Advances in mitigating the Td-d33 trade-off via compositionally graded diffusion in BNT-based piezoceramic

A notoriously unresolved conflict that the substantial increment of depolarization temperature Td was generally accompanied by the sharply deterioration of piezoelectric constant d33 in Bi0.5Na0.5TiO3-based (BNT-based) piezoceramics severely limit their practical applications. Herein, a new strategy by Ba2+ gradient diffusion layer in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (BNT-6BT) ceramic via interface-diffused sintering to suppress the ferroelectric-relaxor phase transition is presented to manipulate the incompatibility of Td and d33. By this strategy, the compositionally graded diffusion in the BNT-6BT ceramic can offer both the properties simultaneously with the Td deferring from 109 °C to 170 °C and maintaining the initial d33 (145pC/N). Furthermore, by integrating the interface-diffused sintering and quenching process, the TF-R is significantly deferring from 115 °C to 214 °C while the d33 * is retaining the initial value (d33 *=Smax/Emax=258 pm/V). Diffusion phase transition caused by Ba2+ concentration gradient promotes the greatly increased tetragonal phase ratio and the development of built-in field thereby leading to well-balanced performance between Td and d33 in BNT-6BT ceramic. Our work opens a new avenue for developing the high-performance lead-free BNT-based piezoceramics.