Achieving synergistic electromechanical and electrocaloric responses by local structural evolution in lead-free BNT-based relaxor ferroelectrics

Abstract

• Inducing relaxor evolution by adjusting intrinsic A-site Na + /K + ratio. • Achieving large combined electromechanical and electrocaloric responses. • Realizing a larger electrocaloric endothermic peak at a low electric field. • Obtaining high electrocaloric strength and large electrostrictive coefficient. • Broadening the operating-temperature span. Self-actuating cooling materials based on synergistic electromechanical (EM) and electrocaloric (EC) responses are expected to lead next-generation of intelligent cooling devices. However, most current materials with the two responses present poor performance, narrow operation-temperature span and high driving electric field, and even contain toxic lead. Here, environmentally benign lead-free Bi 0.5 Na 0.5 TiO 3 -based (BNT) system was designed to achieve large combined response of two effects in a large temperature span by adjusting intrinsic A-site Na + /K + ratio to induce relaxor evolution. Simultaneously, high EC strength and large electrostrictive coefficient over a wide temperature range were obtained to resolve these challenges. The local-structural evolution is studied in detail to provide a theoretical basis for future application of this intelligent material. A novel asymmetric EC response presenting a larger endothermic peak was realized at a low electric field (<3 kV mm −1 ), which can provide a guideline for the development of low-driving-field EC materials to a certain extent. The phase-field simulation was performed to predict this unique behavior by describing the corresponding dipole coupling states under various electric fields.