Preparation of bulk-phase nitride perovskite LaReN3 and topotactic reduction to LaNiO2-type LaReN2.

Abstract

While halide and oxide perovskites are numerous and many display outstanding properties, ABN 3 perovskite nitrides are extremely rare due synthetic challenges arising from the low chemical potential of nitrogen and a tendency to form low-coordination nitridometallate anions. Here 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, the first reported examples of nitride defect-perovskites. Magnetisation and conductivity measurements indicate that LaReN 3 and LaReN 2 are both metallic solids. The two chemical approaches presented here are expected to lead to new classes of ABN 3 and defect ABN 3-x nitride perovskite materials.