Prediction of a native ferroelectric metal

TL;DR

This paper theoretically predicts a novel ferroelectric metal, Bi5Ti5O17, which uniquely exhibits native metallicity and switchable polarization in a single phase, challenging traditional distinctions between metals and ferroelectrics.

Contribution

First-principles calculations identify Bi5Ti5O17 as the first predicted material that is both metallic and ferroelectric with switchable polarization.

Findings

Bi5Ti5O17 has a non-zero density of states at the Fermi level.

Bi5Ti5O17 exhibits spontaneous polarization in zero field.

Polarization in Bi5Ti5O17 can be switched by an electric bias.

Abstract

The possibility that metals may support ferroelectricity is an open issue. Anderson and Blount showed that certain martensitic transitions involve inversion symmetry breaking and the formal existence of a polar axis, so 'metallic ferroelectric' behavior has been claimed for metals undergoing a centrosymmetric (CS) to non-CS structural transformation (Cd2ReO7, LiOsO3) or natively non-CS (SrCaRu2O), or for ferroelectric insulators whose polar distortion survives moderate metallicity induced by doping or proximity. However, none of these systems, nor any other to our knowledge, embodies a truly ferroelectric metal with native switchable polarization and native metallicity coexisting in a single phase. Here we report the first-ever theoretical prediction of such a material. By first-principles calculations, we show that the layered perovskite Bi5Ti5O17 has a non-zero density of states at the Fermi level and metal-like conductivity, as well as a spontaneous polarization in zero field. Further, we predict that the polarization of Bi5Ti5O17 is switchable both in principle, as the material complies with the sufficient symmetry requirements, and in practice, as Bi5Ti5O17 can sustain a sizable potential drop along the polar direction, as needed to revert its polarization by application of an electric bias.