V. V. Beletskii

High-temperature heat capacity and thermodynamic properties of Tb2Sn2O7

Tb2Sn2O7 has been prepared by solid-state reaction in air at 1473 K over a period of 200 h and its isobaric heat capacity has been studied experimentally in the range 350–1073 K. The Cp(T) data for this compound have no extrema and are well represented by the classic Maier–Kelley equation. The experimental Cp(T) data have been used to evaluate the thermodynamic properties of terbium stannate (pyrochlore structure): enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(Т).

Synthesis and heat capacity of PrVO4 in the temperature interval of 396–1023 K

The heat capacity of orthovanadate PrVO4 prepared via solid-phase synthesis was measured by differential scanning calorimetry in the temperature interval of 396–1023 K. The experimental heat capacities were used to calculate the thermodynamic functions of PrVO4 (enthalpy change H0(T) − H0(396 K) and entropy change S0(T) − S0(396 K)).

High-temperature heat capacity of stannates Er2Sn2O7 and Tm2Sn2O7

Erbium stannate Er2Sn2O7 and thulium stannate Tm2Sn2O7 with a pyrochlore-type structure were produced by solid-phase synthesis by calcining stoichiometric mixtures of the respective oxides in air at 1473 K for 240 and 200 h. The high-temperature heat capacity of Er2Sn2O7 and Tm2Sn2O7 was studied by differential thermal calorimetry at 353–1000 K. From the experimental dependences CP = f(T), the thermodynamic functions (enthalpy change, entropy change, and reduced Gibbs free energy) of oxide compounds were calculated.

Synthesis and investigation of the heat capacity of Sm2Sn2O7 in the 346–1050 K range

Optimal conditions for the synthesis of Sm2Sn2O7 with pyrochlore crystal structure by solid-phase reactions were determined. The effect of temperature (346–1050 K) on the molar heat capacity of samarium stannate was studied by differential scanning calorimetry. Thermodynamic properties of Sm2Sn2O7 in the temperature range under study were determined using the experimental data.

High-temperature heat capacity and vibrational spectra of Eu2Sn2O7

The Eu2Sn2O7 compound has been prepared by solid-state reaction (by sequentially firing a stoichiometric mixture of Eu2O3 and SnO2 in air at 1273 and 1473 K) and its heat capacity has been determined by differential scanning calorimetry in the temperature range 370–1000 K. The heat capacity data have been used to evaluate the thermodynamic properties of europium stannate: enthalpy increment H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and reduced Gibbs energy Ф°(T). Raman spectra of Eu2Sn2O7 polycrystals with the pyrochlore structure have been measured in the range 200–1200 cm–1.

Synthesis and high-temperature heat capacity of Gd2Sn2O7

Gd2Sn2O7 gadolinium stannate with the pyrochlore structure has been prepared by solid-state reaction and its high-temperature heat capacity has been determined by differential scanning calorimetry in the temperature range 350–1020 K. The Cp(T) data are shown to be well represented by the classic Maier–Kelley equation. The experimental Cp(T) data have been used to evaluate the thermodynamic functions of gadolinium stannate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т).

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb2V2O7 and orthovanadate Pb3(VO4)2

The heat capacities of Pb2V2O7 and Pb3(VO4)2 as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The CP = f(T) curve for Pb2V2O7 is described by the equation Cp = (230.76 ± 0.51) + (73.60 ± 0.50)×10-3T − (18.38 ± 0.54)×105T-2 in the entire temperature range. For Pb3(VO4)2, there is a well-pronounced extreme point in the CP = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.

High-temperature heat capacity of stannates Pr2Sn2O7 and Nd2Sn2O7

Oxide compounds Pr2Sn2O7 and Nd2Sn2O7 have been obtained by solid-phase synthesis. The effect of temperature on the heat capacity of Pr2Sn2O7 (360–1045 K) and Nd2Sn2O7 (360–1030 K) has been studied using differential scanning calorimetry. The thermodynamic properties of the compounds (changes in enthalpy, entropy, and the reduced Gibbs energy) have been calculated by the experimental data of Cp = f(T).

High-temperature heat capacity and thermodynamic properties of Pb4V2O9 and Pb8V2O13

The molar heat capacity of Pb4V2O9 and Pb8V2O13 in the temperature range 350–1000 K was measured by differential scanning calorimetry. It was determined that the plot Cp = f(T) for Pb8V2O13 has an extremum within the range 416–516 K, which is due to a phase transition. A correlation was found between the heat capacity and composition of oxides in the PbO–V2O5 system. The data obtained allowed one to predict the specific heat capacity value for Pb(VO3)2.

Synthesis and High-Temperature Heat Capacity of Y 2 Ge 2 O 7

Yttrium germanate Y2Ge2O7 was prepared by solid-phase synthesis from a stoichiometric Y2O3–GeO2 mixture under multistage calcination in air within a temperature range of 1273–1473 K. The molar heat capacity of polycrystalline samples was measured by differential scanning calorimetry (DSC), and the CP = f(T) dependence was used to calculate the thermodynamic properties of yttrium digermanates, such as the enthalpy and entropy changes and the reduced Gibbs energy.