A search for superconductivity below 1 k in transition metal borides

Abstract We examined some AlB 2 -type ( C 32 structure) boron compounds for superconductivity down to 0.42 K; the compounds have the formula MeB 2 (MeTi,Zr,Hf,V,Nb,Ta,Cr,Mo) (the atomic ratio of metal to boron was 0.5). Only NbB 2 was found to be superconducting with T c = 0.62 K and a surprisingly high value of H c (0), about 1600 Oe. Other transition metal as well as non-transition metal boron phases were also tested for superconductivity down to 0.42 K; these compounds were MeB 6 (MeCa,Sr,Ba), W 2 B 5 , CrB, Cr 5 B 3 , UB 2 , UB 4 and UB 12 . None of these compounds proved to be superconducting above 0.42 K; nor was any trace of superconductivity down to 0.42 K observed in MoB and NbB.