Niobium Monoxide Superstructures

Abstract

The cubic and orthorhombic models of Nb₃O₃ and Nb₆O₆ superstructures of nonstoichiometric niobium monoxide Nb_0.75O_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⁽¹⁾₁₀, k⁽²⁾₁₀ and k⁽³⁾₁₀ of the k₁₀ Lifshitz star. The distribution functions of O and Nb atoms over the sites of the Nb₃O₃ and Nb₆O₆ superstructures have been calculated. It has been shown that a decrease in the temperature can be accompanied by the formation of the Nb₃O₃ cubic, Nb₃O₃ orthorhombic, and Nb₆O₆ orthorhombic phases through successive disorder—order and order—order transitions.