Effects of Ce addition on the crystal structure and superconductivity of high-entropy alloy Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6

High-entropy alloys (HEAs) consist of five or more principal elements with atomic fraction between 5 % and 35 %, randomly distributed throughout the lattice points. Recently, a simple body-centered cubic structure HEA superconductor, Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6, was discovered and classified as a type-II superconductor with a critical temperature of approximately 8 K. Ta-Nb-Hf-Zr-Ti HEA superconductors exhibit a large critical current density of 1 MA cm^-2 and demonstrate robust superconductivity against irradiation-induced disorder. We have synthesized HEA superconductors based on the composition Ta_1/6Nb_2/6Hf_1/6Zr_1/6Ti_1/6 with various Ce doping concentrations (0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 8 wt%), investigating the effects of Ce addition on the crystal structure and superconductivity. X-ray diffraction and energy dispersive x-ray spectroscopy results indicate the complex Ce addition effects on the crystals. Notably, while the superconducting transition temperature remains largely unaffected by the presence of magnetic impurities, it is found to be closely related to the lattice constant, which changes with varying Ce doping concentrations.