Р18. Виявлено протікання хімічних реакцій відновлення та карбідоутворення за участю заліза та легуючих елементів. Відсутність фаз схильних до сублімації, підвищена відновна здатність, губчаста мікроструктура забезпечують відносно високий ступінь вилучення тугоплавких елементів при використанні отриманного матеріалу як легуючої добавк

Proton Conduction and Long-Range Ferrimagnetic Ordering in Two Isostructural Copper(II) Mesoxalate Metal–Organic Frameworks

Two compounds of formula {(H₃O)­[Cu₇(Hmesox)₅(H₂O)₇]·9H₂O}_<i>n</i> (<b>1a</b>) and {(NH₄)_0.6(H₃O)_0.4[Cu₇(Hmesox)₅(H₂O)₇]·11H₂O}_<i>n</i> (<b>1b</b>) were prepared and structurally characterized by single-crystal X-ray diffraction (H₄mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal–organic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper­(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a <i>T</i>_c of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 × 10^–5 S cm^–1 and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper­(II) mesoxalate anionic network