Triple-point-type morphotropic phase boundary based large piezoelectric Pb-free material—Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3

We report a large piezoelectric Pb-free system—Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3, designed upon a triple-point morphotropic phase boundary (TMPB) idea. The system shows anomalies of both ac (dielectric and piezoelectric) and dc (P-E hysteresis) properties around TMPB, especially the d33 achieving ∼550 pC/N at room temperature. Moreover, the detected non-zero thermal hysteresis around triple point shows a first order transition nature and non-isotropic polarization state, as well as verified by our theoretical Landau-type deduction, thus being considered as an important factor to influence the piezoelectricity along TMPB. Our work may stimulate the study on triple-point-related critical phenomena in other ferroic systems.