  Single-crystal whiskers of REBa2Cu3Ox (RE-123, RE: rare earth element)
cuprate superconductors were successfully grown using Te-doped precursors
utilizing the concept of high-entropy-alloys (HEAs) at the RE site. The
obtained whiskers were 0.5-1.0 mm length with approximately 10 um thickness.
The width of the flat surface, which corresponds to the ab-plane, was 10-50 um.
The RE site of the grown whiskers could be easily substituted by large ionic
radius RE elements (Gd, Dy, and Ho). Substitution with small ionic radius RE
elements (Tm, Yb, and Lu) resulted in the opposite trend. The superconducting
transition temperature and superconducting anisotropy of the grown RE-123
whiskers were 89-93 K and 6-10, respectively. The mixed entropy at the RE site
in the RE-123 whiskers did not affect the superconducting transition
temperature and superconducting anisotropy.
