Negative longitudinal electrostriction in polycrystalline ferroelectrics: a nonlinear approach

Abstract

The longitudinal strains ξ3 of initially unpoled polycrystalline (ceramic) ferroelectrics having different composition were measured as a function of the electric field strength E. The electric field dependences of the longitudinal piezoelectric coefficients d33(E) and longitudinal electrostriction coefficients M33(E) were calculated from the virgin ξ3(E) curves and analysed. It was shown that taking into account the polarization nonlinearity (that is, the dependence of dielectric susceptibility on E) leads to nonmonotonic field dependences d33(E) and M33(E). In a nonlinear system, the electrostrictive effect is due not only to polarization but also to the dependence of dielectric susceptibility on the electric field strength. The large magnitude of the dielectric susceptibility of soft and relaxor ferroelectric ceramics is responsible for the giant electrostriction being positive in low electric fields and negative in strong ones. The possibility of giant negative electrostriction existing has been found for the first time. In strong electric fields, the strain gain has a limitation because of the competition between the positive contribution of the piezoelectric effect and the negative contribution of electrostriction to the strain.