Eco-friendly cooling materials with synergistic behavior of electromechanical and electrocaloric effects based on constructing B-site defect field

Nowadays, the materials with synergistic electromechanical (EM) and electrocaloric (EC) effects have gained significant inspiration and expectation for potential self-actuating cooling technology. Such a technique relies on high-performance materials that have both of two effects. Due to environmental consideration, lead-free Bi0.5Na0.5TiO3 (BNT) system was selected to construct the B-site local random field, which successfully achieved high mechanical and electrical performance in a large temperature span, to cope with the challenges of narrow operating temperature region, high driving electric field and poor performance. The relaxor evolution is induced by the difference in valence state, electronegativity and ion radius between substituted and original B-site ions. Going further, it is found that the B-site defects and oxygen vacancies produced by the process are crucial to the reversible polarization response. Phenomenological theory reveals that the essence of reducing the driving electric field in the optimized system lies in lowering the potential barrier from relaxor to ferroelectric phase transition. To a certain extent, our work should therefore motivate the exploration and development of environmental-friendly smart cooling materials.