THE EFFECTS OF ATOMIC AND VACANCY ORDERIN G IN NONSTOICHIOMETRIC CARBIDES

An analysis of the electronic structure of highly nonstoichiometric tr ansition-metal carbides in both ordered and disordered states is given , which explains the influence of atomic and vacancy order on the phys ical properties of the carbides. It is shown that the dependence of ca rbide properties on the arrangement of carbon atoms on the nonmetal su blattice is related to both the crystal symmetry space group and the s ymmetry of the nearest-neighbour environment of the carbid atoms. By c onsidering order-disorder phase transition data, experimental informat ion on atomic and vacancy order in carbides is obtained in order to ex plain the nature of superstructures al high vacancy concentrations.