Phase transitions and the piezoelectricity around morphotropic phase boundary in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 lead-free solid solution

In this paper, two displacive phase transitions around the morphotropic phase boundary (MPB) in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) ceramics were detected by inspecting two anomalies of the Raman Ti4+-O2− longitudinal optical mode (∼725 cm−1). Further, permittivity and X-ray diffraction results demonstrated these two phase transitions originate from tetragonal (T) to rhombohedral (R) through an intermediate orthorhombic (O) phase. Importantly, we found that the maximum piezoelectric response (d33 = 545pC/N) was achieved at the boundary between the T and O phase, indicating that the giant piezoelectricity of BZT-xBCT may mainly stem from the T-O phase boundary due to easier polarization rotation and larger lattice softening.