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

Abstract

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.