Calorimetric research of a heat capacity of a triple lanthanum tellurite in the range of 298.15–673 К

Abstract

This paper presents detailed results of new lanthanum tellurite synthesis and its heat capacity calorimetric research. For the first time, a triple lanthanum tellurite was synthesized by the solid-phase method from oxides of lanthanum, nickel (II), tellurium (IV) and calcium carbonate. The generation of the equilibrium composition of the synthesized compound was controlled by the method of X-ray diffraction analysis (XDA) on the diffractometer DRON-2.0. By the results of the XDA it was established that there was synthesized a triple lanthanum tellurite La2CaNiTeO7. Heat capacity at constant pressure of the synthesized tellurite was researched by the method of dynamic calorimetry at the range of 298.15–673 К. Based on the experimental data, the equations, describing dependencies of heat capacity of the compound on temperature were calculated. When studying the temperature dependences of the heat capacity of La2CaNiTeO7, abnormally sharp λ-like peaks probably associated with second-order phase transitions, were observed at 423 K. Temperature dependencies of thermodynamic functions of La2CaNiTeO7 Sº(T), Hº(T)–Hº(298,15), Фхх(Т) were calculated based on the experimental data Срº(Т) and the calculated value Sº (298.15).