Synthesis and High-Temperature Heat Capacity of Pb8La2(GeO4)4(VO4)2 and Pb8Nd2(GeO4)4(VO4)2 with the Apatite Structure

Abstract

The Pb₈La₂(GeO₄)₄(VO₄)₂ and Pb₈Nd₂(GeO₄)₄(VO₄)₂ germanatovanadates with the apatite structure have been prepared by solid-state reactions, by sequentially firing stoichiometric mixtures of PbO, La₂O₃ (Nd₂O₃), GeO₂, and V₂O₅ in air at temperatures of 773, 873, 973, and 1073 K. The effect of temperature on the heat capacity of the resultant polycrystalline samples has been studied by differential scanning calorimetry at temperatures from 350 to 950 K using polycrystalline samples. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of the lead lanthanum and lead neodymium germanatovanadates.