Calorimetric Study of the La2Hf2O7 Heat Capacity in the Range 57-302 K

The heat capacity of La2Hf2O7 has been studied in the range 57-302 K by adiabatic calorimetry. The heat capacity C (p) of lanthanum hafnate changes monotonically and there are no anomalies. The values of heat capacity, entropy, enthalpy, and reduced Gibbs energy have been determined in standard conditions: C (p) (A degrees) (298.15 K) = 229.39 A +/- 0.92 J center dot mol(-1) center dot K-1, SA degrees (298.15 K) = 246.9 +/- 2 J x x mol(-1) a (TM) K-1, Dcurrency signA degrees (298.15 K) = 114.76 +/- 1.72 J a (TM) mol(-1) a (TM) K-1, and HA degrees (298.15 K)-HA degrees (0 K) = 39403 +/- 197 J a (TM) mol(-1). In the series of isostructural La2Zr2O7 -> La2Hf2O7 compounds, atomic oscillation frequency in the lattice decreases and low-temperature heat capacity increases with greater mass of oscillator atoms from Zr to Hf.