Nanostructured lead-free ferroelectric Na0.5Bi0.5TiO3–BaTiO3 whiskers: synthesis mechanism and structure

Abstract

Nanostructured lead-free ferroelectric Na_0.5Bi_0.5TiO₃–BaTiO₃ (NBTBT) whiskers with a high aspect ratio were synthesized topochemically using Na₂Ti₆O₁₃ (NTO) as a host structure for the first time. High energy X-ray diffraction coupled with an atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of the lead-free NBTBT whiskers, which was found to be rhombohedral, i.e. a ferroelectric enabling type. High resolution transmission electron microscopic (HRTEM) analysis revealed local monoclinic-type structural distortions, indicating a modulated structure at the nanoscale in the morphotropic phase boundary (MPB) composition of the lead-free NBTBT whiskers. The structural rearrangement during the synthesis of the lead-free NBTBT whiskers was found to occur via translation of the edge shared octahedra of NTO into a corner sharing coordination. High temperature morphological changes that depict the disintegration of the isolated whiskers into their individual grains due to the higher grain boundary energy have been found to occur in close analogy with Rayleigh-type instability.