Electric field induced irreversible change and asymmetric butterfly strain loops in Pb(Zr,Ti)O3-Pb(Ni1/3Nb2/3)O3-Bi(Zn1/2Ti1/2)O3 quaternary ceramics

The phase transformation and strain characteristics of (0.9-x)pb(Zr0.54Ti0.46)O-3-0.1Pb(Ni1/3Nb2/3)O-3-xBi(Zn1/2Ti1/2)O-3 (0.1PNN-(0.9-x)PZT-xBZT) solid-solution ceramics were investigated. The substitution of BZT for PZT can effectively decrease the sintering temperature from 1150 degrees C at x = 0-975 degrees C at x = 0.24. A typical morphotropic phase boundary (MPB) between ferroelectric rhombohedral (R) phases and relaxor tetragonal (T) phases was identified in the composition range of x = 0.12-0.18, resulting in enhanced dielectric, piezoelectric and electromechanical properties of d(33) = 610 pC/N, k(p) = 58% an epsilon(T)(33)/epsilon(o) = 2518 at x = 0.16. Most interestingly, exceptionally asymmetric butterfly strain loops were observed in the first-cycle electric loading, and found to obviously change with increasing the BZT content. The X-ray diffraction analysis on virgin and poled samples suggests that the observed asymmetric strain curves should stem from the electric field induced irreversible lattice shrinkage or lattice elongation in the single-R or single-T phase compositions, respectively. For MPB compositions, a combined effect of both opposite strain contributions would result in a maximum value (in absolute value) in the observed irreversible strain S-irr at x = 0.12, together with the effect of the electric field induced irreversible T-R phase transition. These results provide useful insights into the mechanism of forming asymmetric bipolar strains observed in BZT-substituted PZT-PNN piezoelectric ceramics.