Uniaxial Stress Dependence of the Permittivity and the Hardening Effect in the Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 System

The dependence of the permittivity on the uniaxial compressive stress was investigated for the case of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 ceramics. For the morphotropic sample the results showed a strong increase in the stress dependence compared to pure Na0.5Bi0.5TiO3. Nevertheless, a threshold stress was observed, below which the domain switching was hindered. The threshold stress value and, thus, the hardness of the materials increased with increasing K0.5Bi0.5TiO3 content. In the hard tetragonal samples the permittivity increased with the stress loading; however, if the mechanical load exceeded a threshold level, the hardening effect vanished. The results are discussed in terms of the defect dipole model for the stabilization of the domain configuration. The stabilization was the highest in pure K0.5Bi0.5TiO3, for which a poled remanent state was preserved at stresses higher than 200 MPa.