New strategy for simultaneously achieving enhanced piezoelectricity and deferred Td in Bi0.5Na0.5TiO3-based relaxor ferroelectrics

The inverse relationship between the piezoelectricity and depolarization temperature Td impedes the development of Bi0.5Na0.5TiO3 (BNT)-based ceramics. To realize the goal of enhancing the piezoelectricity together with a deferred Td, the intrinsic formation mechanism of Td should be well understood. In this work, considering the role A-site cations play in manipulating the relaxor behavior of BNT, Pb2+, Ba2+, Sr2+, and Ca2+ (with distinguished ferroelectricity and polarity) are selected to investigate the formation mechanism of Td. Td reflects the stability of polarizations, which could be manipulated through modifying the polarization field and local electric and strain fields. The introduction of Pb2+ and Ba2+ increases the long-range correlated ferroelectric P4mm phase, which strengthens the polarization field and stabilizes polarizations, while the introduction of Sr2+ and Ca2+ increases the short-range correlated ferroelectric P4bm phase and the non-ferroelectric phase, which weakens the polarization field and destabilizes polarizations. Domain structures captured by a piezoresponse force microscope corroborate the effect of Pb2+ and Ba2+ in stabilizing polarizations and Sr2+ and Ca2+ in destabilizing polarizations. Therefore, by introducing the ferroelectric component that exhibits a different local symmetry to the BNT-matrix and can also provide a strong polarization field, the simultaneously enhanced piezoelectricity together with a deferred Td could be realized, as validated in the designed BNT-xPbTiO3 system. This work investigates the formation mechanism of Td and guides the design of high-performance systems in BNT-based materials, benefiting the understanding of BNT-based relaxor ferroelectrics.