New approaches to preparing powder and ceramics of double perovskite Sr2AlNbO6 (SAN) are presented. In addition to the conventional solid-state method, we employed organic solvents, sol-gel synthesis and liquid precursor plasma spraying (LPPS) to deposit SAN ceramic layers. For these purposes, we used a niobium oxalate complex forming stable solutions or gels in DMF with Sr2+ and Al3+ nitrates. We investigated the composition and thermal behavior of solutions, gels and prepared SAN samples and found that DMSO containing Nb precursor yields a stable impurity phase Sr4Al6O12(SO4) inside the final SAN powder. The measured linear thermal expansion coefficient (TEC) of sintered SAN is 12.4 & times; 10-6 K-1 at 1000 degrees C, which exceeds that for yttriastabilized zirconia, YSZ (11 & times; 10-6 K-1). The LPPS SAN coating contains two phases, identified as SAN and an amorphous oxide. The Young's modulus and Vickers nanohardness of SAN in LPPS-coating are also better than those of YSZ coating deposited with conventional atmospheric plasma spraying (APS).

The T-x phase diagram of the Na2MoO4-Li2MoO4 system was revised and two compounds, Na7Li(M & ocy;O4)4 (exists above 435 degrees C) and Na3-xLi1+x(MoO4)2 (0 <= x <= 0.2) were found, which melt incongruently at 544 and 515 degrees C, respectively. Orthorhombic Na7Li(M & ocy;O4)4 of a new structure type contains the [Li(MoO4)4]7- clusters of the central LiO4 tetrahedron sharing vertices with four MoO4 tetrahedra; the clusters are connected through NaO6 and NaO5 polyhedra in two types of layers, which alternate along the c axis. In monoclinic Na2.82Li1.18(MoO4)2, isostructural with Na3Li(MoO4)2, the trigonal bipyramids of NaO5 and (Na, Li)O5 share edges to form six- membered ribbons arranged along (101) in parquet-like layers resembling cuspidine-like layers with four- membered ribbons in Na7Li(M & ocy;O4)4. The layers in Na 2.82 Li 1.18 (MoO 4 ) 2 are connected by the MoO4 and LiO4 tetrahedra into a 3D framework. Under metastable crystallization conditions, the spinel-type Li2MoO4(sp) crystals were also obtained and structurally studied. Calculations of bond-valence-based energy barriers for potential diffusion of the lithium and sodium ions show probable 1D sodium-ion conductivity for Na7Li(M & ocy;O4)4. Possible 3D lithium-ion transport pathway in Li2MoO4(sp) passes through common triangular faces surrounding Li in octahedral 16d position and empty tetrahedral 8b site.

Thermal barrier coatings are crucial for industries like aerospace and energy that rely on high temperatures, shielding metal, ceramic, or composite components from heat damage. Yttria-stabilized zirconia is one of the best thermal barrier coating (TBC) material due to its high-temperature stability and oxidation resistance, but it has drawbacks such as thermal phase transition at 1150-1200°C and high oxygen conductivity limit the number of thermal cycles and operating temperature at 1200°C. Thus, it is essential to find new TBC materials with low thermal conductivity, high thermal expansion coefficient, high phase, and thermal, mechanical, and chemical stability under oxidizing conditions to enhance performance and efficiency. In this study, using advanced computational methods, including AI and molecular dynamics simulations, we proposed several promising complex oxides with suitable structures, thermal and mechanical properties that could be further studied experimentally as TBC materials. Having calculated thermophysical properties of complex oxides with structures of perovskite, pyrochlore, garnet, and their derivatives. Using rigorous criteria, we have identified 14 new compounds with potential TBC applications. Overall, this research highlights the importance of computational techniques in material discovery for TBC applications.

Low thermal conductivity is important for thermal barrier coatings, thermoelectrics, and other applications in industry and materials science. Accurate calculation of their thermal conductivity kappa at high temperatures remains challenging: methods such as the Boltzmann transport equation (BTE) usually underestimate the actual value. Here we used the effective harmonic method and homogeneous nonequilibrium molecular dynamics simulations with machine-learning potentials to calculate the thermal conductivity of candidate materials at temperatures up to 1500 K. The results obtained for La2Zr2O7, ZrSiO4, and BaZrO3 are in perfect agreement with the experiment at all temperatures. We used renormalized second- and third-order interatomic force constants and phonons at high temperatures to calculate the thermal conductivity using the BTE and confirmed these results with molecular dynamics simulations. Investigating the relationship of thermal conductivity with the elastic properties, Debye temperature, and the speed of sound, we proposed threshold values for future high-throughput screening for low kappa materials. Using the molecular dynamics method at high temperatures, we calculated the volumetric thermal expansion coefficient and selected ten candidate materials for thermal barrier coatings at high temperatures. Besides thermal barrier coating materials, this approach can be applied to multiple classes of materials where thermal conductivity is important.

Widespread commercialization of sodium-ion batteries (SIB) is limited by the shortcomings of existing electrode materials, so the search and testing of various sodium compounds suitable for SIB are relevant. This paper presents the results of a study of the sodium diffusion mechanisms in quasi-layered oxides Na1-xV1-xMo1+xO6, which are potentially promising for applications for SIB. A simple synthesis procedure has been developed, which makes it possible to obtain compounds in a wide range of compositions up to x = 0.2. To elucidate the mechanisms of sodium diffusion, we applied a comprehensive approach that combines material characterization at the “macro” (XRD, impedance spectroscopy) and “atomic-scale” levels (NMR, ab-initio calculations). Our results reveal rather fast sodium dynamics: Ionic conductivity reaches the values of 10–3 S/cm at T > 730 K. It has been found moreover that the diffusion mechanism changes with increasing temperature. At T < 625 K, sodium motion occurs mainly along the crystallographic b axis due to atomic jumps with the shortest jump length ≈ 3.6 Å and activation energy Ea 1 eV. With increasing temperature, another type of jumps along a axis (in the ab plane) with a jump length of ≈ 5 Å and a barrier value of 2 eV is also activated.

The milestones of the development of X-ray diffraction and crystal chemical studies in the Laboratory of Crystal Chemistry of the Nikolaev Institute of Inorganic Chemistry SB RAS for 1958-2024 are highlighted.

In this study we present the results of our density functional theory calculations within the quasi-harmonic approximation, which predict formation and properties of a new compound of the garnet family, La 3 Sc 2 Al 3 O 12 (LSAG). LSAG was shown to be formed from 3LaAlO 3 + Sc 2 O 3 at ambient pressure and room temperature. The thermodynamic stability region of LSAG is limited by a temperature of 685 K, above which its decomposition into LaAlO 3 (LAP) and Sc 2 O 3 occurs. With increasing pressure, LSAG retains its stability up to 0.23 GPa, where the decomposition reaction LSAG <-> 3LAP + Sc 2 O 3 becomes thermodynamically favorable. In this work, not only the thermodynamic stability of LSAG was assessed, but also its thermal conductivity, elastic constants and band gap were calculated. At 300 K the thermal conductivity of LSAG is 13.204 Wm -1 K -1 . LSAG has the smallest elastic constants compared with YSAG and YAG, which indicates weaker atomic bonding in LSAG than in YSAG and YAG. The width of band gap of LSAG calculated using an hybrid functional is equal to 5.24 eV. In addition, the P-T phase diagram of the known Y 3 Sc 2 Al 3 O 12 (YSAG) was calculated for the first time. Unlike LSAG, YSAG is stable at fairly high temperatures, reaching values of at least 1500 K. With increasing temperature to 1500 K, the pressure of the phase transition increases slightly to 3.55 GPa, and the monovariant curve of the reaction YSAG <-> 3YAP+Sc 2 O 3 is represented by an almost straight line.

In this study we present the results of our density functional theory calculations within the quasi-harmonic approximation, which predict formation and properties of a new compound of the garnet family, La3Sc2Al3O12 (LSAG). LSAG was shown to be formed from 3LaAlO3 + Sc2O3 at ambient pressure and room temperature. The thermodynamic stability region of LSAG is limited by a temperature of 685 K, above which its decomposition into LaAlO3 (LAP) and Sc2O3 occurs. With increasing pressure, LSAG retains its stability up to 0.23 GPa, where the decomposition reaction LSAG↔3LAP+ Sc2O3 becomes thermodynamically favorable. In this work, not only the thermodynamic stability of LSAG was assessed, but also its thermal conductivity, elastic constants and band gap were calculated. At 300 K the thermal conductivity of LSAG is 13.204 Wm−1K−1. LSAG has the smallest elastic constants compared with YSAG and YAG, which indicates weaker atomic bonding in LSAG than in YSAG and YAG. The width of band gap of LSAG calculated using an hybrid functional is equal to 5.24 eV. In addition, the P–T phase diagram of the known Y3Sc2Al3O12 (YSAG) was calculated for the first time. Unlike LSAG, YSAG is stable at fairly high temperatures, reaching values of at least 1500 K. With increasing temperature to 1500 K, the pressure of the phase transition increases slightly to 3.55 GPa, and the monovariant curve of the reaction YSAG↔3YAP+Sc2O3 is represented by an almost straight line.

A 60-year-old problem with the atomic arrangements and exact compositions of alkali polytungstates related to hexagonal tungsten bronze (HTB) was solved. The systems A2WO4-WO3 (A = K, Rb) were restudied and the average monoclinic layered structures of stoichiometric polytungstates A4W11O35 (A = K, Rb, Cs, Tl) and A2W7O22 (A = K, Rb, Cs) were first successfully determined. The structures resemble those of "MoW11O36" and "MoW14O45" (J. Graham and A. D. Wadsley, Acta Crystallogr., 1961, 14, 379-383) and are derived from HTB by breaking into slabs parallel to (100) due to the ordered omission of some [WO]∞ chains along the hexagonal tunnels. The slabs in A4W11O35 (A = Cs, Tl) and A2W7O22 (A = Rb, Cs) are mutually shifted by the a/2 HTB unit cell axis. These data mainly confirmed our preliminary structural models of HTB-like alkali polytungstates (S. F. Solodovnikov, N. V. Ivannikova, Z. A. Solodovnikova and E. S. Zolotova, Inorg. Mater., 1998, 34, 845-853) and revealed a new similar thallium polytungstate. The structures of the HTB-like polytungstates and related compounds form a homologous series of layered complex oxides or fluorides An+2-xM3n+2X9n+8 where n = 2, 3 and 4 are equal to the numbers of HTB hexagonal tunnels across the polytungstate slab width for Tl2W4O13, A4W11O35 and A2W7O22 (A = K, Rb, Cs or Tl), respectively. The structures of the HTB-like polytungstates seem to intergrow with HTB-type AxWO3 to form, in particular, higher homologues of the series. Our group-supergroup analysis, measurements of nonlinear optical activity and electrical conductivity, and calculations of the bond-valence site energy barriers indicate possible ferroelectric/ferroelastic properties and moderate 2D oxide-ion mobility within the HTB-type slabs of the studied polytungstates.

The phase formation in the Na 2 MoO 4 -Cs 2 MoO 4 -NiMoO 4 system is studied using the solid-state synthesis and flux crystallization. The formation of a cesium-containing solid solution based on double molybdate Na 4-2 x Ni 1+ x (MoO 4 ) 3 of the alluaudite type and new triple molybdate of a related structure is established. Their structures contain layers of МоО 4 tetrahedra and coupled (Ni, Na)O 6 octahedra bridged by МоО 4 tetrahedra into three-dimensional open frameworks with tunnels along the c axis filled by sodium cations. By the example of isostructural Na 3.39 Ni 1.31 (MoO 4 ) 3 (I) and Na 3.18 Cs 0.29 Ni 1.26 (MoO 4 ) 3 (II), it is shown that in the alluaudite-type solid solution, cesium ions partially replace sodium cations in the framework tunnels, which provides the sodium ion conductivity. The structure of triple molybdate Na 2.64 Cs 0.64 Ni 1.36 (MoO 4 ) 3 (III) is a new type of the alluaudite superstructure deformed and tripled in volume. Its formation is caused by a significant differentiation of cations at (Ni, Na) and (Na, Cs) positions. In terms of the degree of deformation, this structure is intermediate between alluaudite and (pseudo)orthorhombic Na 10 Cs 4 M 5 (MoO 4 ) 12 ( M = Mn, Co) and Na 25 Cs 8 R 5 (MoO 4 ) 24 ( R = Fe, Sc, In). Among the crystallization products in the Na 2 MoO 4 -Cs 2 MoO 4 -NiMoO 4 system, crystals with a similar incommensurate modulation of the alluaudite structure along the c axis are found. Calculations of bond valence sum maps for sodium ions in the structures of I–III confirm the possibility of the one-dimensional sodium-ion conductivity for them at its lowest threshold for double molybdate for which the two-dimensional transport is also probable at elevated temperatures.

С помощью твердофазного синтеза и раствор-расплавной кристаллизации изучено фазообразование в системе Na2MoO4-Cs2MoO4-NiMoO4, установлено образование цезийсодержащего твердого раствора на основе двойного молибдата Na4-2xNi1+x(MoO4)3 типа аллюодита и нового тройного молибдата родственного строения. Их структуры содержат слои МоО4-тетраэдров и спаренных октаэдров (Ni, Na)O6, которые связаны мостиковыми МоО4-тетраэдрами в трехмерные ажурные каркасы с туннелями вдоль оси c, заполненными катионами натрия. На примере изоструктурных Na3.39Ni1.31(MoO4)3 (I) и Na3.18Cs0.29Ni1.26(MoO4)3 (II) показано, что ионы цезия в твердом растворе типа аллюодита частично замещают катионы натрия в туннелях каркаса, которые обеспечивают натрий-ионную проводимость. Структура тройного молибдата Na2.64Cs0.64Ni1.36(MoO4)3 (III) является новым типом деформированной и утроенной по объему сверхструктуры аллюодита, образование которой вызвано значительной дифференциацией катионов в позициях (Ni, Na) и (Na, Cs). Эта структура по степени деформации занимает промежуточное положение между аллюодитом и (псевдо)ромбическими Na10Cs4M5(MoO4)12 (M = Mn, Co) и Na25Cs8R5(MoO4)24 (R = Fe, Sc, In). Среди продуктов кристаллизации в системе Na2MoO4-Cs2MoO4-NiMoO4 найдены кристаллы с аналогичной несоразмерной модуляцией структуры аллюодита вдоль оси c. Расчеты карт сумм валентных усилий для ионов натрия в структурах I–III подтвердили для них возможность одномерной натрий-ионной проводимости при наиболее низком ее пороге у двойного молибдата, для которого при повышенных температурах вероятен и двухмерный транспорт.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Development of the technologies for energy storage and conversion requires a search for compounds with high diffusion of alkali and alkaline-earth ions. Here, we present the results of comprehensive studies, including synthesis, powder X-ray diffraction, experiments on impedance and Na-23 NMR spectroscopy, as well as ab initio calculations, which were carried out to explore the sodium diffusion in scheelite-like Na5M(MoO4)(4) with M = Y, La, Bi, and in related solid solutions Na5-xM1-xZrx(MoO4)(4) (0.05 <= x <= 0.1), which were synthesized for the first time. Our investigations reveal that the Na-ion mobility increases in the sequence Y -> La -> Bi and with growing x. For Na4.9Bi0.9Zr0.1(MoO4)(4) the highest ion conductivity was found: similar to 10(-4) S/cm at T = 450 degrees C, which is comparable to that of the NASICON-type molybdates. From the temperature variations of the Na-23 NMR spectra and DFT calculations, the mechanism of sodium-ion diffusion was established at the atomic-scale level.

In the present study, P-T phase diagrams of ZrO2 and HfO2 for a wide pressure range of 0-150 GPa at 0-2500 K were calculated for the first time using density functional theory with the method of lattice dynamics within the quasi-harmonic approximation. We calculated P-T conditions for a full sequence of high-pressure transformations, P21/c → Pbca → Pnma → P6̄2m, for both compounds. At low temperatures, these transformations for ZrO2 are obtained at 7.6 GPa (P21/c → Pbca), 13.4 GPa (Pbca → Pnma), and 143 GPa (Pnma → P6̄2m), while for HfO2 similar polymorphic transitions are obtained at 9 GPa (P21/c → Pbca), 16 GPa (Pbca → Pnma), and 126 GPa (Pnma → P6̄2m), correspondingly. At high temperatures, for both ZrO2 and HfO2 the P21/c and Pbca structures transform into the P42/nmc modification. In addition, the thermal conductivity and elastic properties of the ZrO2 and HfO2 polymorphs were calculated and compared with the available experimental and theoretical data.

New key data were obtained to solve old problems with the compositions and structures of the polytungstates related to the hexagonal tungsten bronze (HTB). The systems A2WO4-WO3 (A = K, Rb) were restudied and formation of K2W2O7, A2W3O10, K2W4O13, A4W11O35, and A2W7O22 was confirmed. The average monoclinic layered structures of A4W11O35 (A = K, Rb, Cs, Tl) and A2W7O22 (A = K, Rb, Cs) resembling those of “MoW11O36” and “MoW14O45” (Graham & Wadsley, 1961) were first solved. The structures are derived from the HTB by breaking into slabs parallel to (100) due to ordered omission of some [WO]µ chains along to hexagonal tunnels. The slabs in A4W11O35 (A = Cs, Tl) and A2W7O22 (A = Rb, Cs) are mutually shifted by the a/2 HTB unit cell axis. These data mainly confirmed our preliminary structure models of the HTB-like alkali polytungstates and revealed a new similar thallium polytungstate. The structures of the HTB-like polytungstates and related compounds forms the homologous series of layered complex oxides or fluorides An+2-xM3n+2X9n+8 where n = 2, 3 and 4 are equal to the numbers of the HTB hexagonal tunnels across the polytungstate slab width for Tl2W4O13, A4W11O35 and A2W7O22 (A = K, Rb, Cs or Tl), respectively. The structures of the HTB-like polytungstates seem to be able intergrowing with the HTB-type AxWO3 to form, in particular, higher homologues of the series. Our group-supergroup analysis, measurements of nonlinear optical activity, electrical conductivity and calculations of the bond-valence site energy barriers indicate possible ferroelectric/ferroelastic properties and moderate oxide-ion mobility within the HTB-type slabs of the studied polytungstates.

The subsolidus phase equilibria in the system Ag2MoO4-Rb2MoO4-Sc-2(MoO4)(3) were studied and two new triple molybdates, Rb9Ag3Sc2(MoO4)(9) and Rb7Ag5Sc2(MoO4)(9), were found. The structures of Rb7Ag5Sc2(MoO4)(9) and isostructural Rb7Ag5Sc2(WO4)(9) of the Cs7Na5Yb2(MoO4)(9) type (the space group 32) were determined. The found composition of the triple tungstate crystal, Rb7Ag4.61Sc2.13(WO4)(9), indicates a non-stoichiometric compound formula, Rb7Ag5-3xSc2+x(WO4)(9). Both structures have one incompletely occupied Ag site, and structure Rb7Ag4.61Sc2.13(WO4)(9) also contains two positions with mixed Ag and Sc. Both compounds contain 'lanterns' [M-2(XO4)(9)] (M = (Sc, Ag), Sc; X = Mo, W), which are strengthened by three AgO2 dumbbells to give isolated building blocks [Ag3M2(XO4)(9)] forming two-story hexagonal layers resembling the structure of glaserite K3Na(SO4)(2). Similar layers of [Ag3Sc2(WO4)(9)](9-) building blocks were also found by us in the structure of Rb9-xAg3+xSc2(WO4)(9), which is close to that of Rb9Ag3Sc2(MoO4)(9). Similar layers of the [M-2(TO4)(9)] units were also observed in Cs7Na5Yb2(MoO4)(9) and Na13Sr2Ta2(PO4)(9). The title compounds belong to the series of rhombohedral triple molybdates and tungstates with a approximate to 9-10 angstrom and large c-periods (more than 20 angstrom), which have layered or open 3D framework structures. Like many compounds of this series, Rb7Ag5Sc2(XO4)(9) (. = W, Mo) at elevated temperatures have significant ionic conductivity reaching values 6.1.10(-3) S cm(-1) at 703 K (X = Mo) and 1.4.10(-3) S cm(-1) at 733 K (X = W) with E-a = 0.7 eV and 0.6 eV, respectively.

The work reviews the structure, non-stoichiometry, and ionic mobility of molybdates, tungstates, and other compounds crystallizing in the structure type of alluaudite (Na, Ca)(Fe, Mn, Mg)3(PO4)3 with the general Moore′s crystal chemical formula X(2)X(1)M(1)M(2)2(TO4)3, where X are large cations Na+, Ca2+, K+, Pb2+, etc., with the coordination number 8; M are octahedral cations, T = P, As, V, S, Mo, W. Using this formula and the corresponding site occupancies, possible limits of double molybdate and tungstate compositions of the alluaudite family are determined. Various types of distortions (superstructures) of alluaudite are considered; several groups of phases with different symmetries, numbers of anions in the unit cell, and vector relations with the unit cell of the original alluaudite structure are distinguished. It is shown that chains of partially defective positions X(2) and X(1) aligned along axis c play a key role in the transport of sodium cations in the alluaudite type phases. Phosphates and sulfates with alluaudite structure exhibit mainly 1D transport of sodium ions; however, calculations of the bond-valence sum maps, NMR data, and ab initio calculations show that 2D transport in the (100) plane is possible in complex molybdates and tungstates due to the transport of Na+ ions between X(2)–X(2) and X(1)–X(1) channels through the bridging site M(1). It is shown that the family of alluaudite-related (pseudo)orthorhombic triple molybdates Na10Cs4M5(MoO4)12 (M = Mn, Co) and Na25Cs8R5(MoO4)24 (R = Fe, Sc, In) also exhibits 2D diffusion of sodium ions via successive zigzag ion hoppings and that 3D transport may appear at elevated temperatures.

Рассмотрены особенности строения, нестехиометрия и ионная подвижность молибдатов, вольфраматов и других соединений, кристаллизующихся в структурном типе аллюодита (Na, Ca)(Fe, Mn, Mg)3(PO4)3 с общей кристаллохимической формулой по П. Муру X(2)X(1)M(1)M(2)2(TO4)3, где X — крупные катионы Na+, Ca2+, K+, Pb2+ и др. с КЧ = 8; M — октаэдрические катионы, T = P, As, V, S, Mo, W. На основе этой формулы и заселенностей соответствующих позиций выведены возможные пределы составов двойных молибдатов и вольфраматов типа аллюодита. Рассмотрены виды искажения (сверхструктуры) аллюодита, выделено несколько групп фаз, различающихся симметрией, числом анионов в ячейке и векторной связью с ячейкой исходной структуры аллюодита. Показано, что ключевую роль в переносе катионов натрия в фазах типа аллюодита играют цепочки частично дефектных позиций X(2) и X(1), идущие вдоль оси c. Для фосфатов и сульфатов со структурой аллюодита характерен преимущественно одномерный транспорт ионов натрия, однако, согласно данным расчетов карт сумм валентных усилий, ЯМР спектроскопии и ab initio расчетов, в сложных молибдатах и вольфраматах есть возможность двухмерной проводимости в плоскости (100) за счет перетока ионов Na+ между каналами X(2)—X(2) и X(1)—X(1) через мостиковую позицию M(1). Показано, что в семействе родственных аллюодиту (псевдо)ромбических тройных молибдатов Na10Cs4M5(MoO4)12 (M = Mn, Co) и Na25Cs8R5(MoO4)24 (R = Fe, Sc, In) также возможна двухмерная диффузия ионов натрия через последовательные зигзагообразные ионные перескоки с вероятной реализацией трехмерного транспорта при повышенных температурах.

Alluaudite-type compounds are currently considered as a promising class of materials for sodium-ion batteries, and understanding of the diffusion processes in them is very important. Using the Na-23 MAS NMR and ab initio calculations, we established the mechanism of sodium diffusion in Na4-2xM1-x(MoO4)(3) (M = Mg, Zn, Cd) depending on the type of M-element and x. A comparison of the results obtained for various alluaudite-type compounds shows the crucial effect of the M-cation on the Na-ion dynamics in this class of materials. Higher concentration and charge of M-element increase the concentration of vacancies in the Na-sublattice and enhance the sodium mobility. Moreover, the Na dynamics increases with the M-ion size. The occupancy of the M site and the type of T atom in the TO4 group also determine the mechanism of sodium diffusion in alluaudites, whether it is one-dimensional or two-dimensional. These findings may help a deeper understanding of sodium diffusion processes in alluaudite-type compounds and their development as materials for sodium-ion batteries.