Thermochemistry of new holmium-calcium tellurite

Abstract

The new double holmium-calcium tellurite was synthesized by the ceramic technology. The formation of the equilibrium composition of the compound was monitored by X-ray diffraction. Double tellurite of holmium HoCaTeO4.5 has been synthesized according to the results of X-ray analysis. Calorimetric investigation of the heat capacity of the new double tellurite HoCaTeO4.5 was carried out for the first time in the range of 298.15– 673 K. Calibration of the device was carried out on the basis of determining the thermal conductivity of a heat meter. The calorimeter performance was checked by measuring the heat capacity of α-Al2O3. The experimental data and the specific molar heat capacities have been processed by methods of mathematical statistics. The dependence equation Cp 0~f (T) has been derived on the basis of experimental data. According Cp 0~f (T) and the calculated value of S0(298.15) of tellurite the temperature dependence of the thermodynamic functions H0(T)–H0(298.15), S0(T) and Фхх(Т) have been determined. Abnormal jumps have been observed on the dependence Cp 0~f (T) associated probably with the phase transitions of the second order. The thermodynamic characteristics of the new tellurite can serve as source materials for inclusion in fundamental data banks and reference books, used to predict the thermochemical constants of similar compounds.