Stable antiferroelectricity with incompletely reversible phase transition and low volume-strain contribution in BaZrO3 and CaZrO3 substituted NaNbO3 ceramics

Abstract

In this work a reproducible double polarization versus electric field (P-E) hysteresis loop clearly reveals a room-temperature stable antiferroelectricity (AFE) in virgin NaNbO3 (NN) samples doped with 6 mol% BaZrO3 and 3 mol% CaZrO3. Inconsistent but sprout-like strain versus field (S-E) curves without any negative strains between the first and non-first cycles yet display an incompletely reversible field induced AFE-ferroelectric (FE) phase transition. In/ex-situ synchrotron x-ray diffraction results suggest irrecoverable AFE states with orthorhombic and monoclinic structures before and after electric cycling, respectively, which generate an irreversible strain contribution including both irreversible volume (22%) and lattice (78%) strains. Frequency-dependent measurements of P/S-E curves demonstrate the rest of remanent strains from the time effect of back-switching from field induced FE to AFE equivalently existing in strain loops of any cycles at a fixed frequency. Compared with virgin samples, post-cycled samples exhibit a completely reversible monoclinic AFE-monoclinic FE phase transition but a relatively small poling strain. It is of particular note that the contribution of the volume strain to the poling strain is only 20% in AFE NN-based ceramics, in which a positive longitudinal strain and a negative transverse strain are concurrently observed, challenging a common knowledge that both strains in two directions should be positive for traditional Pb-based AFE ceramics. The experimental results provide new insights into the AFE phase stability of NN and an exciting possibility to take advantage of NN-based antiferroelectric ceramics for large-displacement actuators in future.