Co-existence of 3 classes of phase-transition up to 90K including superconductivity in La2−x CuO4−y system

Abstract For investigation of the oxide superconducting mechanism, a most simple system; La 2−x CuO 4−y was adopted and multistage phase transitions; including two classes superconducting of Tc 1 =10−11K, Tc 2 =35−40K and a diamagnetic transition of Tc 3 =85−91K were observed in susceptibility and resistivity measurements up to about 90K. The atmospheric oxygen pressure during the sample heat treatment turns out to be essential for those transition-phase growth.