Prediction of a native ferroelectric metal

Over 50 years ago, Anderson and Blount discussed symmetry-allowed polar distortions in metals, spawning the idea that a material might be simultaneously metallic and ferroelectric. While many studies have ever since considered such or similar situations, actual ferroelectricity—that is, the existence of a switchable intrinsic electric polarization—has not yet been attained in a metal, and is in fact generally deemed incompatible with the screening by mobile conduction charges. Here we refute this common wisdom and show, by means of first-principles simulations, that native metallicity and ferroelectricity coexist in the layered perovskite Bi 5 Ti 5 O 17 . We show that, despite being a metal, Bi 5 Ti 5 O 17 can sustain a sizable potential drop along the polar direction, as needed to reverse its polarization by an external bias. We also reveal striking behaviours, as the self-screening mechanism at work in thin Bi 5 Ti 5 O 17 layers, emerging from the interplay between polar distortions and carriers in this compound. Ferroelectricity, spontaneous switchable polarization, is usually deemed incompatible with the electronic screening of a metal. Here, the authors use ab initio theory to predict that metallicity natively coexists with ferroelectric polarization and finite depolarizing fields in the perovskite Bi 5 Ti 5 O 17 .