Erbium gallium titanate was prepared by solid-phase synthesis via the sequential calcination of precursor oxides in an air atmosphere at 1273 and 1573 K. The crystal structure of ErGaTi2O7 was characterized by full-profile analysis for the X-ray diffraction pattern of the synthesized powder sample as follows: space group Pcnb, a = 9.77326(15) Å, b = 13.5170(2) Å, c = 7.33189(11) Å, V = 918.58(3) Å3, ρ = 6.10 g/cm3. The high-temperature heat capacity of erbium gallium titanate was measured by differential scanning calorimetry within a temperature range of 320–1000 K. Based on these data, the basic thermodynamic functions of ErGaTi2O7 were calculated.

Titanate GdGaTi2O7 has been obtained from the initial oxides Gd2O3, Ga2O3, and TiO2 by the solid-state synthesis via annealing in air at temperatures of 1273 and 1573 K. The crystal structure of the titanate has been refined by X-ray diffraction. The high-temperature (320–1000 K) heat capacity of the compound has been measured by differential scanning calorimetry. Based on the experimental dependence Cp = f(T), the main thermodynamic functions of the titanate have been calculated.

— The DyGaTi 2 O 7 and EuGaTi 2 O 7 titanates have been prepared by solid-state reactions in a starting mixture of Dy 2 O 3 (Eu 2 O 3 ), Ga 2 O 3 , and TiO 2 via firing in air at temperatures of 1273 and 1573 K, and their crystal structure has been studied by X-ray diffraction. Their high-temperature heat capacity (350–1000 K) has been determined by differential scanning calorimetry. The C p ( T ) experimental data have been used to calculate the thermodynamic functions of the titanates.

Твердофазным синтезом из исходных оксидов Gd2O3, Ga2O3 и TiO2 обжигом на воздухе при температурах 1273 и 1573 K получен титанат GdGaTi2O7. Методом рентгеновской дифракции уточнена его кристаллическая структура. Высокотемпературная теплоемкость (320-1000 K) этого соединения измерена методом дифференциальной сканирующей калориметрии. На основании экспериментальной зависимости C_p=f(T) рассчитаны его основные термодинамические функции. Ключевые слова: титанаты редкоземельных элементов, твердофазный синтез, высокотемпературная теплоемкость, термодинамические функции.

Bi4–xNdxTi3O12 (x = 0.4, 0.8, 1.2, 1.6) bismuth neodymium titanate solid solutions have been prepared by solid-state reactions, via firing of mixtures of their constituent oxides in air at temperatures from 1003 to 1323 K. The crystal structure of the synthesized phases has been determined by X-ray diffraction. The results demonstrate that increasing the neodymium concentration leads to a morphotropic phase transition from the orthorhombic structure (sp. gr. B2cb) of the parent phase Bi4Ti3O12 (which persists at x = 0.4 and 0.8) to a tetragonal structure (sp. gr. P42/ncm) at x = 1.2 and 1.6. The heat capacity of the synthesized bismuth neodymium titanate samples has been determined by differential scanning calorimetry in the temperature range 320–1000 K. The Cp(T) curves of the Bi4 – xNdxTi3O12 samples with x = 0.4 and 0.8 have been shown to have extrema due to their ferroelectric phase transition.

— Bi 4– x Pr x Ti 3 O 12 ( x = 0.4, 0.8, 1.2, 1.6) solid solutions have been prepared by solid-state reactions, via multistep firing of stoichiometric mixtures of their constituent oxides in air at temperatures from 1003 to 1323 K. Their crystal structure has been determined using X-ray diffraction, and their luminescence spectra have been measured at room temperature. High-temperature heat capacity of polycrystalline substituted bismuth titanate samples has been determined by differential scanning calorimetry. The C p ( T ) curves of the solid solutions with x = 0.4 and 0.8 have extrema related to phase transitions. Experimental data have been used to calculate the main thermodynamic functions of the solid solutions.

Abstract The Y_0.4Bi_0.6VO_4 and Y_0.6Bi_0.4VO_4 solid solutions two-phase at x _Bi = 0.95, 0.90, and 0.80 have been formed by the solid-phase synthesis from the initial Y_2O_3, Bi_2O_3, and V_2O_5 oxides burned in air at a temperature of 1173 K for 200 h and their high-temperature heat capacity has been measured in the range of 350–1000 K by differential scanning calorimetry. The thermodynamic properties of the solution solutions have been calculated using the data obtained.

— The Bi 12 TiO 20 , Bi 4 Ti 3 O 12 , and Bi 2 Ti 4 O 11 bismuth titanates have been prepared by solid-state reactions, via multistep firing of stoichiometric mixtures of their constituent oxides in air at temperatures from 1003 to 1273 K (Bi 12 TiO 20 , to 1123 K). The heat capacity of polycrystalline samples of the synthesized compounds has been determined by differential scanning calorimetry in the temperature range 330–1050 K. The C p ( T ) curves of Bi 4 Ti 3 O 12 and Bi 2 Ti 4 O 11 show peaks at temperatures of 943 and 509 K, respectively, due to ferroelectric phase transitions. The experimental data have been used to evaluate the enthalpy increment, entropy change, and reduced Gibbs energy change of the bismuth titanates.

The apatite-like Pb9Pr(GeO4)3(VO4)3 and Pb9Sm(GeO4)3(VO4)3 compounds were prepared by solid-phase synthesis using oxides as starting chemicals: PbO, Pr2O3 (Sm2O3), GeO2, and V2O5. The successive annealing was carried out at 773–1073 K in the air. The effect of rare-earth elements on the structure of the Pb9R(GeO4)3(VO4)3 (R = La, Pr, Nd, Sm) apatites and basic thermodynamic functions was investigated. The temperature dependence (350–1050 K) of the heat capacity of the Pr(Sm)-containing apatites has been determined by differential scanning calorimetry. It has been established that the Cp = f(T) curve for the Pb9Pr(GeO4)3(VO4)3 compound has an extremum associated with a polymorphic transformation in the region of 978 K.

The Y0.4Bi0.6VO4 and Y0.6Bi0.4VO4 solid solutions two-phase at xBi = 0.95, 0.90, and 0.80 have been formed by the solid-phase synthesis from the initial Y2O3, Bi2O3, and V2O5 oxides burned in air at a temperature of 1173 K for 200 h and their high-temperature heat capacity has been measured in the range of 350–1000 K by differential scanning calorimetry. The thermodynamic properties of the solution solutions have been calculated using the data obtained.

— Single-phase LuGaTi 2 O 7 samples have been prepared by solid-state reaction in a starting mixture of Lu 2 O 3 , Ga 2 O 3 , and TiO 2 via sequential firing in air at temperatures of 1273 and 1573 K. The crystal structure of the lutetium gallium dititanate has been determined by the Rietveld method (profile analysis of X-ray diffraction patterns of polycrystalline powders): sp. gr. Pcnb ; a = 9.75033(13) Å, b = 13.41425(17) Å, c = 7.29215(9) Å, V = 957.32(2) Å 3 , d = 6.28 g/cm 3 . The heat capacity of LuGaTi 2 O 7 has been determined as a function of temperature by differential scanning calorimetry in the range 320–1000 K. The C p ( T ) data thus obtained have been used to calculate the principal thermodynamic functions of the oxide compound.

The apatite-like Pb9Pr(GeO4)3(VO4)3 and Pb9Sm(GeO4)3(VO4)3 compounds were prepared by solid-phase synthesis using oxides as starting chemicals: PbO, Pr2O3 (Sm2O3), GeO2, and V2O5. The successive annealing was carried out at 773–1073 K in the air. The effect of rare-earth elements on the structure of the Pb9R(GeO4)3(VO4)3 (R = La, Pr, Nd, Sm) apatites and basic thermodynamic functions was investigated. The temperature dependence (350–1050 K) of the heat capacity of the Pr(Sm)-containing apatites has been determined by differential scanning calorimetry. It has been established that the Cp = f(T) curve for the Pb9Pr(GeO4)3(VO4)3 compound has an extremum associated with a polymorphic transformation in the region of 978 K.