High-pressure synthesis of Ruddlesden-Popper nitrides.

Layered perovskites with Ruddlesden-Popper-type structures are fundamentally important for low-dimensional properties, for example, photovoltaic hybrid iodides and superconducting copper oxides. Many such halides and oxides are known, but analogous nitrides are difficult to stabilize due to the high cation oxidation states required to balance the anion charges. Here we report the high-pressure synthesis of three single-layer Ruddlesden-Popper (K 2 NiF 4 type) nitrides-Pr 2 ReN 4 , Nd 2 ReN 4 and Ce 2 TaN 4 -along with their structural characterization and properties. The R 2 ReN 4 materials (R = Pr and Nd) are metallic, and Nd 2 ReN 4 has a ferromagnetic Nd 3+ spin order below 15 K. Thermal decomposition gives R 2 ReN 3 with a Peierls-type distortion and chains of Re-Re multiply bonded dimers. Ce 2 TaN 4 has a structural transition driven by octahedral tilting, with local distortions and canted magnetic Ce 3+ order evidencing two-dimensional Ce 3+ /Ce 4+ charge ordering correlations. Our work demonstrates that Ruddlesden-Popper nitrides with varied structural, electronic and magnetic properties can be prepared from high-pressure synthesis, opening the door to related layered nitride materials.