Electric field and temperature dependence of the local structural disorder in the lead-free ferroelectric Na_0.5Bi_0.5TiO₃: An EXAFS study

Abstract

The complex nature of the structural disorder in the lead-free ferroelectric Na_1/2Bi_1/2TiO₃ has a profound impact on the perceived global structure and polar properties. In this paper, we have investigated the effect of electric field and temperature on the local structure around the Bi and Ti atoms using extended x-ray absorption fine structure. Detailed analysis revealed that poling brings about a noticeable change in the bond distances associated with the Bi-coordination sphere, whereas the Ti coordination remains unaffected. We also observed discontinuity in the Bi-O bond lengths across the depolarization temperature of the poled specimen. These results establish that the disappearance of the monoclinic-like (Cc) global distortion, along with the drastic suppression of the short-ranged in-phase octahedral tilt after poling [B. N. Rao et al., Phys. Rev. B 88, 224103 (2013)] is a result of the readjustment of the A-O bonds by the electric field, so as to be in conformity with the rhombohedral R3c structure.