Low-Temperature Thermodynamic Functions of Gadolinium Hafnate (Gd 2 Hf 2 O 7 )

The isobar heat capacity of Gd2Hf2O7 is studied for the first time by adiabatic calorimetry in the range 80–298.15 K. It is shown that Cp of gadolinium hafnate changes monotonically and no anomalies are observed. The temperature dependences of the principal thermodynamic functions of Gd2Hf2O7 in the range 10–300 K are established. The heat capacity, entropy, reduced Gibbs energy, and enthalpy are determined for standard conditions: $$ {C}_p^{\circ } $$ (298.15 K) = 224.2 ± 0.9 J × × mol–1·K–1, S°(298.15 K) = 237.1 ± 2 J · mol–1 · K–1, Φ′ (298.15 K) = 109.4 ± 1.6 J · mol–1 · K–1, and H°(298.15 K) – H°(0 K) = 38084 ± 190 J · mol–1. The temperature dependence of the Gd2Hf2O7 heat capacity is evaluated using the Neumann–Kopp rule of additivity. The difference between the experimental and evaluated heat capacities of Gd2Hf2O7 in the range 80–298.15 K is no more than 3.4%, while the difference in $$ {C}_p^{\circ } $$ (298.15 K) is 0.4%.