High-Temperature Heat Capacity of Pb10 – xNdx(GeO4)2 + x(VO4)4 – x (x = 0–3) Apatites

We obtained Pb10 – xNdx(GeO4)2 + x(VO4)4 – x (x = 0–3) compounds with an apatite structure by solid-phase synthesis from initial oxides PbO, Nd2O3, GeO2, and V2O5 with successive annealing at 773–1073 K in the air. Their high-temperature heat capacity was measured by differential scanning calorimetry. The thermodynamic functions (changes in enthalpy, entropy, and reduced Gibbs energy) are calculated using the experimental dependences of Cp = f(T).