Incommensurate ordered phase in non-stoichiometric tantalum carbide

By the neutron diffraction structure analysis method, an ordered phase of non-stoichiometric tantalum carbide TaCy with the base B1(NaCl) structure has been detected. It is shown that the superstructural reflections 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 of non-stoichiometry and ordering on the period of a base B1-type lattice of tantalum carbide and on the superconducting critical temperature have been studied.