  We have synthesized high-entropy-alloy-type (HEA-type) RE123 superconductors
Y0.28Nd0.16Sm0.18Eu0.18Gd0.20Ba2Cu3O7-d and
Y0.18La0.24Nd0.14Sm0.14Eu0.15Gd0.15Ba2Cu3O7-d with a superconducting transition
temperature (Tc) exceeding 90 K. From comparison between HEA-type and
conventional RE123 samples, we found that the mixing entropy at the rare earth
site does not affect Tc and critical current density (Jc) of the RE123 samples.
For all the examined samples, orthorhombicity was found to be an essential
parameter for Tc and Jc. In the regime near orthorhombic-tetragonal boundary,
Jc for the HEA-type sample was larger than that of conventional-type samples,
which suggests that HEA-type RE123 may be useful to improve Jc in the structure
with low orthorhombicity.
