Vanadium(II) oxide is the monoxide conventionally written . The name assigns formal oxidation state +2 to vanadium in the ideal one-to-one composition.
Real vanadium monoxide can be nonstoichiometric, with substantial lattice vacancies and composition-dependent ordering. Diffraction studies show that the distribution of occupied and vacant sites requires more information than a single ideal formula.[ref]
https://doi.org/10.1016/j.jallcom.2010.10.095. Abstract and experimental results: vacancy distribution in nonstoichiometric vanadium monoxide
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