Computationally-driven discovery of a new weberite-type La₃NbO₇ antiferroelectric material

Antiferroelectricity, the property of materials to exhibit a double hysteresis loop in the polarization – electric field response as the result of the rearrangement of antipolar electric dipoles, is a rare phenomenon mostly associated with the perovskite structures. The energy landscape of an antiferroelectric is composed of an antipolar ground state, a polar structure slightly higher in energy, each originating from unstable phonon mode of a centrosymmetric phase.

In this presentation, I will discuss how this feature was used to search for new antiferroelectrics in a phonon database and identify a family with formula A₃MO₇  (M=Nb, Ta) as promising candidates. Our DFT calculations predict an antipolar ground state Pnma with a polar phase Cmc2₁ marginally higher in energy. The electric field-induced transition is associated with the displacements of the M atoms inside their oxygen octahedra. Further analysis, including energy barrier calculations and molecular dynamics simulations, indicated that La₃NbO₇ is the most promising candidate. Thin-films were grown via pulsed-laser deposition technique and characterized by transmission electron microscopy, confirming the antipolar ground state. Antiferroelectricity was then confirmed by conducting polarization versus electric-field and dielectric measurements on capacitor device structures. I will finish by discussing how this new material compare with the prototypical antiferroelectrics PbZrO₃ and NaNbO₃.