Comparative analysis of electromechanical performance of morphotropic phase boundary (MPB) based normal ferroelectric and non-MPB based relaxor ferroelectric perovskites

In the present work, we demonstrate that one can obtain comparable properties in composition far from Morphotropic phase boundary (MPB) by tuning the correlation length of polar-structural ordering in single phase relaxor ferroelectric perovskite. We examined this idea by a comparative structure-property analysis of a ferroelectric system (1-x) PbTiO3-(x)BiScO3 (PT-BS) (d(33) similar to 500 pC/N at MPB) and a non-MPB (1-x)PbTiO3-(x)Bi(Ni1/2Hf1/2)O-3 (PT-BNH) system (d(33) similar to 425 pC/N at pseudo-MPB). Structural analysis of x-ray powder diffraction (XRPD) data of MPB (x = 0.3725) composition of (1-x) PbTiO3-(x)BiScO3 (PT-BS) shows tetragonal + rhombohedral/monoclinic phase co-existence and there is a increment in tetragonal structural phase fraction at the cost of rhombohedral phase after poling, resulting in large piezoelectric property. On the other hand XRPD data of pseudo-MPB (x = 0.39) composition of (1-x)PbTiO3-(x)Bi(Ni1/2Hf1/2)O-3 (PT-BNH) shows cubic like (CL) + tetragonal phase co-existence and tetragonal structural phase fraction increases at the cost of co-existing cubic like phase upon poling, giving rise to the piezoelectric property comparable to that of MPB PT-BS. Raman spectra and x-ray pair distribution analysis show cubic like phase, which is the manifestation of miniaturized domains with tetragonal symmetry and its correlation length increases upon poling. Our analysis suggests that increased polar-structure heterogeneity at the non-MPB composition can result in large piezoelectric response and requirement of a MPB composition is not a necessary criterion to obtain enhanced electromechanical property.