Switchable Polarization in an A-site Deficient Perovskite through Vacancy and Cation Engineering

TL;DR

This study demonstrates that defect engineering in an A-site deficient perovskite induces room-temperature ferroelectricity through vacancy and cation manipulation, offering a new approach to enhance polarization in improper ferroelectrics.

Contribution

It reveals a novel defect-ordering strategy to induce and enhance ferroelectricity in perovskites by controlling vacancies and cation arrangements, with potential for broad application.

Findings

Y$_{1/3}$TaO$_3$ exhibits room-temperature ferroelectricity.

Vacancy ordering enables net polarization despite local dipole cancellation.

Epitaxial strain can further enhance polarization.

Abstract

While defects are unavoidable in crystals and often detrimental to material performance, they can be a key ingredient for inducing functionalities when tailored. Here, we demonstrate that an A-site-deficient perovskite Y$_{1/3}$TaO$_3$ exhibits room-temperature ferroelectricity in a $Pb2_1m$ phase, enabled by ordered vacancies coupled with TaO$_6$ octahedral rotations. Defect-ordered perovskites are frequently trapped in centrosymmetric incommensurate states due to competing structural instabilities; we circumvent this by favoring rotational over polar instability through compositional selection. Unlike canonical improper ferroelectrics that are \textit{ferrielectric}, the vanishing dipoles on vacancy layers in Y$_{1/3}$TaO$_3$ allow for a net ferroelectric alignment of local dipoles, resulting in enhanced polarization. Upon heating, Y$_{1/3}$TaO$_3$ transforms to a paraelectric incommensurate phase at $\simeq$750 K, whose atomic arrangement mirrors the domain topology observed in hybrid improper ferroelectrics. Superspace analysis of the modulated phase reveals a route to improve room-temperature polarization, achieved through epitaxial strain, as confirmed by our lattice-dynamics calculations. This defect-ordering strategy should be generalizable to other improper ferroelectrics, including magnetoelectric multiferroics, providing a pathway to amplify otherwise limited macroscopic polarization.