Synthesis and Thermodynamic Properties of the Ca₃Sc₂Ge₃O₁₂ Germanate

The calcium strontium germanate Ca₃Sc₂Ge₃O₁₂ has been prepared by solid-state reaction, by firing a stoichiometric mixture of CaO, Sc₂O₃, and GeO₂ in air at temperatures from 1273 to 1623 K. Using X-ray diffraction data for single-phase samples, we have determined the unit-cell parameter of Ca₃Sc₂Ge₃O₁₂ crystals (garnet structure, sp. gr. Ia \(\bar {3}\) d, a = 12.508(48) Å, V = 1956.92(2) ų). The heat capacity of polycrystalline samples has been determined in the range 320–1050 K using differential scanning calorimetry. The results have been used to calculate thermodynamic functions of the calcium strontium germanate.