The Structural Complexity of (Bi0.5Na0.5)TiO3-BaTiO3 as Revealed by Raman Spectroscopy

TL;DR

This study uses Raman spectroscopy to investigate the structural phases of (Bi0.5Na0.5)TiO3-BaTiO3, revealing a temperature-independent morphotropic phase boundary and short-range ionic displacements above 370 K, which impact piezoelectric properties.

Contribution

It provides new insights into the phase diagram and structural behavior of Pb-free ferroelectric (Na1/2Bi1/2)1-xBaxTiO3, especially regarding the morphotropic boundary and high-temperature phases.

Findings

Identification of a temperature-independent morphotropic phase boundary at x ≈ 0.055

No structural phase transition across 370 K for x > 0.055

Presence of short-range ionic displacements above 370 K

Abstract

The structural phase diagram of the Pb-free ferroelectric (Na1/2Bi1/2)1-xBaxTiO3 (NBT-BT), x<0.1, has been explored by Raman spectroscopy at temperatures from 10 to 470 K. The data provide clear evidence for a proposed temperature-independent morphotropic phase boundary at x \approx 0.055. However, there is no evidence for a structural phase transition across T \approx 370 K for x > 0.055, where bulk-property anomalies appear to signal a transition to a nonpolar or antiferroelectric phase. The results identify that the phase above 370 K shows short-range ionic displacements that are identical to those in the long-range-ordered phase below 370 K. These conclusions provide a natural interpretation of the weak piezoelectric response in this system and have important implications for the search for Pb-free piezoelectrics.