Niobium Monoxide Superstructures

The cubic and orthorhombic models of Nb 3 O 3 and Nb 6 O 6 superstructures of nonstoichiometric niobium monoxide Nb 0.75 O 0.75 with double defects have been proposed for the first time on the basis of the symmetry analysis and concepts of the channel of a disorder—order transition and the distribution function. The channel of the disorder—order transition associated with the formation of considered model superstructures includes three superstructure vectors, which are the arms k 10 (1) , k 10 (2) and k 10 (3) of the k 10 Lifshitz star. The distribution functions of O and Nb atoms over the sites of the Nb 3 O 3 and Nb 6 O 6 superstructures have been calculated. It has been shown that a decrease in the temperature can be accompanied by the formation of the Nb 3 O 3 cubic, Nb 3 O 3 orthorhombic, and Nb 6 O 6 orthorhombic phases through successive disorder—order and order—order transitions.