Design of a multifunctional polar metal via first-principles high-throughput calculations*

Intrinsic polar metals are rare, especially in oxides, because free electrons screen electric fields in a metal and eliminate the internal dipoles that are needed to break inversion symmetry. The discovery of LiOsO₃ [Nat. Mater., 12, 1024 (2013)], a metal that transforms from a centrosymmetric R-3c structure to a polar R3c structure at 140 K, has stimulated an active search for new polar metals. In our recent study [Commun. Mater., 1, 1 (2020)], we use first-principles high-throughput calculations to predict a new polar metal BiPbTi₂O₆ and demonstrate 180^o electric-field switching of its polar displacements in its thin film form. Utilizing lone-pair electrons and different valences of Bi and Pb, we find that ordered BiPbTi₂O₆ can crystallize in three polar and conducting structures, each of which can be transformed to another via pressure or strain. In a heterostructure of layered BiPbTi₂O₆ and PbTiO₃, a strong interfacial coupling enables electric fields to first switch PbTiO₃ polarization and subsequently drive a 180^o change of BiPbTi₂O₆ polar displacements. Our work demonstrates the power of high-throughput screening in designing new functional materials and in particular predicts a new electrically switchable polar metal.