Superconductivity of high-entropy-alloy-type transition-metal zirconide (Fe,Co,Ni,Cu,Ga)Zr2

Abstract

We synthesized a new high-entropy-alloy-type (HEA-type) superconductor (Fe,Co,Ni,Cu,Ga)Zr2 with a T c of 2.9 K. The EDX analyses revealed that the actual composition of the transition-metal site (Tr-site) is Tr = Fe0.17(1)Co0.18(2)Ni0.21(2)Cu0.25(1)Ga0.19(1), which gives the configurational entropy of mixing ΔS mix = 1.60 R for the Tr site. Neutron powder diffraction revealed that the sample has a tetragonal CuAl2-type (space group: #140). The lattice constant of a monotonically decreases with decreasing temperature, but the lattice constant of c does not exhibit a clear shrinkage. Isotropic displacement parameter for both the Tr and Zr sites are large, which is probably caused by the HEA-type Tr site. The small temperature dependences of U iso for both sites also indicate the presence of the local structural disorder in (Fe,Co,Ni,Cu,Ga)Zr2. From electrical resistivity, magnetic susceptibility, and specific heat measurements, bulk superconductivity was confirmed.