High-pressure synthesis of an oxynitride perovskite CeNbO₂N with Nb⁴⁺ charge state

Perovskite oxynitrides AB(N,O)₃, a crucial class in materials science, have attracted much attention. By precisely controlling A- and B-site ions and tuning the N/O ratio, new materials with exotic charge states and intriguing electronic behaviors can be designed and synthesized. In this work, a novel oxynitride perovskite, CeNbO₂N, was prepared under high-temperature and high-pressure conditions. The compound crystallizes in an orthorhombic perovskite structure in Pnma symmetry with disordered N/O distribution. The x-ray absorption spectroscopy confirms the presence of a Nb⁴⁺ state with 4d¹ electronic configuration in CeNbO₂N. As a result, the resistivity of CeNbO₂N is sharply reduced compared to its counterpart CeTa⁵⁺ON₂ and other Nb⁵⁺ compounds. No long-range spin order is found to occur with the temperature down to 2 K in CeNbO₂N, while a remarkable negative magnetoresistance effect shows up at lower temperatures, probably due to the magnetic scattering arising from short-range spin correlations.