Gadolinium ferrochromites were successfully synthesized as continuous solid solutions in the GdFeO3 - GdCrO3 system via solid-state reaction. Structural and microstructure analyses revealed the formation of an orthorhombic perovskite-type phase with isometric chain-like grains. SEM data demonstrated a systematic decrease in the average grain size, from similar to 9.0 mu m to similar to 2.0 mu m, as the Cr content increased. The thermal properties, including thermal diffusivity and thermal conductivity, were investigated using the laser-flash diffusivity method. Thermal diffusivity was observed to decrease with increasing Cr substitution, consistent with enhanced phonon scattering induced by finer grains and increased porosity. Compositions with x = 0.50 and 0.77, sintered at 1400 degrees C for 24 h, exhibited optimal thermal insulation properties, characterized by porosity levels of 44-48 % and thermal conductivities of 0.6-0.7 W/(m & lowast;K) at room temperature. These findings demonstrate that the microstructure and thermal properties of GdFe1-xCrxO3 oxides can be tuned through Cr doping, making them promising candidates for thermal insulation applications in high-temperature conditions.

Herein, we present a novel approach for the preparation of orthoferrite solid solution through direct mechanochemical synthesis and compare them with samples synthesized by the conventional solid-state method. Results obtained show the formation of an orthorhombic perovskite structure of GdFe1-xCrxO3 during ball milling at 500 rpm for 4 h. A study of the formation mechanism reveals that after 15 min of mechanical activation, GdFeO3 is the first to form, and subsequent mechanical treatment for 4 h promotes the introduction of chromium into the crystalline structure of GdFeO3. The samples synthesized by mechanochemical activation demonstrated the strongest photocatalytic activity for the degradation of rhodamine-B (RhB) dye under simulated solar light irradiation of intensity (15 mW/cm2). The photodecomposition rate of RhB was improved about 6 times using samples obtained by mechanochemical synthesis compared to orthoferrite samples synthesized by the solid-state method. This enhanced photocatalytic activity was demonstrated to originate from superoxide O 2 center dot- radicals and singlet oxygen 1 O 2 , which demonstrated synergetic effects with activated center dot OH radicals via a Fenton-like reaction. These findings underscore the potential of mechanochemical synthesis for advanced photocatalytic materials and emphasize the importance of understanding synthesis-route-dependent properties to harness the full potential of rare earth orthoferrites.

The Gd2O3 – GdSrFeO4 pseudo-binary phase diagram is presented for the first time. The liquidus and eutectic temperatures, metatectic points of the Gd2O3 transformations in the Gd2O3 – GdSrFeO4 section were defined using the Schröder–Le Chatelier equation, neglecting the effect of the isobaric heat capacity. The calculations were based on experimental data on the melting points of the end-members and the eutectic composition. From the results of phase relationships studies (subsolidus and high temperature region including literature data as well) and the above approach the Gd2O3–GdSrFeO4 pseudo-binary phase diagram in the temperature range 1400–2410 °C in air was constructed.It was shown that GdSrFeO4 of the K2NiF4- type is stable from 1100°С to a congruent melting temperature of 1560°С in air. The Gd2O3 – GdSrFeO4 system is eutectic with no intermediate compounds.

The results of a study of the GdAlO3–SrO section, which is one of the internal sections of the Gd2O3–SrO–Al2O3 ternary system, are presented. In the GdAlO3–SrO section three triple compounds, Gd2SrAl2O7, GdSrAlO4, and GdSr2AlO5, crystallizing in the tetragonal system, are synthesized. The data on the mechanism of their solid-phase formation are systematized. The results of the thermal stability of perovskite-like phases in the GdAlO3–SrO system are presented in a wide temperature range of 1100–1800°C in air. The congruent character of the melting of Gd2SrAl2O7, GdSrAlO4, and GdSr2AlO5 complex oxides is established and their melting temperatures are determined.

The lack of data systematization on the coexistence and stability of compounds formed in the SrO – GdO1.5 – FeO1.5 system at temperatures above 1100°C determines the interest in a more detailed study of this system. The research was focused on studying the stability of phases formed in the pseudobinary section (1-х)GdFeO3 – хSrO in the temperature range 1200- 1400°C in air. The interaction of components in the SrO – GdO1.5 – FeO1.5 system was studied by the method of annealing and quenching followed by physicochemical analysis. The phase composition and sequence of phase transformations were characterized by powder X-ray diffraction. Phase relations results in the SrO – GdO1.5 – FeO1.5 system in air were systematized. The formation of three complex perovskite-like oxides GdSr2FeO5, GdSrFeO4, Gd2SrFe2O7, located on the GdFeO3 – SrO binary section was established. Information on interplanar distances and reflection intensities of the GdSr2FeO5 compound has been supplemented and the existence of a miscibility gap for Gd1-xSrxFeO3-α solid solutions existing in the range 0.05≤x≤0.51 at 1400°C has been shown. Data on thermal stability of complex gadolinium ferrites based on GdO1.5 – SrO – FeO1.5 system has been expanded.

Continuous solid solutions of two-layer (La 1 – x Ho x ) 2 SrAl 2 O 7 aluninates, which are Ruddlesden–Popper phases, have been found to exist in the La 2 SrAl 2 O 7 –Ho 2 SrAl 2 O 7 system at temperatures above 1515°С. The (La 1 – x Ho x ) 2 SrAl 2 O 7 complex aluminates crystallize in tetragonal crystal system (space group I 4/ mmm ). A phase transformation scheme has been proposed for the La 2 SrAl 2 O 7 –Ho 2 SrAl 2 O 7 system with the unlimited mutual solubility of the components at high temperatures and with a decomposition area below the critical temperature Т cr = 1515°С.

Continuous solid solutions of two-layer (La1 – xHox)2SrAl2O7 aluninates, which are Ruddlesden–Popper phases, have been found to exist in the La2SrAl2O7–Ho2SrAl2O7 system at temperatures above 1515°С. The (La1 – xHox)2SrAl2O7 complex aluminates crystallize in tetragonal crystal system (space group I4/mmm). A phase transformation scheme has been proposed for the La2SrAl2O7–Ho2SrAl2O7 system with the unlimited mutual solubility of the components at high temperatures and with a decomposition area below the critical temperature Тcr = 1515°С.

The phase relations in the subsolidus region of the GdO 1.5 –FeO 1.5 –SrO system are studied at 1200–1400°C in air. The formation of three complex perovskite-like oxides is shown: GdSr 2 FeO 5 , GdSrFeO 4 , and Gd 2 SrFe 2 O 7 , crystallizing in the tetragonal syngony. These compounds lie on the binary cross section of GdFeO 3 –SrO of the GdO 1.5 –FeO 1.5 –SrO system, of which the last two oxides form the homologous series Gd n SrFe n O 3 n + 1 , where n = 1, 2. For the first time in conditions of the solid phase synthesis of the thermal treatment of a mixture of initial oxides of gadolinium, iron (III), and strontium carbonate at 1200°C for 5 h yielded the compound GdSr 2 FeO 5 , crystallizing in the Cs 3 CoCl 5 (sp. gr. I4/mcm) structural type. The mechanism of its formation is determined: the rate-limiting step is the reaction of the interaction of two Gd 2 SrO 4 and Sr 3 Fe 2 O 6 oxides, crystallizing into close structural types. It is shown that ferrite GdSr 2 FeO 5 is stable in the range of investigated temperatures of 1200 to 1400°C in air.

This work provides data on strategies for single GdSrFeO4 phase solid state synthesis. Earlier works have shown that under the solid-state synthesis conditions, the GdSrFeO4 preparation is hampered by the formation of non-target product: Gd2SrFe2O7. This work approach led to the solid-phase synthesis GdSrFeO4 scheme change. GdSrFeO4 was characterized by X-Ray, scanning electron microscopy/energy dispersive X-ray spectroscopy, dilatometry and complex thermal analysis methods. GdSrFeO4 is stable in the wide range of studied temperatures 40–1,400°C in air. The sintering start temperature was determined to be 985°C. GdSrFeO4 has a thermal expansion coefficient of 30 × 10−6 K−1. The thermal stability is excellent for further investigation and potential for application of the materials as SOFC, for example. The study of catalytic stability of the obtained GdSrFeO4 is to be a subject of future work as well.

We report on the analysis of the structural properties of nanocrystalline neodymium ferrite produced by the solution combustion method. The Raman spectrum and X-ray diffraction patterns were measured and analyzed by comparison with the literature data. The Raman spectrum demonstrated the superposition of bands assigned to two substances, namely nanocrystalline neodymium ferrite and traces of iron oxide as hematite. The achieved results lend credence to the idea that particles with a crystalline neodymium ferrite core encased in hematite-like iron oxide scatter light.

Layered perovskite-like oxides with the structure of two-layer Ruddlesden–Popper phases of the composition Nd2Sr(Al1 – xFex)2O7 (0 < х < 1) have been obtained for the first time. It is shown that the determining parameter in the solid-phase synthesis of Nd2Sr(Al1 – xFex)2O7 is the melting point of the surface (two-dimensional non-autonomous) phase, which activates mass transfer processes and ensures a high rate of the chemical reaction. The analysis of stability and phase transformations of Nd2Sr(Al1 – xFex)2O7 two layer phases in the temperature range of 1100–1900°C has been carried out. It is shown that the extreme compounds of the Nd2SrAl2O7–Nd2SrFe2O7 system under consideration are formed according to a single mechanism and melt incongruently with the formation of phases with the perovskite structure. It has been experimentally established that solid solutions Nd2Sr(Al1 – xFex)2O7 are stable in the temperature range from 1400°С to their melting points.

The combination of technically useful physicochemical properties allows the use of materials based on lutetium aluminates as lasers and scintillators in calorimetry in high energy physics and in medical diagnostics. Synthesis of single crystals based on lutetium aluminates LuAlO3 and Lu3Al5O12 is carried out in inert, inert-reducing media, and in vacuum. In this study, the stability of lutetium aluminates in the Lu2O3–Al2O3 systems is studied for the first time by differential thermal analysis up to 2100°C followed by X-ray phase analysis in a helium atmosphere and dynamic vacuum. A comparative analysis of the behavior of lutetium aluminates with the previously obtained data in air and in an argon-hydrogen atmosphere is carried out. We use single crystals of LuAlO3 (structural type of perovskite) and Lu3Al5O12 (structural type of garnet) obtained by the Bridgman method. Lu4Al2O9 polycrystals (monoclinic structure) are synthesized by melt quenching.

Layered perovskite-like oxides with the structure of two-layer Ruddlesden–Popper phases of the composition Nd 2 Sr(Al 1 – x Fe x ) 2 O 7 (0 < х < 1) have been obtained for the first time. It is shown that the determining parameter in the solid-phase synthesis of Nd 2 Sr(Al 1 – x Fe x ) 2 O 7 is the melting point of the surface (two-dimensional non-autonomous) phase, which activates mass transfer processes and ensures a high rate of the chemical reaction. The analysis of stability and phase transformations of Nd 2 Sr(Al 1 – x Fe x ) 2 O 7 two layer phases in the temperature range of 1100–1900°C has been carried out. It is shown that the extreme compounds of the Nd 2 SrAl 2 O 7 –Nd 2 SrFe 2 O 7 system under consideration are formed according to a single mechanism and melt incongruently with the formation of phases with the perovskite structure. It has been experimentally established that solid solutions Nd 2 Sr(Al 1 – x Fe x ) 2 O 7 are stable in the temperature range from 1400°С to their melting points.

In this paper, the achievements, problems and prospects of creating personalized energy systems based on nanostructured materials are analysed.Various concepts of developing methods and ways of personalized energy provision for autonomous human survival in remote natural habitat, emergency situations of natural disasters and technogenic catastrophes when centralized power supply is unavailable or in an effort to reduce the economic and environmental costs of remote energy production and transportation are also considered.The possibilities and limitations of using traditional and renewable alternative energy sources, processes and devices for extracting, storing and converting their energy into the necessary consumer forms due to fundamental physical laws are discussed as well.The article covers the new nanostructured materials with special functional properties for personalized energy systems development.The mechanisms for formation of the required nanostructures in synthesized materials, especially those with a high content of fractal interfacial formations, are considered as well as methods for studying their structural and phase characteristics that determine the achievability of the specified parameters of model converters and energy storage devices.

Multiphase ceramics are synthesized based on layered calcium cobaltite with a different cobalt oxide content by solid state synthesis followed by two-stage sintering. The phase composition is established, and the microstructure, electrical conductivity, and thermal electromotive force are investigated. The effect that the cation and phase compositions of ceramics have on its carrier transport properties and thermoelectric properties is established. The highest value for the power factor P is observed for multiphase ceramics with the composition Ca3Co3.4O9 + δ (0.7Ca3Co4O9 + δ + 0.3Ca3Co2O6), which is 265 μW/(m K2) at a temperature of 1100 K. This value is 20% higher than that for the Ca3Co4O9 + δ sample (P1100 = 218 μW/(m K2)) and exceeds the power factor value for low-density Ca3Co4O9 + δ ceramics prepared by the conventional solid state synthesis by a factor of 2.65.

NdCoO3 nanocrystals formed via glycine–nitrate combustion method followed by heat treatment has been systematically studied. Formation of NdCoO3 nanocrystals with minimal size of 7–10 nm from X-ray amorphous combustion products has been elucidated to be a very rapid process, occurring at the temperature of 550–600 °C for 5–30 min. The comparison of the minimum sizes of NdCoO3 crystallites obtained from the offered empirical relation dmin = ℓunit cell·N (where N is 7–12 and ℓunit cell is elementary cell parameter) and the data determined on the basis of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed good correlation. The existence of special nanoporous microstructure and spatial limitations prevent NdCoO3 particle growth. The kinetic equation based on Avrami–Erofeev nucleation model was offered to be correlated well with experimental data of fractional conversion (α) versus isothermal time (τ). The apparent activation energy (Ea = (338 ± 32) kJ) of formation of NdCoO3 nanocrystals from X-ray amorphous combustion products obtained in excess of oxidant followed by heat treatment at 550–600 °C was determined.

Nanocrystals of Nd1-xBixFeO3 were produced during the process of combustion of the glycine-nitrate with precursors together with an excess amount of the oxidizing agent. X-ray diffraction patterns and Raman spectra were measured for investigation of the structure of the synthesized material. Hidden periodicities were extracted in the Raman spectra, using the example of two compounds with x = 0 and x = 0.2, correspondingly. In comparison with theory, the analysis showed that the distribution of the inverse periods revealed from the experiment results in the appearance of two narrow peaks common for both samples with maximums 0.014 and 0.01 cm (70 and 100 cm(-1)). The discovered effect is analyzed with the model of a combination of Raman-active oscillations from the nanoscale inelastic light scatterers with different shapes.