Unraveling phase evolution and polarization anomaly driven by chemical strain in BNT-based energy storage ceramics

Chemical substitution in ferroelectric ceramics is widely used to tune phase stability and electromechanical response; however, the role of substitution-induced chemical strain on polarization and structural stability remains insufficiently understood. Herein, we report an anomalous evolution of phase transition temperature and polarization behavior in Ca-doped Bi_0.5Na_0.5TiO₃-based (BNT-based) ferroelectric ceramics, and that being distinct from previously reported chemical modification behavior. Those experimental results are closely related to chemical strain-induced oxygen octahedra rotation arising from isovalent substitution with different ion radii at the A-site, and a qualitative composition-strain-polarization response correlation is established. The chemical strain imposes an internal stress for BNT-based ferroelectric ceramics to increase the polarization switching barrier. Notably, a post-annealing treatment effectively relieves this chemical strain, as evidenced by reduced phase transition temperature, dielectric constant, and slimmed polarization curve, and thus energy efficiency for dielectric energy storage is effectively enhanced. This work not only uncovers the critical role of chemical strain in influencing ferroelectric phase evolution and anomalous polarization changes but also provides a strain engineering way for designing high-performance dielectric energy storage materials.