Superconducting phase in niobium diborides prepared by combustion synthesis

A metastable superconducting phase in niobium diborides has been formed by a combustion-synthesizing process. It has been reported that stoichiometric NbB 2 shows no superconductivity down to a temperature of 1.8 K. However, a superconducting phase with a transition up to 8 K in the composition of Nb x B 2 ( x=0.67–1.11) was induced by combustion synthesis. This superconducting phase is recognized as the same metastable one found in our previous work by a rapid-quenched process. The superconducting properties and the lattice parameters of Nb x B 2 formed by combustion synthesis are compared with those formed by the conventional arc-melting process.