Oxidation-resilient superconductivity in a novel high-hardness superconductor: a first-principles study

Niobium nitride (NbN) is a crucial superconducting material that has been extensively studied and utilized. Enhancing the working temperature and environmental stability of devices fabricated from this material is a significant research focus. In this study, we employed first-principles computational methods to comprehensively investigate the superconducting, mechanical, and electronic properties of CsCl-type NbN. Our results reveal that this type of superconducting material exhibits a high superconducting transition temperature (<i>T</i>_c) of up to 16 K along with exceptional hardness. Under high pressure conditions, the phonons undergo gradual hardening, leading to a decrease of <i>T</i>_c. However, when oxidized, its superconductivity not only persists but also there is even an increase of <i>T</i>_c. This phenomenon is attributed to the electron doping effect caused by oxygen substitution for nitrogen, which shifts the Fermi level closer to the van Hove singularity. Our findings present a promising candidate for further experimental exploration.