Ferrielectricity in the Archetypal Antiferroelectric, PbZrO3
2Department of Physics, University of South Florida, Tampa, USA
3School of Mathematics and Physics, Queen's University Belfast, Belfast, UK
4School of Chemistry, University of St. Andrews, St. Andrews, UK
5G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, USA
PbZrO3 has been long considered as the archetypal antiferroelectric material – i.e., a material where the antipolar aligned dipoles can switch to a polar configuration under a high enough applied electric field, and return to the original antipolar state after its removal. Despite its historical prominence as the first discovered antiferroelectric and its role as the end member of the ubiquitous piezoelectric material lead zirconate titanate, there remain substantial controversies with respect to the ground state in this material. Specifically, the presence of a low-field, room temperature, ferroelectric phase has been often reported in PbZrO3 thin films, but assigned alternatively to surface reconstruction, Pb occupancy of the Zr lattice sites, residual stresses stabilizing a high or low temperature stable ferroelectric phase, etc.
We present a systematic report on ~200 nm thick (042)O and (001)O oriented films, where the ferroelectric phase is observed only in the former. Additionally, the films show substantial anisotropy in terms of the antipolar to polar and polar to antipolar transition fields (EAP→P and EP→AP, respectively). For example, EAP→P is ~350 kV/cm and ~620 kV/cm for the (042)O and (001)O films, respectively. The films also show extremely large strain under applied electric field (> 1%), and effective longitudinal piezoelectric coefficients of up to over 400 pm/V at the transition fields. Ultimately, we observe show “banded” modulations of polarization across the film thickness for the (001)O films, due to polarization direction changes in the in-plane (with respect to film’s surface) direction. Conversely, in the (042)O films the volumes of material with opposite relative polarization are intermixed, without a clear banding of similarly oriented dipoles. Based on these and additional functional and structural characterizations, consistent with theoretical models, we argue that the PbZrO3 films should be considered in a ferrielectric phase.
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