Superconducting properties ofBeB2.75

Abstract

We present the low-temperature electronic transport properties of the intermetallic commonly known as ${\mathrm{BeB}}_2.$ In contrast to the much simpler ${\mathrm{AlB}}_2$-type structure of the 39-K superconductor ${\mathrm{MgB}}_2,$ ${\mathrm{BeB}}_2$ forms a complex structure-type that is nearly unique in nature. The structure has 110.5 atoms per unit cell and a stoichiometry ${\mathrm{BeB}}_{2.75}.$ Polycrystalline $\mathrm{Be}{(}^{10.8}\mathrm{B}{)}_{2.75}$ is superconducting below $T_c=0.72\mathrm{}\hspace{0.5em}\mathrm{K}$ with a critical magnetic field $H_{c2\mathrm{}}=0.175\mathrm{}\hspace{0.5em}\mathrm{T}.$ Isotopically pure ${}^{10.0}\mathrm{B}$ samples have an enhanced $T_c=0.79\mathrm{}\hspace{0.5em}\mathrm{K}.$ Hall-effect measurements suggest that the material is intrinsically compensated.