Preparation of Bulk‐Phase Nitride Perovskite LaReN 3 and Topotactic Reduction to LaNiO 2 ‐Type LaReN 2

While halide and oxide perovskites are numerous and many display outstanding properties, ABN 3 perovskite nitrides are extremely rare due to synthetic challenges arising from the low chemical potential of nitrogen and a tendency to form low‐coordination nitridometallate anions. We report the preparation of a perovskite nitride LaReN 3 through azide‐mediated oxidation at high pressure. High‐resolution synchrotron diffraction shows that LaReN 3 has a low‐symmetry, triclinic, perovskite superstructure resulting from orbital ordering with strong spin‐orbit coupling distortions. Topotactic reduction of LaReN 3 above 500 °C leads to layered tetragonal LaReN 2 via a probable LaReN 2.5 intermediate, which is the first reported example of nitride defect perovskites. Magnetisation and conductivity measurements indicate that LaReN 3 and LaReN 2 are both metallic solids. The two chemical approaches presented are expected to lead to new classes of ABN 3 and defect ABN 3− x nitride perovskite materials.