Investigation into the design and performance regulation of (1-x)Bi0.5Na0.5TiO3-xBi0.2Na0.2Ba0.2Sr0.2Ca0.2TiO3 piezoelectric systems via high-entropy strategy

Abstract

Due to the similar electronic configuration of Bi3+ to Pb2+ ions, Bi0.5Na0.5TiO3 (BNT) generally serves as the critical substitution for Pb-based piezoelectric systems. However, the performance of BNT-based series still exhibits a significant gap compared to Pb-based materials, despite of various modifications such as traditional phase boundary engineering, texture engineering, and so on. Therefore, it is necessary to explore additional regulation strategies based on innovative concepts. Recent research results have shown that the piezoelectricity of BNT can be effectively enhanced by forming relaxor boundaries. Whereas, the current methods mainly rely on high-throughput ion doping or multiphase composites. To address these issues, (1-x)Bi0.5Na0.5TiO3-xBi0.2Na0.2Ba0.2Sr0.2Ca0.2TiO3 series have been prepared through solid-state reaction, based on the strong disorder brought by high-entropy strategy. In this work, the disorder state is quantitatively introduced by adjusting the high-entropy content, thereby distinctly modifying the crystal lattices, domain structure and piezoelectric properties. In the sample with x = 0.25, the values of room-temperature d33 and kp respectively reach 128 pC/N and 0.43, which are 1.58 and 1.65 times that of BNT parent. The highest d33 of 151 pC/N is obtained with increasing temperature. The domain evolution indicates that high-entropy strategy can bring about a novel stripe-like structure, which can maintain long-range order and polar characteristics within nanoscale in different dimensions, thereby obviously enhancing the piezoelectric behavior. This work offers an additional strategy for the performance regulation of lead-free piezoelectrics, broadening the research perspective on the design of piezoelectric ceramics and laying a development foundation for lead-free piezoelectric devices such as BNT-based sensors and transducers.