Influence of Orthorhombic-Tetragonal Phase Transition on Microwave Dielectric Dispersion of BaTiO₃ Ceramic

The temperature evolution of dielectric dispersion is examined for a coarse-grained BaTiO₃ ceramic in the frequency range from 40 Hz to 1 GHz and over the temperature interval between ?50°C and 80°C, which thus includes the orthorhombic-tetragonal phase transition and covers the large part of common usage temperature region. We find an important physical phenomenon that the phase transition has a notable influence on the microwave dielectric dispersion. The dielectric permittivity ε' shows a maximum, whereas the characteristic frequency f_r displays a minimum in the vicinity of orthorhombic-tetragonal phase transition temperature. Also, a large difference in the f_r values is observed in the tetragonal phase between the heating process and the cooling process. It seems that the experimentally found phenomenon can be explained by the previously suggested mechanism of the emission of elastic shear waves from ferroelastic domain walls.