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 (Tf) 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. The structural mechanism underlying the high piezoelectric activity of BF-BT was elucidated from the aspects of phase structure, domain dynamics, and octahedral torsion under an electric field.