Observation of thermally stable polar metallic state in perovskite nitride CeWN3.

Polar metals offer substantial potential for exotic quantum phenomena and multifunctional applications. However, the existence of a polar metal is fundamentally challenging owing to the screening of dipole-dipole interactions by conducting electrons. Specifically, a high-temperature-stabilized polar metal remains to be discovered. In this study, we report a thermally stable polar-metal state in perovskite cerium tungsten nitride. Synchrotron x-ray diffraction and electron microscopy reveal a polar Pna21 structure, while second-harmonic generation demonstrates that the polar response persists up to 850 kelvins in argon. Electrical resistivity and optical conductivity measurements demonstrate metallic transport behavior, consistent with the itinerant electronic contribution derived from specific heat analysis. First-principles calculations reveal that the polar distortion and metallic conductivity originate from tungsten-centered nitrogen octahedra, where the off-center displacements of hexavalent tungsten ions govern polarity and hybridization between tungsten 5d and nitrogen 2p states contributes to itinerant carriers. This study establishes a record-high-temperature polar metal, opening a promising avenue for exploring robust polar and metallic materials in perovskite nitrides.