INCOMMENSURATE ORDERED PHASE IN NONSTOICHIOMETRIC TANTALUM CARBIDE

By the neutron diffraction structure analysis method, an ordered phase of non-stoichiometric tantalum carbide TaCy with the base B1(NaCl) st ructure has been detected. It is shown that the superstructural reflec tions observed correspond to an incommensurate superstructure close to M(6)C(5) type. With allowance for ordering of TaCy, the phase diagram of the Ta-C system has been calculated and constructed. The effects o f non-stoichiometry and ordering on the period of a base B1-type latti ce of tantalum carbide and on the superconducting critical temperature have been studied.