Lorentz-type relationship of the temperature dependent dielectric permittivity in ferroelectrics with diffuse phase transition

The temperature dependence of the dielectric permittivity of perovskite Ba (Zr_xTi_1-x)O₃ solid solutions, PbMg _1/3Nb_2/3O₃ relaxor, and BaTiO₃ ferroelectric ceramics was measured. It is found that a Lorentz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorentz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorentz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorentz-type law.