Local Structure and Vacancy Distribution in Transition Metal Carbides: Results From High‐Resolution ¹³ C NMR Spectroscopy

Local structure, bonding, and the distribution of vacancies in stoichiometric and highly carbon‐deficient transition metal carbides (TMCs) ZrC, HfC, NbC, and TaC is studied using high‐resolution 13 C magic angle spinning (MAS) NMR spectroscopy. Isotopic enrichment of these TMCs with 13 C allows for remarkable signal enhancement and fast MAS of dielectric‐diluted samples, yielding high‐resolution NMR spectra of these TMCs for the first time. The 13 C MAS NMR spectra display positive correlation between the 13 C isotropic shift of the stoichiometric C site and the metal‐carbon nearest‐neighbor distance in these TMCs. More importantly, these spectra reveal the presence of multiple local carbon environments that can be attributed to either vacancies or oxygen and nitrogen impurities on the carbon sub‐lattice. Comparison between the NMR spectra of stoichiometric and highly carbon deficient TMCs shows that 13 C NMR can be used to differentiate between random distribution and clustering of vacancies and impurities in these lattices.