New Dion-Jacobson type layered perovskite compounds A'Ln2Ti2NbO10 (A' = Rb, H; Ln = Pr, Nd) were synthesized for the first time. The phase and chemical purity of the compounds were proved by X-ray diffraction (XRD) and EDX. Compounds RbPr2Ti2NbO10 and RbNd2Ti2NbO10 were synthesized using solid-state reactions, whereas HPr2Ti2NbO10.1.5H2O and HNd2Ti2NbO10.2H2O were obtained from Rb-containing phases by ionexchange reactions. Crystal structures of RbPr2Ti2NbO10 (P4/mmm, a = 0.38223 (1) nm, c = 1.51485 (8) nm, Rwp = 3.87%) and RbNd2Ti2NbO10 (P4/mmm, a = 0.38153 (1) nm, c = 1.51200 (6) nm, Rwp = 3.62%) were refined using the Rietveld method. The distortions of polyhedrons in the structures were studied in detail. The thermal behavior of compounds was established using DTA. The ion-exchange products were found to be metastable hydrates. Optical band gap, valence band edge and conduction band edge potentials of obtained compounds were calculated from diffuse reflectance spectroscopy data. Photocatalytic experiment of methylene blue degradation under ultraviolet (UV) light was conducted with ground synthesized compounds. The particle size distributions were measured by laser diffraction before and after grinding. RbNd2Ti2NbO10 showed the highest photocatalytic activity, while HPr2Ti2NbO10.1.5H2O and HNd2Ti2NbO10.2H2O showed none.

Two lead-containing compounds of the Aurivillus family: PbBi2Nb2O9 and PbBi3Ti2NbO12 were synthesized using a conventional high-temperature solid-state (ss) method and ion-exchange (ie) method. The phase and chemical purity of synthesized compounds were confirmed by XRD and EDX, respectively. The second harmonic generation experiment confirmed that all synthesized compounds have a non-centrosymmetric crystal structure. Rietveld refinement of samples prepared by different methods confirmed that ion-exchange and solid-state products share the same crystal structures; however, indirect evidence for different distributions of Pb/Bi between crystallographic positions was observed. Phase transitions, corresponding to the Curie temperatures were detected using high-temperature XRD. Thermal expansion of ion-exchange reaction products was studied in the temperature range of 298-1273 K. The optical band gap, electronegativity, valence band (EVB), and conduction band (ECB) potentials of materials were calculated from UV-vis spectroscopy data. Both PbBi2Nb2O9 (ss) and PbBi2Nb2O9 (ie) can be used for the decomposition of organic molecules under visible light, while PbBi3Ti2NbO12 (ss) and PbBi3Ti2NbO12 (ie) can work only under UV light irradiation due to their wider band gaps.

The heat capacity of layered perovskite-like oxide Sr3Fe2O7 was measured for the first time by precision adiabatic vacuum calorimetry over the temperature range of (6-305) K and by differential scanning calorimetry in the range from 300 K to 420 K. The standard thermodynamic functions of the compound were evaluated from the experimental heat capacity temperature dependences over the range of (0-420) K. The phase transitions of the compound were studied by means of X-ray diffraction and differential scanning calorimetry. The main regularities of the thermal expansion of Sr3Fe2O7 are revealed. The mechanisms of the phase transitions at 120 K and 366 K are suggested. More significant structural changes were observed for metal-insulator transition. All transformations occur within the tetragonal symmetry of the unit cell. (C) 2020 Elsevier Ltd.

Thermodynamic properties of Dion-Jacobson type layered perovskite phase KCa2NaNb4O13 were studied. Thermal expansion behaviour and phase transition of the compound were established using high-temperature X-ray diffraction (HTXRD). Temperature dependence of heat capacity of KCa2NaNb4O13 was measured by precision adiabatic vacuum calorimetry. Thermodynamic functions of the phase, namely, the heat capacity, enthalpy H degrees(T)-H degrees(0), entropy S degrees(T)-S degrees(0) and Gibbs function G degrees(T)-H degrees(0) have been determined for the range from T -> 0 K to 345 K based on the experimental data. (C) 2019 Elsevier Ltd.

Isodimorphism for two Aurivillius phases BaBi4Ti4O15 and CaBi4Ti4O15 with different symmetry was studied. Synthesis techniques have been optimized and solid solution with the composition Ba1-xCaxBi4Ti4O15 (x - molar part of the component, x = 0, 0.25, 0.5, 0.75, 1) have been prepared. The structure of the compounds has been studied using X-ray diffraction and Raman spectroscopy. It was found that solid solutions with tetragonal and orthorhombic symmetry were formed in the range of 0 < x < 0.75 and at x >= 0.75, respectively. The basic laws of thermal expansion for the binary system BaBi4Ti4O15-CaBi4Ti4O15 have been established.

We demonstrate the up-conversion of Tm:LiYF4 infrared (IR) laser radiation with 1908-nm wavelength into visible light with a spectral maximum at 650 nm by ceramics with a composition of (100 − x)TeO2−xBaF2 − 1 wt % HoF3−yYbF3, where x = 20, 30, or 40 mol % and y = 0 or 0.5 wt %. The samples of 60TeO2−40BaF2 − 1 wt % HoF3 − 0.5 wt % YbF3 exhibited anti-Stokes luminescence at a threshold radiation power density of 1.0−1.5 W cm−2.

The compounds Bi2MO6 (m = 1), Bi2WO6 (m = 1), Bi3NbTiO9 (m = 2), Bi4Ti3O12 (m = 3) and CaBi4Ti4O15 (m = 4) (Aurivillius phases with the general formula A(m-1)Bi(2)BmO(3m+3)) have been synthesized by solid state reaction method. Using the high-temperature X-ray diffraction, the phase transition and melting temperatures have been determined for these compounds and their thermal expansion coefficients have been calculated. It has been established that composition and structure of Aurivillius phases have significant influence on the Curie temperature. We have also measured room temperature Raman and infrared spectra, and all observed bands have been assigned to respective motions of atoms in the unit cell. The spectra of the synthesized Auriviliius phases are in good agreement with reported in literature results of the lattice dynamics calculations. We also compare and discuss how the spectra change with increasing thickness of the perovskite-like layer. (C) 2017 Elsevier B.V. All rights reserved.

We demonstrate the up-conversion of Tm:LiYF 4 infrared (IR) laser radiation with 1908-nm wavelength into visible light with a spectral maximum at 650 nm by ceramics with a composition of (100 − x )TeO 2 − x BaF 2 − 1 wt % HoF 3 − y YbF 3 , where x = 20, 30, or 40 mol % and y = 0 or 0.5 wt %. The samples of 60TeO 2 −40BaF 2 − 1 wt % HoF 3 − 0.5 wt % YbF 3 exhibited anti-Stokes luminescence at a threshold radiation power density of 1.0−1.5 W cm −2 .

Показано преобразование ИК-излучения лазера Tm : LiYF4 с длиной волны 1908 nm в видимый свет с максимумом 650 nm керамикой состава (100-x)TeO2-xBaF2-1 wt% HoF3-yYbF3, где x=20,30,40 mol.%, y=0 или 0.5 wt%. На образцах 60TeO2-40BaF2-1 wt% HoF3-0.5 wt% YbF3 наблюдалась антистоксовая люминесценция при пороговой плотности мощности излучения 1.0-1.5 W · cm-2. DOI: 10.21883/PJTF.2017.14.44829.16771

The temperature dependence of heat capacity of Bi4Ti3O12 has been measured for the first time in the range from 7 to 346 K by precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity, enthalpy H o(T) − H o(0), entropy S o(T) − S o(0), and Gibbs function G o(T) − H o(0), in the range from T → 0 to 346 K. The structure of Bi4Ti3O12 is refined by the Rietveld method (space group Fmmm, Z = 4) at temperatures of 173, 273, 373, 473 K. Thermal deformation model is proposed on the basis of structural data.

Compounds of the composition M kMn2O4 (M k Li, Cu, Zn, Cd) which crystallize in the mineral spinel structure type have been synthesized by high-temperature solid-phase reactions. The behavior of the compounds in the temperature range of 298-1473 K was investigated using a differential scanning calorimeter. The temperature dependencies of unit cell parameters and phase transitions were investigated using high-temperature and low-temperature x-ray diffraction methods and the thermal expansion coefficients were determined for four spinel structure compounds.

The compounds Bi2MoO6 (m = 1), Bi3NbTiO9 (m = 2), Bi4Ti3O12 (m = 3), BaBi4Ti4O15 (m = 4), and Ba2Bi4Ti5O18 (m = 5) (Aurivillius phases with the general formula A m − 1Bi2B m O3m + 3) have been synthesized by solid-state reactions. Using differential scanning calorimetry and high-temperature X-ray diffraction, we have studied their phase transitions and determined their thermal expansion coefficients.

Методом реакций в твердой фазе синтезированы соединения Bi2MoO6 (m = 1), Bi3NbTiO9 (m = 2), Bi4Ti3O12 (m = 3), BaBi4Ti4O15 (m = 4) и Ba2Bi4Ti5O18 (m = 5), которые относятся к фазам Ауривиллиуса с общей формулой Аm - 1Bi2BmO3m + 3. Методами дифференциальной сканирующей калориметрии и высокотемпературной рентгенографии изучены фазовые переходы и определены коэффициенты теплового расширения соединений.

Compounds of the composition Co xNi 1-xAl 2O 4 (x = 0, 0.25, 0.5, 0.75, 1) were synthesized by high-temperature reactions in the solid phase at 1200°C. The compounds crystallize in the mineral spinel structure type. The crystal structures of the individual compounds and solid solution with equimolar content of components were refined by the Rietveld method (space group Fd3m). The temperature dependencies of unit cell parameters were investigated using a high-temperature XRD method. The thermal expansion coefficients of five compounds with the structure of spinel were determined.

Compounds with the general formula CaLn4(SiO4)3O (Ln = Pr, Sm, Eu), belonging to the apatite class, have been prepared by solid-state reactions and have been studied at high temperatures by high-temperature X-ray diffraction and differential scanning calorimetry. The results demonstrate that the volume expansivity of these apatites and its temperature coefficient are determined by the ionic radius of the lanthanides.