SEARCH FOR SUPERCONDUCTIVITY BELOW 1-K IN TRANSITION-METAL BORIDES

We examined some AlB2-type (C32 structure) boron compounds for superconductivity down to 0.42 K; the compounds have the formula MeB2(MeTi,Zr,Hf,V,Nb,Ta,Cr,Mo) (the atomic ratio of metal to boron was 0.5). Only NbB2 was found to be superconducting with Tc = 0.62 K and a surprisingly high value of Hc(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 MeB6 (MeCa,Sr,Ba), W2B5, CrB, Cr5B3, UB2, UB4 and UB12. 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. © 1979.