Synthesis of new high-entropy alloy-type Nb3 (Al, Sn, Ge, Ga, Si) superconductors

•New high-entropy-alloy-type superconductors of Nb3M (M: Al, Sn, Ge, Ga, Si) were synthesized.•A superconducting transition at 11.0 K was observed for Nb3Al0.3Sn0.3Ge0.2Ga0.1Si0.1.•The HEA state in the M site of Nb3M results in a lower Tc. Studies on high-entropy alloy (HEA) superconductors have recently been increasing, particularly in the fields of materials science and condensed matter physics. To contribute to research on new HEA-type superconductors, in our study we synthesized polycrystalline samples of A15-type superconductors of Nb3Al0.2Sn0.2Ge0.2Ga0.2Si0.2 (#1) and Nb3Al0.3Sn0.3Ge0.2Ga0.1Si0.1 (#2) with an HEA-type site by arc melting. Elemental and structural analyses revealed that the compositions of the obtained samples satisfied the HEA state criteria. Superconducting transitions were observed at 9.0 and 11.0 K for #1 and #2, respectively, in the temperature dependence of magnetization and electrical resistivity. Specific heat measurements revealed that the Sommerfeld coefficient, Debye temperature, and ΔC/γTc for the obtained samples were close to those reported for conventional Nb3Sn family superconductors.