Relaxor-normal ferroelectric phase transition and significantly enhanced electromechanical strain behavior in Bi(Ni1/2Ti1/2)O3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary system close to the morphotropic phase boundary

A pseudo-cubic to tetragonal phase transformation was found to be accompanied by a relaxor-normal ferroelectric phase transition in new perovskite-type (0.65 − x)Bi(Ni1/2Ti1/2)O3–0.35PbTiO3–xPb(Mg1/3Nb2/3)O3 ceramics. A morphotropic phase boundary was identified in the range of 0.4 < x < 0.6 where the maximum quasi-static d33 = 550 pC/N was achieved. However, a large-strain platform of ∼0.35% was generated under 6 kV/mm (dynamic d33* = 583 pm/V) within 0.15 ≤ x ≤ 0.4. Particularly, the d33* and the strain hysteresis were found to be closely related with the Pb(Mg1/3Nb2/3)O3 content, field magnitude and signal frequency. The temperature-dependent measurement demonstrated that enhanced electrostrains appeared not only near a freezing temperature Tf, but also near an ergodic to ferroelectric phase transition temperature Tfr, both of which are ascribed to a reversible field induced ergodic to ferroelectric phase transition. An interesting finding would be that more similar free energies between ergodic and ferroelectric phases near Tfr have brought about smaller driving fields and strain hysteresis but lower maximum strains.