Electric field and mechanical stress driven structural inhomogeneity and compositionally induced relaxor phase transformation in modified BaTiO3based lead-free ferroelectrics

Abstract

The compositionally induced ferroelectric to relaxor transformation via diffuse phase transition and structural disorder by external stimuli is explored in lead-free Ba_1-x(Bi_0.5Li_0.5)_xTiO₃(x= 0, 0.05, 0.1, 0.15, and 0.20) ferroelectric system. X-ray diffraction studies reveal the coexistence of the monoclinic phase along with the orthorhombic and tetragonal phases in BaTiO_3,which could be the reason for its superior dielectric properties. The dielectric studies reveal that thex= 0.15 sample shows intrinsic dielectric relaxation due to the quenched-in random field caused by the atomic displacement. The ferroelectric to relaxor phase transformation is analysed by modified Curie-Weiss law. Furthermore, the driving forces for the relaxor behaviour in the system are attributed to the compositionally induced charge disorder, quenched-in random field, and oxygen vacancy related defects in the BBLT system. The detailed structural analysis on the relaxor ferroelectric samples displays direct evidence for the electric field and mechanical stress driven structural inhomogeneity. Notably, mechanically stressed and electrically poledx= 0.15 sample exhibits a remarkable 50% and 37% increase in orthorhombic phase fraction, respectively. Overall, the comprehensive studies on the lead-free modified BaTiO₃samples give further insight into understanding the relaxor system.

Keywords: diffuse phase transition; ferroelectrics; relaxor; structural transition; x-ray diffraction.