Superconductivity in WBe2

Abstract

WBe₂, which occurs in space group 194, with hexagonal symmetry P6₃/mmc, is prepared by arc-melting at temperatures above 2200 C, where Be vapor loss is significant. This study is motivated by recent work on MoB₂ and WB₂, both superconductors (T_c=32 and 17 K respectively) under high (~70 GPa) pressure. In order to avoid the known Be-rich superconducting phases (WBe₁₃ and WBe₂₂) in the complex phase diagram, both known to be superconducting at 4.1 K, the sample was prepared with a slight (~5%) excess of W. The resultant sample, prepared using high purity (99.999%) Be, is essentially single phase WBe₂, with some spread in its superconducting properties due to the known homogeneity range. (WBe₂ forms in space group 194 between approximately W_1.02Be_1.98 and W_0.88Be_2.12.) Characterization was carried out with x-ray diffraction, electrical resistivity, ρ, in zero and applied magnetic fields, and specific heat. The resistivity in zero and applied fields and specific heat data indicate that our sample of WBe₂ is a bulk superconductor at ambient pressure with a T_c^onset in ρ at 1.05 K, and T_c(ρ→0) at ~0.86 K. There is no signature of superconductivity in ρ at 4.1 K, indicating successful avoidance of WBe₁₃ and WBe₂₂. The ρ data in field indicate an upper critical field of approximately 400 gauss.