Heat Capacity of the R2Ge2O7 (R = Pr-Lu, Y) Rare-Earth Germanates

The R2Ge2O7 (R = Pr-Lu, Y) rare-earth germanates have been prepared by solid-state reactions by firing stoichiometric R2O3 + GeO2 mixtures in air at temperatures in the range 1273-1473 K. The unit-cell parameters (a, c, and V) of the R2Ge2O7 (R = Tb-Lu) compounds have been shown to be linear functions of the ionic radius of the rare-earth elements. The high-temperature heat capacity of polycrystalline samples of the germanates has been determined by differential scanning calorimetry in the temperature range 350-1000 K. The variation in the specific heat of R2Ge2O7 has been shown to be correlated with the dependence of the heat capacity of rare-earth oxides on the ionic radius of the rare-earth element within each tetrad.