Electric field induced phase transition and accompanying giant poling strain in lead-free NaNbO3-BaZrO3 ceramics

A series of phase transitions in (1-x)NaNbO3-xBaZrO3 ((1-x)NN-xBZ) ceramics was observed from antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase and finally into ferroelectric rhombohedral phase with increasing x. An electric field induced irreversible phase transition was found in different compositions, irrespective of their virgin phase structures. Particularly, an antiferroelectric orthorhombic phase is irreversibly transformed into a ferroelectric monoclinic phase within 0.02 ≤ x ≤ 0.05, leading to a giant poling strain of ∼0.58%. This is much larger than that observed in ferroelectric orthorhombic (0.06 ≤ x ≤ 0.07) and rhombohedral phases (0.08 ≤ x ≤ 0.11) suffering from an irreversible ferroelectric-ferroelectric (monoclinic) phase transition. The synchrotron x-ray diffraction and the measurement of longitudinal and transverse strains suggest that this irreversible phase transition should involve not only a distinct volume expansion, but also an obvious lattice elongation. The present study demonstrates a unique nature of the composition and field dependent phase stability and an underlying mechanism of giant poling strains in NN-BZ ceramics.