Spontaneous ferroelectric order in lead-free relaxor Na1/2Bi1/2TiO3 -based composites

Abstract

Short-range ordered polar nanoregions are key to the giant electromechanical properties exhibited by relaxor ferroelectrics. Stabilization of the long-range ferroelectric order in relaxor systems has typically been achieved by applying external fields. In this work, spontaneous (zero-field) ferroelectric order is demonstrated in the composites constituting of nonergodic relaxor matrix phase $0.91\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2}\mathrm{Ti}{\mathrm{O}}_{3}\text{\ensuremath{-}}0.09\mathrm{BaTi}{\mathrm{O}}_{3}$ with ZnO inclusions. Direct structural evidence is provided for the long-range ferroelectric order in the composites using in situ electric-field-dependent synchrotron investigations and $^{23}\mathrm{Na}$ nuclear magnetic resonance spectroscopy. Thermodynamic analysis incorporating microelasticity reveals the role of spatial residual stress in stabilizing the ferroelectric order. The work provides a direct correlation between the stabilized ferroelectric order and enhanced thermal stability, which can be utilized to guide the design of spontaneous long-range order in other relaxor systems.