Deciphering the relationships among phase boundary, domain structure, and excellent electrical properties of ternary Bi0.5Na0.5TiO3-Bi0.2Sr0.7TiO3-NaNbO3 ferroelectrics

Abstract

Bi0.5Na0.5TiO3-based ferroelectric ceramics have broad application prospects due to their excellent electrical properties and are considered to be one of the most promising functional materials to supersede lead-based materials. Here, 0.9Bi0.5Na0.5TiO3-0.1Bi0.2Sr0.7TiO3-xNaNbO3 (BNT-BST-xNN) ternary lead-free ferroelectric ceramics were prepared, and the origin of their excellent dielectric properties was investigated in terms of phase boundary and domain structure. The introduction of NN led to a phase transition from the ferroelectric rhombohedral phase (R3c) to the relaxor tetragonal phase (P4bm), and the two phases coexisted in the BNT-BST-xNN ternary solid solution with x ranging from 0.06 to 0.2. Meanwhile, the macroscopic domain of BNT-BST was destroyed and replaced by highly active polar nano-regions (PNRs) of the P4bm phase, leading to an increase in local structural disorder and enhanced relaxor behavior. A dielectric constant (εr) of ∼1765 (150 °C) with Δε/ε150 °C less than 15% over a broad range from 80 to 328 °C was achieved in the BNT-BST-0.15NN, and an excellent energy storage property (Wrec = 3.3 J/cm3) was obtained under a low electric field (190 kV/cm). More specifically, the relationship among phase boundary, domain structure, and excellent electrical properties was achieved based on Rietveld refinements and the dielectric/ferroelectric characterizations. This work provides a deep insight into the phase evolution and its impact on the electrical properties of the BNT-based relaxor ferroelectrics.