High-Tc Superconductivity in La-Ba-Cu-O and Y-Ba-Cu-O Compounds

A high-critical-temperature superconducting transition in multiple-phase La-Ba-Cu-O and Y-Ba-Cu-O systems has been found with the aid of electrical and magnetic measurements. The possible causes of superconductivity is also considered. Among them the change of Fermi-surface topology is the most appreciated.