Heat Capacity of Yb sub(4)Hf sub(3)O sub(12) at 57-302 K

The heat capacity of Yb sub(4)Hf sub(3)O sub(12) is studied for the first time in the range 57-302 K by adiabatic calorimetry. It is shown that C sub(p) of ytterbium hafnate changes monotonically and no anomalies are observed. Temperature dependences 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 sub( )p super( degree ) (298.15 K) =408.4 plus or minus 1.6 J . mol super(-1) . K super(-1), S degree (298.15 K) = 410.5 plus or minus 3.3 J . mol super(-1) . K super(-1), Phi '(298.15 K) = 187.2 plus or minus 2.8 J . mol super(-1) . K super(-1), and H degree (298.15 K) - H degree (0 K) = = 66566 plus or minus 333 J . mol super(-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 sub( )p super( degree ) (298.15 K) is 0.7%.