Synthesis of cerium oxynitride and oxoguanidinate at high pressures

Abstract

The pursuit of novel materials with tunable properties has driven significant interest in mixed-anion compounds, such as carbon nitrides and oxynitrides. In this study, we explored the Ce–O–N–C system under pressures of 35–55 GPa and temperatures of 1500–1800 K. The introduction of oxygen into the Ce–N system resulted in the formation of a novel oxynitride, Ce4O3N4, characterized by lower-order N–N bonding compared to the triple-bonded N2 molecule. In addition, we identified a new cerium oxoguanidinate, Ce2OCN3, in the Ce–O–C–N system. The crystal structures of Ce4O3N4 and Ce2OCN3 were determined using single-crystal x-ray diffraction, and their solutions were validated through Raman spectroscopy and density functional theory calculations. This experimental approach provides a robust method for investigating mixed-anion systems under high-pressure conditions. The identification of lower-bond-order nitrogen anions in oxynitride and guanidinate anions in oxoguanidinates highlights the potential for developing novel materials with unique properties based on mixed-anion species.