Electric-field-induced phase transition in the relaxor ceramics based on PMN–PT

The mechanisms of formation of a plateau in dependences of the reversible permittivity on the external electric field strength in a ceramic sample of the $y$PZN–$m$PMN–$n$PNN–$x$PT ($x$ = 0, 3; $y$ = 0.0982; $m$ = 0.4541; $n$ = 0.1477) system have been analyzed using X-ray diffraction and atomic force microscopy. It has been shown that, in electric fields corresponding to the permittivity anomaly, there occurs an induced phase transition from the heterophase (tetragonal + pseudocubic) state to the single-phase (tetragonal) state. This leads to significant strains of the tetragonal unit cell (up to 0.1%) and the termination of 90$^\circ$ domain switching. The proposed qualitative model of the formation of the observed dielectric anomaly is based on two processes occurring with an increase in the electric field strength: the growth of polar regions of the tetragonal phase and their switching.