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Methods for the synthesis of LaNi1/3Sb5/3O6 with a rosiaite structure have been developed using citrate method and coprecipitation followed by annealing. The influence of synthesis conditions on the morphology of the samples has been demonstrated. A comparative analysis of the catalytic properties of LaNi1/3Sb5/3O6 synthesized by various methods, in the reaction of CO oxidation has been carried out. The catalyst synthesized by the citrate method demonstrated the greatest efficiency and stability (the temperature of 90% CO conversion was T90 = 336°C). The LaNi1/3Sb5/3O6 surface was studied before and after catalysis by in situ diffuse reflectance IR spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed O2 desorption. It has been shown that the catalytic oxidation of CO on the LaNi1/3Sb5/3O6 surface proceeds according to the Mars–van Krevelen mechanism and is accompanied by redox Sb3+ ↔ Sb5+ processes. It has been established that no contamination of the sample surface occurs during the catalysis process. [ABSTRACT FROM AUTHOR]

Mg-containing solid solutions based on Y2FeTaO7 and formed by various mechanisms of heterovalent substitution were synthesized and had the following compositions: Y2Fe0.55Mg0.3Ta1.15O7, Y2Fe0.625Mg0.3Ta1.075O7, Y2Fe0.7Mg0.3TaO7, Y2Fe0.7Mg0.2Ta1.1O7, Y2Fe0.85Mg0.15TaO7, Y1.85Mg0.15Fe0.925Ta1.075O7, and Y1.85Mg0.15FeTaO7. It was shown that all synthesized solid solutions have a pyrochlore-like layered structure (space group P3121), in which Fe3+ ions are distributed over three structural positions. The magnetic properties of these solid solutions are due to the presence of a small ferromagnetic component in a predominantly antiferromagnetic system and characterize a ferrimagnet or a canted antiferromagnet with the Néel transition at the Néel temperature TN above room temperature. According to the data of magnetic measurements, two magnetic phase transitions to the ordered phase occur in all the studied samples. Along with the TN transition, in weak magnetic fields and below TN, there is a second transition, which is most likely due to a spin reorientation of the Morin type. The existence of magnetic ordering at room temperature in one magnetic sublattice or an internal magnetic field (Hin) was confirmed by Mössbauer spectroscopy. [ABSTRACT FROM AUTHOR]

Highly efficient and stable catalysts PdO/LnFe0.5Sb1.5O6, Ln – La, Ce, Pr, Nd, Sm, promising in the reaction of complete methane oxidation have been obtained using the deposition–precipitation method. The catalysts contain complex oxides, which crystallize in a rosiaite-type structure (sp.gr. P31m). These oxides have been used for the first time as support. The catalysts samples are characterized by a uniform distribution of PdOx particles the average size of which is 13 nm. The 90% methane conversion temperature, T90, for PdO/LnFe0.5Sb1.5O6, which were obtained without catalyst prе-activation, lie in the range of 367–382°C and does not depend on the REE ion radius. Catalytic activity dependence on the amount of supported active component is studied and the optimal content in terms of metal equal to 1 wt % Pd is found. The correlations between the synthesis conditions and catalytic activity of PdO/LnFe0.5Sb1.5O6 are established. The catalyst PdO/LaFe0.5Sb1.5O6 with the best catalytic characteristics is studied by X-ray photoelectron spectroscopy, IR spectroscopy, and O2-TPD. According to the XPS-data Pd oxidation state before and after catalytic reaction is Pd2+ in PdO species. The promoting role of the oxide support with rosiaite structure is shown and the mechanism of CH4 complete oxidation on PdO/LnFe0.5Sb1.5O6 is proposed. [ABSTRACT FROM AUTHOR]

The possibility to prepare transparent scintillation composite materials based on SiO2 aerogels with Bi4Ge3O12 filler has been shown for the first time. Effect of gelation catalysts (HF and ammonium hydroxide), solvents (methanol, isopropanol, acetone, methyl cellosolve, and methyl lactate), and supercritical drying conditions (CO2, alcohols) on transparency and textural properties of SiO2 aerogels has been studied. A procedure for Bi4Ge3O12 dispersing in transparent aerogels based on SiO2 has been developed and composite materials containing Bi4Ge3O12 of different morphology have been synthesized. The study of scintillation properties of the prepared samples showed their complete correspondence to the properties of Bi4Ge3O12 single crystals [ABSTRACT FROM AUTHOR]

An isothermal section of the Sm2O3–Fe2O3–Ta2O5 system was constructed in the subsolidus region at 1200°C. A region of the Sm2 – xFe1 + xTaO7 solid solution with the cubic pyrochlore structure (space group Fd m) was found. A study of the polythermal section of the system along the Sm2 – xFe1 + xTaO7 section showed that the previously known compound Sm2FeTaO7 (R) with the structure of rhombohedrally distorted pyrochlore (space group R ) is stable in the temperature range <1200°C. With increasing temperature, Sm2FeTaO7 (R) becomes an intermediate phase, and a reversible transition to the cubic pyrochlore (C) phase is observed. The kinetic hindrances of the transition R → Fd m determine the short-term stability of the R phase at temperatures exceeding the phase transition temperature by 200°C. It was established that cubic pyrochlore exists as the Sm2 – xFe1 + xTaO7 solid solution in the ranges x = 0–0.4 at t ≥ 1200°C and x = 0.15–0.4 at lower temperatures. Two independent methods—Mössbauer spectroscopy and XANES—detected that the rhombohedral phase contains not only Fe3+ ions but also Fe4+ ions. The magnetic properties were studied, and it was shown that both the R phase and the C phase at T < 10 K undergo two magnetic transitions of different types: an antiferromagnetic transition observed in a strong magnetic field at 7.2 and 5.5 K, respectively, and a transition to the spin glass state in a field of 100 Oe at 8.4 and 4.8 K, respectively. It was determined that the spin glass state coexists with short-range antiferromagnetic interactions until 2.3 K. Despite the fact that the R and C phases formally have geometrically frustrated magnetic sublattices, the experimental data showed that frustration manifests itself only in the R phase. [ABSTRACT FROM AUTHOR]

The optical properties of CsSnI3 perovskite thin films were investigated. The thin films were obtained from CsI and SnI2 precursors (special-purity grade, 99.999%, 5N), and also SnI2 (99%) by spin-coating from the corresponding solutions. The films were studied by X-ray powder diffraction analysis, scanning electron microscopy, and optical spectroscopy. It was shown that impurities in the initial components affect the optical properties of the obtained material: the absorption coefficient of the perovskite films synthesized from the special-purity grade SnI2 is higher than those of the films produced from 99% SnI2: 4 × 105 cm–1 and 6 × 105 cm–1, respectively. The optical band gap was estimated using the Tauc and Kubelka–Munk models. [ABSTRACT FROM AUTHOR]

Ln2CrTaO7 (Ln = Sm, Gd, Y) pyrochlores are synthesized by the co-precipitation with subsequent annealing. The effect of the precursor composition ((NH4)2Cr2O7, Cr(NO3)3, and CrCl3) on the precipitates reactivity and product microstructure was studied. Samples with an average particle size of 200 nm for Y2CrTaO7, 450 nm for Gd2CrTaO7 and 600 nm for Sm2CrTaO7 were used to study thermodynamic properties. The temperature dependences of heat capacity were measured by the adiabatic calorimetry (13–346.16 K) method and the ratio method using DSC measurements (330–1300 K). The thermodynamic functions of Ln2CrTaO7 compounds were calculated. The absence of polymorphic transitions up to a temperature of 1450°C for all studied compounds is shown. [ABSTRACT FROM AUTHOR]

Efficient method for the directed synthesis of ZrO2–Er2O3 luminescent material in nanocrystalline state has been developed. Monodisperse samples of cubic modification with particle size from 5 to 71 nm depending on synthesis conditions have been synthesized. Luminescence spectra due to 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 transitions of Er3+ ions have been registered upon their excitation by 532-nm radiation. Upconversion luminescence spectra due to 2H11/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 transitions have been registered on excitation to level 4I13/2 of Er3+ ions by 1550-nm radiation. [ABSTRACT FROM AUTHOR]

A comparative analysis has been made for the dielectric and electrorheological properties of suspensions of highly dispersed powders of bismuth ferrites BiFeO3 and Bi2Fe4O9 in polydimethylsiloxane PMS-300. Dielectric characteristics (dielectric constant, dielectric loss tangent) for the suspensions in frequency range 2.5–106 Hz have been determined and non-Debye character of relaxation processes in these systems has been revealed. The measured values of dielectric constant for the disperse bismuth ferrites at zero and infinite frequency (ε0 and ε∞) are 150 and 59 for BiFeO3, 22 000 and 14 for Bi2Fe4O9, respectively. Electrorheological properties of bismuth ferrite suspensions in static electric field (up to 5 kV) in tension, compression, and shear modes have been analyzed. It has been found that the values of electrorheological effect for BiFeO3 suspensions in polydimethylsiloxane PMS-300 are small even at high concentrations of disperse phase (60 wt %). On the contrary, the suspensions of highly disperse Bi2Fe4O9 exhibit distinct electrorheological effect. For 80 wt % Bi2Fe4O9 suspension, the tensile yield point reached ~7 kPa in electric field of 5 kV, while compressive stress was 12 kPa. [ABSTRACT FROM AUTHOR]