Heat Capacity of Yb₄Hf₃O₁₂ at 57–302 K.

Abstract

The heat capacity of Yb₄Hf₃O₁₂ is studied for the first time in the range 57–302 K by adiabatic calorimetry. It is shown that С_р of ytterbium hafnate changes monotonically and no anomalies are observed. Temperature dependencies of the principal thermodynamic functions in the range 10–300 K are obtained. The heat capacity, entropy, reduced Gibbs energy, and enthalpy are determined for standard conditions: C°_p(298,15K) = 408,4  ± 1,6 J • mol^–1 • К^–1; S^°(298,15K)  = 410,5  ± 3,3 J • mol^–1 • К^–1;  Ф’ (298,15K) = 187,2 ± 2,8 J • mol^–1 • К^–1; H°(298,15K) - H° (0K) = 66566 ± 333 J • mol^–1. The difference between the experimental heat capacities and those evaluated by the Neumann–Kopp rule of additivity (as a weighed sum of heat capacities of oxides) in the range 70–300 K is no more than 4.65%, while the difference in C°p(298,15K)is 0.7%.