Electric field forced c-axis oriented growth of polar nanoregions and rapid switching of tetragonal domains in BNT-PT-PMN ternary system

A normal to relaxor ferroelectric phase transition was observed to accompany a tetragonal to pseudocubic phase transformation in (1 − x)(0.84(Bi0.5Na0.5)TiO3-0.16PbTiO3)-xPb(Mg1/3Nb2/3)O3 (BNT-PT-xPMN) ceramics. The addition of PMN was found to gradually refine the domain morphology, such that the morphotropic phase boundary intrinsically evolved into coexisting tetragonal ferroelectric microdomains and pseudocubic nonergodic polar nanoregions (PNRs). The mechanism of generating remarkably enhanced electrostrains was ascribed to the oriented growth of PNRs and subsequently rapid switching of tetragonal domains along the electric field direction by means of in situ synchrotron X-ray diffraction, through which the symmetry of PNRs was found to be intrinsically tetragonal. The key reason for an additional polarization current peak was attributed to a significant reduction of the unit cell anisotropy at a critical field at which a simultaneous shrinkage of the lattice constant ct led to a relatively low electrostrain compared to those previously reported in other bismuth-containing relaxor ferroelectrics.