Heat capacity and thermal expansion studies of relaxors

Heat capacity and thermal expansion of three perovskite-like solid solutions with nonisovalent PbMg1/3Nb2/3O3, PbFe1/2Ta1/2O3 and isovalent Ba0.92Ca0.08U0.76Zr0.24O3 substitution were measured using the methods of calorimetry and optical-mechanical dilatometry in a wide temperature range. The blurred anomalies in the C-p(T) and alpha(T) dependences are observed at Burns temperature, at the temperature of the dielectric permittivity maximum and at the temperature of the phase transition into ferroelectric state. The results are discussed together with the data on the structure and dielectric properties in the framework of spherical random bond-random field model.