The effect of unstabilized zirconium dioxide on the processes of formation of composite ceramics from industrial corundum powders heat-treated at temperatures of 1430 and 1580?C, changes in its microstructure and physical and mechanical properties have been investigated. It was shown that due to the rigid corundum matrix, unstabilized ZrO2 is preserved mainly in the tetragonal phase. When ceramics are sintered during heat and self-diffusion, zirconium particles are located along the grain boundary of the corundum matrix and fill the pore space. The sintering effect of amorphous SiO2 also contributes to the increased density of ceramics. A two-stage sintering mode provides a finer-grained microstructure of ceramics. It was shown that due to the presence of a larger number of ZrO2 grains capable of t-m-transformation at the Al2O3 boundaries, the resistance of composite ceramics to mechanical and thermal loads increases. Ceramics obtained at 1580?C and containing 6.0 wt. % t-ZrO2 possesses the maximum hardness of 17 GPa. Dilatometric characteristics and the values of the relative shrinkage of composite samples are given.

The high-entropy oxide (HEO) Sr(Ce0.05Sn0.08Zr0.2Ti0.16Y0.3Nb0.11Al0.1)O-2.9 with a significant B-sublattice cation size deviation, was predicted by thermodynamic approach and synthesized via a conventional solid-state route at 1500-1600 degrees C. The thermodynamic findings revealed an energy minimum at 623 degrees C, influencing the stability of the HEO. These insights highlight the temperature limitations for synthesis (<1623 degrees C) and underscore the impact of the composition on overall stability. Microstructure analysis demonstrates reactive sintering, resulting in a dense (90-93 %) low-porosity sample. EDS and mapping reveal uniform dispersion cations with minimal Ce0.86Y0.14O1.93 impurity grain formation. The stability of the perovskite-like structure was assessed based on factors such as tolerance factor, new tolerance factor, and deviations of sizes, valences, and electronegativity of metals in the B-sublattice. Despite significant deviations in cation radii, the HEO perovskite structure was still formed, showcasing the role of valence combinations in stabilizing the structure. The achieved mechanical properties, such as acceptable hardness value 5.6 +/- 0.1 GPa and high fracture toughness coefficient 3.47 +/- 0.22 MPa m(1/2) result from high lattice distortions. These findings shed light on the complex behavior and properties of high-entropy oxides, providing insights into their synthesis, structure, and mechanical attributes.

Выполнен анализ изменения параметров элементарных ячеек (ПЭЯ) ортохромитов LnCrO3, Ln = La – Lu,Y, Sc. от эффективных ионных радиусов катионов Ln3+. Показано, что полученные закономерности могут быть описаны уравнениями: a = 69.831RLn3- 223.91RLn2+ 238.76RLn - 79.162, Å ; b =1.5893 RLn + 5.9242, Å , c = 1.8469RLn +3.3691, Å и V= 121.85 RLn + 93.97, Å3, где RLn–эффективный ионный радиус катиона Ln3+, с доверительной вероятностью 0.775, 0.989, 0.998 и 0.990, соответственно. Полученные уравнения предложено использовать для априорного расчета ПЭЯ изовалентных твердых растворов замещения ортохромитов РЗЭ, в том числе высокоэнтропийных ортохромитов через средние значения эффективных радиусов замещающихся катионов Ln3+. Выполнен расчет факторов толерантности для ортохромитов РЗЭ, висмута , таллия и индия. Рассмотрена возможность образования ромбической структуры перовскита, при взаимодействии ортохромитов РЗЭ с не изоструктурными хромитами BiCrO3, ScCrO3.

The catalytic activity of NiAl2O4 spinel and NiO/Al2O3 composite powders were evaluated in the reaction of hydroquinone oxidation. The NiAl2O4 powders were prepared by solution combustion synthesis (SCS) from solutions of nickel and aluminum nitrates, using glycine reductant in stoichiometric ratio (u = 1). The synthesis of NiO/Al2O3 composites powders was carried out under conditions of a glycine excess. All studied samples of spinel and composites exhibit photocatalytic activity. It was determined that the maximum rate of hydroquinone decomposition is achieved for a composite sample with 42.3 % NiO, corresponding to the composition of spinel NiAl2O4; the rate of oxidation involving NiAl2O4 is much lower. However, it was observed a rapid deactivation of composite catalysts, while spinel catalyst showed an almost constant rate of oxidation. (c) 2024 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

The dependence of unit cell parameters (UCPs) of LnCrO3 (Ln = La–Lu, Y) orthochromites on effective ionic radii of Ln3+ cations is analyzed. It is shown that these dependences can be described by the following equations: a = 69.831R_Ln^3-223.91R_Ln^2+238.76R_Ln-79.162 Å; b = 1.5893RLn + 5.9242 Å, c = 1.8469 RLn + 3.3691 Å, and V = 121.85RLn + 93.97 Å3, where RLn is the effective ionic radius of the Ln3+ cation with a confidence probability of 0.775, 0.989, 0.998, and 0.990, respectively. The obtained equations can be use in a priory calculations of the UCPs of isovalent solid substitution solutions of REE orthochromites (including high-entropy ones) using average effective radii of substituted Ln3+ cations. The tolerance factors of REE-, bismuth-, thallium-, and indium orthochromites are calculated. The possibility that an orthorhombic perovskite structure can be formed by the interaction of REE orthochromites with non-isostructural BiCrO3 and ScCrO3 chromites is considered.

The new phosphate vanadates, narrow range solid solutions Ba2.4Mn2.6V1.5P2.5O15 and Ba2.6Mn2.4VP3O15 were synthesized. The structural refinement based on X-ray powder diffraction data showed that these phosphate vanadates are characterized by monoclinic symmetry with space group P21/c, (# 14), Z = 4. The crystal structure of the studied solid solutions can be considered as a monoclinic distortion of the orthorhombic crystal lattice of Sr2.4-хCo2.6+xP3VO15. A rather rare phenomenon was found when barium and manganese (2+) cations share an octahedral site coordinated by oxygen ions.

The new phosphate vanadates, narrow range solid solutions Ba 2.4 Mn 2.6 V 1.5 P 2.5 O 15 and Ba 2.6 Mn 2.4 VP 3 O 15 were synthesized. The structural refinement based on X-ray powder diffraction data showed that these phosphate vanadates are characterized by monoclinic symmetry with space group P 2 1 / c , (# 14), Z = 4. The crystal structure of the studied solid solutions can be considered as a monoclinic distortion of the orthorhombic crystal lattice of Sr 2.4– х Co 2.6+ x P 3 VO 15 . A rather rare phenomenon was found when barium and manganese (2+) cations share an octahedral site coordinated by oxygen ions.

A study into the use of the Solution Combustion Synthesis (SCS) method with glycine and citric acid to synthesize fine powders of multicomponent solid solutions of oxides of rare earth (RE) metals (Nd, Sm, Eu, Gd, Dy, and Ho) for the preparation of ceramic materials is presented. Synthesis parameters of 4-, 5-, and 6-component entropy-stabilized rare earth oxides (REOs) with a C-type cubic structure are determined. The stability of entropy-stabilized oxides (ESOs) with a C-type structure is shown to depend not only on heavy RE metal quantity, but also on the rate of heating/cooling of the samples. The temperature of the polymorphic transformation of C-type REO structures into B-type (monoclinic) or H-type (hexagonal) structural variants can be described by the equation T (°C) = 0.0214Vcr2 − 62.737Vcr + 46390, where Vcr is the unit cell volume of an oxide with a C-type structure regardless of the number of cations in the solid solution. High-temperature thermal analysis up to 1250 °C revealed that dispersed powders, which contain impurities of basic carbonates along with hydroxocarbonates of RE metals and X-ray amorphous carbon formed during SCS reactions, also react with air moisture during storage. The influence of the ESO phase and cationic composition on the morphology, porosity and microhardness of ceramics was studied. Higher-entropy oxides form samples with higher density, microhardness and a smaller size of particle agglomerates.

Lithium aluminate samples were obtained in reactions of solution combustion synthesis (SCS) with various types of fuel (glycine, leucine, and urea) from aluminum and lithium nitrate solutions. The simultaneous thermal analysis (STA) of precursors obtained in conditions of fuel and oxidizer stoichiometry showed the presence of impurities due to incomplete decomposition of initial salts containing carbon fragments of fuel and nitrate groups. An exception was the precursor from the dual-fuel SCS reaction, φ (glycine : urea) = 1 : 3, in which pure γ-LiAlO 2 powder was formed. Replacement of lithium nitrate with lithium carbonate was found to reduce the process temperature and the relative amount of organic fuel. As a result, the content of carbon fragments in the precursor significantly decreased after synthesis.

A comparative analysis of the combustion profiles of SCS of lithium aluminate from a solution of aluminum nitrate and lithium nitrate or carbonate with glycine, leucine, and urea was performed. The influence of the starting solution composition on the maximum combustion temperature and combustion profile was considered. It was found that maximum combustion temperature, 771°C, is observed in case of synthesis of nitrate solution with glycine and urea (1 : 3). The appearance of ballast lithium aminoacetate during syntheses of aluminum nitrate with lithium carbonate and glycine was shown to reduce the maximum combustion temperature by almost 100°C. Replacing lithium nitrate with lithium carbonate decreased the temperature at which γ-LiAlO2 started to form and made it possible to obtain monophasic α-LiAlO2 after heat treatment at 500–550°C.

The polycrystalline samples of BaNi2(V1-xPxO4)2 (x = 0-1) were prepared via a solution combustion synthesis. The study of the crystal structure shows that the substitution of vanadium (5+) cations by smaller phosphorus (5+) cations leads to compression of the [Ni2(V1-xPxO4)2]infinity layers in the ab plane with a decrease in the unit cell volume of BaNi2(V1-xPxO4)2. As a result, the BaO12 polyhedra are elongated along the c axis. The melting point increases monotonically with increasing phosphorus concentration. The linear dependence of the relative elongation (Delta L/L0) of samples on temperature after 500 degrees C becomes S-shaped. The electrical conductivity (sigma) of BaNi2(V1-xPxO4)2 was measured in the range of 300-900 degrees C. Electron transfer in BaNi2(V1-xPxO4)2 established to occur along the Ni-O-Ni chains and is explained by the formation of Ni3+.

The article discusses the results of the synthesis of spinel NiCo2O4 by a new method of hydrothermolysis, as well as methods of precipitation of oxalates and ultrasonic aerosol pyrolysis from aqueous solutions of chlorides and nitrates of nickel and cobalt. The preparation conditions for each synthesis method were selected, the morphology of the obtained samples was considered, the porous structure of the material was studied, and the mesoporosity of the powders was estimated. Single-phase spinel NiCo2O4 was obtained only by precipitation of oxalates; two other methods of synthesis, due to higher temperatures of the processes, lead to the appearance of an impurity of nickel–cobalt double oxide and a decrease in the nickel content in the spinel composition. The nature of the porosity of the materials obtained and the morphology depend on the synthesis method: the mesoporous structure in ultrasonic spray pyrolysis, macroporous structure in hydrothermolysis. The sample obtained by the oxalate precipitation method has the maximum specific surface area of 65.40 ± 0.33 m2/g and a pore volume of 0.409 cm3/g. The samples after hydrothermolysis have the minimum specific surface area of 10.22 ± 0.06 m2/g and a porosity of 0.055 cm3/g. The powders synthesized by ultrasonic spray pyrolysis have intermediate values of these characteristics between the other two methods, 41.68 ± 0.13 m2/g and 0.144 m3/g, respectively.

The polycrystalline orthophosphate Pb0.954(3)Mn2(PO4)(2) was obtained at 830 degrees C in a melt with NaCl. This compound is isostructural to SrMn2(PO4)(2) (structural type Mg-3(PO4)(2)): its triclinic system, a = 8.86706(7) angstrom, b = 9.00697(8) angstrom, c = 10.35293(10) angstrom, alpha = 123.9418(5) , beta = 91.1907(5)angstrom, gamma = 89.8282(7)angstrom, space group P 1, Z = 4 (R-wp = 1.47%, Rp = 1.13%, chi(2) = 2.234, R(F-2) = 3.73%) can be described as a hexagonal close packing of phosphate groups. Octahedral, tetrahedral, and trigonal-bipyramidal voids within the [PO4]-packing provide positions for 8-fold and 10-fold [PbOx] and distorted octahedron [MnO6]. To maintain the valence balance, lead deficiency must be compensated for by a change in the oxidation state of a part of manganese: Pb0.954(3)Mn1.908+2Mn0.092+3(PO4)(2). The IR and Raman spectroscopy of the sample were studied. The energy of the optical band gap E-g determined by the Tauc plot method is 4.2 eV.

Lithium aluminate samples were obtained in SCS reactions with various types of fuel: glycine, leucine, and urea from aluminum and lithium nitrate solutions. The study of the composition of gases released during synchronous thermal analysis of precursors showed the presence of impurities of incomplete decomposition of initial salts containing carbon fragments of fuel and nitrate groups, which oxidize or decompose to CO2 and NO during heating, forming at 850-900°C powders of γ-LiAlO2 with specific surface area 35 – 42 m2/g. An exception is the dual fuel for SCS, glycine: urea = 1:3, in which γ-LiAlO2 powder with a specific surface area of 4.35 m2/g is formed directly during combustion. The replacement of lithium nitrate by lithium carbonate complicates the process of SCS of γ-LiAlO2 due to simultaneous reactions of thermolysis of the products of interaction of glycine or urea with lithium carbonate. As a result, the content of carbon fragments in the precursor significantly decreases after synthesis with glycine, reducing the specific surface of γ-LiAlO2 to 19.89 m2/g after annealing at 900°C, and the presence of lithium carbonate in the reaction with urea makes it possible to obtain monophasic α-LiAlO2 with a specific surface area of 35–42 m2/g after heat treatment of amorphous precursor at 550°C.

The polycrystalline samples of BaNi2(V1−xP x O4)2 (x = 0 – 1) were prepared via a solution combustion synthesis. The study of the crystal structure showed that the substitution of vanadium (5+) cations by smaller phosphorus (5+) cations leads to compression of the [Ni2(V1−xP x O4)2]∞ layers in the ab plane with a decrease in the unit cell volume of BaNi2(V1−xP x O4)2. As a result, the BaO12 polyhedra are elongated along the c axis. The melting point increases monotonically with increasing phosphorus concentration. The linear dependence of the relative elongation (ΔL/L0) of samples on temperature after 500 °C becomes S-shaped. The electrical conductivity (σ) of BaNi2(V1−xP x O4)2 was measured in the range of 300–900 °C. Electron transfer in BaNi2(V1−xP x O4)2 established to occur along the Ni–O–Ni chains and is explained by the formation of Ni3+.

Effect of citric acid (φ = 0.5–1.3) and glycine (φ = 0.5; 0.7–0.9) ratio on the rate of combustion reactions, phase composition, and particle size of CuO x powder obtained from copper nitrate solution under conditions of open and closed reactors has been considered. Modeling of combustion reactions for the synthesis of CuO x has shown that calculations of T max by equation derived for synthesis in combustion reactions are possible also for thermolysis or pyrolysis reactions. Formation, morphology, and dispersity of samples after completion of combustion reactions and thermal treatment at 500°C have been studied by X-ray diffraction and electron microscopy. The characteristics of combustion profiles display transition from bulk combustion mode to self-propagating high-temperature synthesis and further to thermolysis of xerogels when citric acid content increases. It has been found that retardation of redox reaction rate does not decrease CuO loss due to removal of copper within organic volatile components.

Thermal expansion of refractory ceramics CaZrO3, MgAl2O4, La2Zr2O7 and YSZ-12 was studied. The samples of the complex oxides were synthesized by solution combustion synthesis with glycine; the fuel:oxidant ratio was varied depending on the character of redox reaction. The linear thermal expansion coefficient (LTEC) of ceramics was measured on the samples with an initial density 23–52%. The maximal sinterability of 89–92% after 6 h annealing at 1550 °С was demonstrated by La2Zr2O7 and YSZ-12, and the minimal values (78–82%) – by CaZrO3 and MgAl2O4. All materials have close LTEC values, from 9.0 to 9.6·10–6 K–1.

The composition of powders produced in reactions of Solution Combustion Synthesis (SCS) of zinc nitrate with glycine and a mixture of glycine and citric acid has been studied. The precursors formed on completion of solution combustion reactions were established to contain ZnO and up to 7 wt% of carbonaceous fragments due to incomplete oxidation of fuel. The latter are mixtures of residual carbon (0.2-3 wt%) and the fragments of citric acid decomposition, bound carbon, (0.6-4.4 wt%), which are strongly disordered carbon structures in nature, including amorphous ones. The performed thermal analysis of precursors and modeling allow us to suppose that the process of additional oxidation takes place in two stages - at 240-280 degrees C (oxidation of organic fragments) and 410-424 degrees C (oxidation of residual carbon) and is incomplete in character. It was shown that the complete removal of the carbonaceous fragments of organic fuel needs the temperatures close or over 900 degrees C. The best conductivity of ZnO were 1.13.10(-7) and 9.19.10(-8) S/cm after SCS and annealing 650 degrees C, respectively.

The conditions for the production of composites by Solution Combustion Synthesis (SCS) from reaction solutions of aluminum and nickel nitrates of various concentrations with glycine have been studied. The concentration of reaction solutions increases the product yield and the productivity of SCS process. The effect of the presence of Al3+ cations in reaction solutions on the combustion reaction intensity reduction has been established. The SCS precursors contained metallic nickel, nickel oxide and amorphous alumina. The phase composition of the samples changed in the process of annealing: nickel oxidation, crystallization of gamma-Al2O3 (600 degrees C) and formation of NiAl2O4 spinel (600-800 degrees C) were observed. The maximal specific surface area value recorded after annealing at 800 degrees C was 59-63 m(2)/g. In samples obtained with a lower fuel content, gamma-Al2O3 or a mixture of gamma-Al2O3 and NiAl2O4 crystallize on the surface of composite particles. The concentration of NiO on the surface of composites obtained from precursors synthesized from concentrated solutions at phi = 1.4 is close to the nominal composition. (C) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.