Abstract
Lead zirconate (PbZrO3) is considered the prototypical antiferroelectric material with an antipolar ground state. Yet, several experimental and theoretical works hint at a partially polar behaviour in this compound, indicating that the polarization may not be completely compensated. In this work, we propose a simple ferrielectric structure for lead zirconate. First-principles calculations reveal this state to be more stable than the commonly accepted antiferroelectric phase at low temperatures, possibly up to room temperature, suggesting that PbZrO3 may not be antiferroelectric at ambient conditions. We discuss the implications of our discovery, how it can be reconciled with experimental observations and how the ferrielectric phase could be obtained in practice.
Highlights
Lead zirconate is often considered the prototypical antiferroelectric material and was the first compound identified as such[1]
We compare the relative energies of the FiE phase with those of (i) the commonly accepted ground state (AFE40), (ii) an antipolar phase obtained from a soft-mode condensation of AFE40 (AFE80)[15], which presents space group Pnma, and (iii) a low-energy ferroelectric phase with R3c symmetry (‘FE’ in the following). (This FE phase is the ground state of BiFeO3 and features a spontaneous polarization along the [111] direction and an a−a−a− oxygen octahedra tilt pattern in Glazer’s notation30.) We find that the four studied polymorphs lie within an energy range of ~1 meV per f.u., the phase hierarchy being, from most to least stable, AFE80, FiE, AFE40 and FE
Do our results offer any information about this intermediate phase? On the one hand, the results obtained with local density approximation (LDA) and PBEsol seem to rule out the rhombohedral FE state here considered as a possible candidate, as the computed free energies are much higher than those of competing polymorphs
Summary
Lead zirconate is often considered the prototypical antiferroelectric material and was the first compound identified as such[1]. A recent work[15] predicted from first-principles a new ground state for PbZrO3, characterized by a small cell-doubling distortion of the AFE40 state but retaining the same antipolar pattern (‘AFE80’ in the following). Previous theoretical works on PbZrO3 have reported polar polymorphs[11,13,14] lying at relatively low energies, and antipolar polymorphs with longer period modulations than the AFE40 phase have been found. Polar antiphase boundaries have been often reported and studied in PbZrO32,22–28 These results suggest that the AFE40 phase (or, for that sake, the recently proposed AFE80), might not be the ground state of this compound. We introduce a simple ferrielectric phase for
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