Preparation of disordered and ordered highly nonstoichiometric carbides and evaluation of their homogeneity

Abstract

The features of solid-phase synthesis of highly nonstoichiometric carbides with controlled concentration of structural vacancies in the carbon sublattice have been considered. Four main stages are distinguished in the synthesis of nonstoichiometric carbides by the solid-phase sintering technique. It is shown that the inhomogeneity of highly nonstoichiometric compounds leads to the broadening of diffraction reflections. The analytical relation between the broadening and the inhomogeneity is obtained for the first time, and the method based on diffraction measurements is proposed for the quantitative evaluation of the degree of homogeneity of nonstoichiometric compounds. As an illustration of the advanced approach, the degree of homogeneity of nonstoichiometric niobium carbide is evaluated from the experimental data on the width of x-ray diffraction peaks. The heat treatment conditions providing the preparation of nonstoichiometric Group IV and V transition metal carbides in the disordered and ordered states are determined.