Synthesis, structure and piezo-/ferroelectric properties of a novel bismuth-containing ternary complex perovskite solid solution

To develop high-performance piezo-/ferroelectric materials and to understand their underlying physical and chemical mechanisms, a novel ternary solid solution has been synthesized by a solid state reaction method in the form of ceramics with compositions across the morphotropic phase boundary (MPB). This ternary system is formed by incorporating Bi-based complex perovskite Bi(Zn_2/3Nb_1/3)O₃ (BZN) into the relaxor-based binary solid solution of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT). The MPB structure, relaxor-to-ferroelectric phase transformation, local polar structure, ferroelectric properties and static and bipolar piezoelectric responses were investigated. X-ray diffraction analysis indicates that the (0.95 - x)PMN-0.05BZN-xPT solid solution transforms from a rhombohedral phase to a tetragonal phase when the composition is varied across the MPB which is located at x ∼ 0.30 to 0.33. Enhanced relaxor behaviour is found in this system and the relaxor state transforms into a ferroelectric phase spontaneously upon cooling, or under application of an electric field. The incorporation of BZN into PMN-PT results in the suppression of the MPB-related depoling (at T_RT) and a significant enhancement of piezoelectric and ferroelectric properties compared with those of PMN-PT binary ceramics. The optimum properties are found in the MPB composition with a static piezoelectric coefficient d₃₃ = 805 pC N^-1, an electromechanical coupling factor k_p = 0.57, a remanent polarization P_r = 30 μC cm^-2 and a coercive field of E_C = 7.9 kV cm^-1. This enhancement of properties is attributed to the beneficial effects of BZN which enhances the structural distortion due to the lone-pair electrons on Bi³⁺ and the ferroelectrically active Zn²⁺ and Nb⁵⁺, and to the enhanced relaxor behaviour arising from the increase of the local disorder and the nanodomain effect. With its strengthened properties, the (0.95 - x)PMN-0.05BZN-xPT system becomes a promising electronic ceramic material for such devices as actuators, sensors, capacitors, and transducers for a wide range of applications.