Preparation of Bulk-Phase Nitride Perovskite LaReN3 and Topotactic Reduction to LaNiO2 -Type LaReN2.

While halide and oxide perovskites are numerous and many display outstanding properties, ABN3 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 LaReN3 through azide-mediated oxidation at high pressure. High-resolution synchrotron diffraction shows that LaReN3 has a low-symmetry, triclinic, perovskite superstructure resulting from orbital ordering with strong spin-orbit coupling distortions. Topotactic reduction of LaReN3 above 500 °C leads to layered tetragonal LaReN2 via a probable LaReN2.5 intermediate, which is the first reported example of nitride defect perovskites. Magnetisation and conductivity measurements indicate that LaReN3 and LaReN2 are both metallic solids. The two chemical approaches presented are expected to lead to new classes of ABN3 and defect ABN3-x nitride perovskite materials.