New High Temperature Superconducting Oxides. (La1−xSrx)2CuO4−δ and (La1−xCax)2CuO4−δ

Solid solution systems of (La1−xSrx)2CuO4−δ and (La1−xCax)2CuO4−δ with x=0.05, 0.075, and 0.10 were found to exhibit the superconductivity through a.c. magnetic susceptibility and electrical resistivity measurements. The onset critical temperature for (La0.90Sr0.10)2CuO4−δ was 37 K, the highest among all the superconducting materials ever known, while that for (La0.95Ca0.05)2CuO4−δ was 18 K.