Undoped and Hole-Doped Superconductors T$'$-La1.8-xEu0.2SrxCuO4 ($x = 0$ and 0.05) Prepared by Solid-State Reaction

We have successfully synthesized La 1.8-x Eu 0.2 Sr x CuO 4 ($x = 0$ and 0.05) with the Nd 2 CuO 4 -type (T$'$-type) structure by means of the structural transformation at low temperatures from the K 2 NiF 4 -type (T-type) structure via the Sr 2 CuO 3 -type (S-type) structure. Superconductivity has appeared by postannealing T$'$-La 1.8-x Eu 0.2 Sr x CuO 4 in vacuum at 700 °C for the removal of excess oxygen. The superconducting transition temperatures are 20 and 13 K for $x = 0$ and 0.05, respectively. T$'$-La 1.8-x Eu 0.2 Sr x CuO 4 with $x = 0.05$ is, at least nominally, the first hole-doped superconducting cuprate with the T$'$-type structure.