The composition/field-induced octahedral tilt, domain switching and improved piezoelectric properties of BF-BT ceramics during phase transition†

To clarify the structural mechanism underlying the high piezoelectric activity of (1 − x)BiFeO₃-xBaTiO₃ ((1 − x)BF-xBT) solid solutions, the evolution of phase structure and domain configuration and their effects on piezoelectric properties were studied in a wide range of components (0.2 ≤ x ≤ 0.9). XRD refinement results show that with the introduction of BT, the phase structure gradually transforms from rhombohedral (R) to rhombohedral/pseudocubic (R/pC) coexistence and finally to pC, accompanied by the weakening of lattice distortion. The freezing temperature (T_f) of (1 − x)BF-xBT decreases with the increment of BT around the morphotropic phase boundary (MPB) (0.3 ≤ x ≤ 0.5). This indicates that the domain structure changes from ferroelectric ordered domains to nanodomains (or polar nanoregions), corresponding to the enhancement of the relaxation state. The high piezoelectric properties of 0.7BF-0.3BT are attributed to the unique heterogeneous domain structure and superior domain switching at the MPB. A large strain is achieved in 0.6BF-0.4BT, which results from the mutual transformation between relaxor nanodomains and ferroelectric ordered domains under electric field.