High temperature heat capacity and thermodynamic properties of CaEu$_2$Ge$_4$O$_{12}$ and CaHo$_2$Ge$_4$O$_{12}$ germanates in the range of 320–1050 K

The germanates CaEu$_2$Ge$_4$O$_{12}$ and CaHo$_2$Ge$_4$O$_{12}$ were synthesized from stoichiometric mixtures of CaO, Eu$_2$O$_3$ (Ho$_2$O$_3$) and GeO$_2$ by sequential firing in air in the temperature range 1223–1373 K. Their crystal structure has been refined using X-ray diffraction. The heat capacity $C_p$ of the obtained germanates was measured by differential scanning calorimetry in the region of 320–1050 K. Based on the experimental dependence of $C_p(T)$ , the thermodynamic characteristics of the analyzed oxide compounds are calculated.