  Since the discovery of superconductivity in a high-entropy alloy (HEA)
Ti-Zr-Nb-Hf-Ta in 2014, the community of superconductor science has explored
new HEA superconductors to find the merit of the HEA states on superconducting
properties. Since 2018, we have developed HEA-type compounds as superconductors
or thermoelectric materials. As well known, compounds like intermetallic
compounds or layered compounds are composed of multi crystallographic sites. In
a HEA-type compounds, one or more sites are alloyed and total mixing entropy
satisfies with the criterion of HEA. Herein, we summarize the synthesis
methods, the crystal structural variation and superconducting properties of the
HEA-type compounds, which include NaCl-type metal tellurides, CuAl2-type
transition metal zirconides, high-Tc cuprates, and BiS2-based layered
superconductors. The effects of the introduction of a HEA site in various kinds
of complicated compounds are discussed from the structural-dimensionality
viewpoint.
