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 Tc 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 ΔSmix = 1.60R 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 Uiso 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.

Axis thermal expansion switching in transition-metal zirconides TrZr2 by tuning the c/a ratio

“…[13][14][15][16] Recently, transition-metal zirconides CoZr 2 and alloyed TrZr 2 (where Tr denotes Fe, Co, Ni, Rh and Ir) have been reported as a new family of NTE compounds. 17,18) The crystal structure of TrZr 2 is depicted in Fig. 1(a), which is a body-centered tetragonal structure of CuAl2-type, in space group #140.…”

“…3 illustrates the temperature dependence of the change ratio of lattice constants in the a-axis (Δa/a = 1 − a(300 K)/a(T)), c-axis (Δc/c = 1 − c(300 K)/c(T)) and volume (ΔV/V = 1 − V(300 K)/V(T)) normalized at room temperature of TrZr 2 (Tr = Ni, Co, (Fe, Co,Ni), (Co,Rh,Ir), (Fe,Co,Rh,Ir), (Fe,Co,Ni,Rh,Ir), (Co,Ni, Cu,Rh,Ir), (Fe,Co,Ni,Cu,Ga)). 17,18) Table I summarizes the linear TEC of these materials, calculated using Eq. ( 1).…”