Local disorder in Na0.5Bi0.5TiO3-piezoceramic determined by 3D electron diffuse scattering

Alexandra Neagu,Cheuk-Wai Tai

doi:10.1038/s41598-017-12801-w

Abstract

Local structural distortions in Na0.5Bi0.5TiO3-based solid solutions have been proved to play a crucial role in understanding and tuning their enhanced piezoelectric properties near the morphotropic phase boundary. In this work all local structural disorders in a lead-free ternary system, namely 85%Na0.5Bi0.5TiO3-10%Bi0.5K0.5TiO3-5%BaTiO3, were mapped in reciprocal space by 3D electron diffraction. Furthermore, a comprehensive model of the local disorder was developed by analysing the intensity and morphology of the observed weak diffuse scattering. We found that the studied ceramics consists of plate-like in-phase oxygen octahedral nanoscale domains randomly distributed in an antiphase tilted matrix. In addition, A-site chemical short-range order of Na/Bi and polar displacements contribute to different kinds of diffuse scattering. The proposed model explains all the observed diffraction features and offers insight into the ongoing controversy over the nature of local structural distortions in Na0.5Bi0.5TiO3-based solid solutions.

Highlights

Recent environmental regulations have questioned the use of lead-based piezoceramics in electronic applications owing to the high toxicity of lead and its derivatives, lead oxide[1,2]
Features: (i) broad diffuse regions around all Bragg peaks that have been modelled using a pseudorandom occupation of the A-site by Na/Bi together with an atomic size effect[26] and (ii) “L-shaped” diffuse streaks that emanate from the Bragg peaks and extend towards lower q-values which have been explained by assuming the presence of nanometer-scale platelet structures of highly correlated Na/Bi atomic positions, analogous to Guinier Preston zones (GPZs)[26]
Earlier studies of both pure NBT26,28,33,35 and NBT-BT29–31 have revealed a highly disordered structure for these materials, so 85NBT-10BKT-5BT ternary solid solution represents a good candidate for the study of short-range order/disorder by 3D electron diffraction

Summary

Introduction

Recent environmental regulations have questioned the use of lead-based piezoceramics in electronic applications owing to the high toxicity of lead and its derivatives, lead oxide[1,2]. More recent high-resolution X-ray studies[16,17] propose, on the other hand, a monoclinic Cc symmetry with a−a−c− octahedral tilting Another proposed structure suggests that the equilibrium state of NBT at room temperature consists of a coexistence of R3c and Cc phases[18]. From TEM studies two models have been proposed in order to explain the observed superstructure reflections and diffuse scattering intensity. The fact that the RED method provides a 3D reciprocal-space volume makes the analysis of diffuse scattering intensity more straight forward than in the case of 2D electron diffraction patterns. We propose a structural model to explain all the observed electron diffuse scattering intensity and superstructure reflections To our knowledge this is the first time 3D electron diffuse scattering result together with a comprehensive structural model for understanding the local disorder in a NBT-ternary compound are reported

Methods

Results

Conclusion