Heat Capacity of Pb10 –xLax(GeO4)2 +x(VO4)4 –x (x = 0, 1, 2, 3) Apatites in the Range 320–1000 K

Abstract

Pb_{10 –x}La_x(GeO₄)_{2 +x}(VO₄)_{4 –x} (x = 0, 1, 3) compounds with the apatite structure have been prepared by solid-state reactions via multistep firing of appropriate oxide mixtures in air in the temperature range 773–1073 K. The heat capacity of the synthesized polycrystalline samples has been determined by differential scanning calorimetry. The experimental C_p(T) data have been used to evaluate the thermodynamic properties of the lead lanthanum germanatovanadates: enthalpy increment, entropy change, and reduced Gibbs energy.