Reversible Phase Transition of the Bi-Ca-Sr-Cu-O System between Semiconductivity and Superconductivity

Abstract
Alternative quenching from higher temperature with liq. nitrogen and annealing at lower temperature exhibit a reversible phase transition from semiconductivity to superconductivity in the Bi-Ca-Sr-Cu-O system. The thermally treated specimens were characterized by means of X-ray diffraction (XRD). The specimens quenched from above 900°C were found to be semiconducting, and were converted into superconducting after being annealed at 820°C for 40h under O2 atmosphere. The annealed samples had two norminal compositions corresponding to Tc,onset=150K and Tc,zero=90K for BiCaSrCu2O x and Tc,onset=125K and Tc,zero=84K for Bi4Ca3Sr3Cu4O x .