Extrinsic response anisotropy in ferroelectric perovskite polycrystals

A study on the anisotropy of the nonlinear dielectric response in donor- and acceptor-doped Pb(Zr0.6Ti0.4)O3 ceramics is presented. They have been tested in two directions, parallel to and normal to the poling direction. The results reveal a noticeable anisotropic behavior related to a different movement of domain walls when the field is applied in either direction. A simple model for the domain wall movement, which can be applied to any perovskite ceramic, is developed in order to explain this behavior. It is supposed that the grains are monocrystals with a lamellar structure of non- 180∘ domains. It is proved that in such a structure, the extrinsic contribution is greater in the direction normal to the poling direction than in that parallel to this direction. Moreover, acceptor-doped ceramics show a higher anisotropy than donor-doped ceramics. This fact can be explained by taking into account that the complex defects show a preferential orientation, so they produce a stronger domain wall pinning in the poling direction than in the normal one.