Crystal and Magnetic Structures of New Tungsten Nitride Perovskite-related Materials

Nitride perovskites and related materials such as Ruddlesden-Popper (RP) layered nitrides are a recently discovered family of materials with exciting properties. Further exploration of W-based nitrides has led to two new materials that we propose to study here; the perovskite NdWN3 and the RP nitride Ce2WN4. Ce2WN4 crystallizes with a slight orthorhombic distortion of the tetragonal RP aristotype similar to the related material Ce2TaN4, where structural distortions originated from Ce3+/Ce4+ mixed valence. NdWN3 has an orthorhombic perovskite superstructure with octahedral tilt ordering (for the first time in this family). Rather surprisingly, the effective paramagnetic moment of Ce2WN4 indicates the presence of only one Ce3+/f.u., which indicates a mixed valent compound Ce3+Ce4+W5+N4, similar to Ce3+Ce4+Ta5+N4. At low temperatures, FC/ZFC measurements on Ce2WN4 indicate a Curie transition at TC ≈ 9 K with a saturated moment of ~1 μB/f.u. This could be consistent with ferrimagnetic order of up-Ce3+ and down-W5+ moments. Susceptibility measurements of NdWN3 (Fig. 2d) show paramagnetic behaviour of Nd3+ without magnetic ordering down to 2 K. We request 2 days of beamtime to study Ce2WN4 and NdWN3 on the WISH beamline at ISIS. Neutron diffraction is essential for crystal and magnetic structure determinations as well as confirming that such nitride perovskites are stoichiometric, oxygen-free, materials.