Self-propagating high-temperature synthesis of cubic niobium nitride under high pressures of nitrogen

Cubic niobium nitrides δ-NbNx with different x = 0.87–1.015 were prepared by the self-propagating high-temperature synthesis (SHS) under nitrogen pressures of P(N2) = 48–230 MPa.Nitrogen composition x as a function of P(N2) was determined in weight gain experiments and compared with that determined by chemical (Kjeldahl) analysis. For powders with different x, the superconducting transition temperature Tc was measured as a function of lattice parameter a. The Tc values were found to grow linearly with increasing a. A maximum value of Tc = 15.0 K for cubic niobium nitride corresponded to a maximum value of a = 4.3901 Å.