Synthesis, structure, and thermophysical properties of Pb$_{10-x}$Bi$_{x}$(GeO$_{4}$)$_{2+x}$(VO$_{4}$)$_{4-x}$ ($x$ = 0 – 3) in the temperature range of 350–950 K

The Pb$_{10-x}$Bi$_{x}$(GeO$_{4}$)$_{2+x}$(VO$_{4}$)$_{4-x}$ ($x$ = 0–3) compounds with an apatite structure have been obtained for the first time from the initial PbO, Bi$_{2}$O$_{3}$, GeO$_{2}$ and V$_{2}$O$_{5}$ oxides by the solid-state synthesis in the temperature range of 773–1073 K. The structure of the compounds has been determined by X-ray diffraction analysis. The effect of temperature on specific heat of the synthesized compounds has been investigated by differential scanning calorimetry. The thermodynamic properties of the compounds have been calculated from the experimental $C_p=f(T)$ data.