Resistivity anomaly in the high-temperature superconductor Bi-Sr-Ca-Cu-O

An anomalous resistance drop was observed near 190K in the R-T measurement on a sample in Bi-Sr-Ca-Cu-O system and the transition completed at 80K. After keeping the sample at room temperature for 10h, the temperature dependence of the resistance changed from semiconducting to metallic behavior, while the ending of the transition remained at 80K. This might be an evidence of the existence of a metastable superconducting phase in Bi-Sr-Ca-Cu-O system with Tc as high as 190K.