Understanding the structural mechanism of electric properties in xBiFeO3-(1-x)BaTiO3 lead-free piezoelectric solid solutions

Chemical distributions, local phase and domain configurations of xBiFeO3-(1-x)BaTiO3 (BF-BT) ceramics with different macroscopic phases were carefully studied to understand the structural mechanisms of electric properties. Universal BF-rich@BT-rich@average-composition triple core-rim structures were found to exist in all the compositions, and the volume fractions of cores decrease with the BF content. The inner cores all show dominant rhombohedral (R) phase, while the rims change from dominant pseudo-cubic (PC) phase with polymorphic polar nanoregions (PNRs) (x = 0.64) to coexistence of R and PC with PNRs and nanodomain (x = 0.7) and then to dominant R phase with PNRs+macrodomain (x = 0.75). The high densities of phase and domain boundaries are responsible for the high and thermal-stable electric-field induced strain in the PC phase. Our results evidence the decisive contribution of the composition-modulated hierarchical microstructures to the electric-field induced strain, and are anticipated to provide the necessary foundation for the effective modulation of the piezoelectricity.