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

Abstract

Due to the similar electronic configurations of Bi³⁺ and Pb²⁺ ions, Bi_0.5Na_0.5TiO₃ (BNT) generally serves as a critical substitution in Pb-based piezoelectric systems. However, the performance of BNT-based series still exhibits a significant gap compared with Pb-based materials, despite their various modifications such as traditional phase boundary engineering and texture engineering. 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. The current methods mainly rely on high-throughput ion doping or multiphase composites. To address these issues, the (1 − x)Bi_0.5Na_0.5TiO₃–xBi_0.2Na_0.2Ba_0.2Sr_0.2Ca_0.2TiO₃ series are prepared through a solid-state reaction based on the strong disorder brought by a high-entropy strategy. In this work, the disorder state is quantitatively introduced by adjusting a 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 k_p reach 128 pC N⁻¹ and 0.43, which are 1.58 and 1.65 times that of the parent BNT, respectively. The highest d₃₃ of 151 pC N⁻¹ is obtained with an increase in the temperature. The domain evolution indicates that this high-entropy strategy can bring about a novel stripe-like structure, which can maintain long-range order and polar characteristics within the 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 foundation for the development of lead-free piezoelectric devices such as BNT-based sensors and transducers.