Degradation by Mechanical Grinding and Recovery by Annealing in the Superconducting Phases of the Bi-Pb-Sr-Ca-Cu-O System

Abstract

It has been found that mechanical grinding may severely degrade phases from the superconducting to nonsuperconducting; i.e., a sample with 73 vol% of the high- T c phase (105 K phase), 18 vol% of the low- T c phase (75 K phase) and 8 vol% of a nonsuperconducting phase resulted in a sample with 98 vol% of a nonsuperconducting amorphous phase after grinding for 62 min. Susceptibility analysis showed that the high- T c phase changed into a nonsuperconducting amorphous phase more easily than the low- T c phase by mechanical grinding. It was also found that the degraded sample did not recover easily to the initial state compared with another kind of amorphous sample which was prepared by melt quenching and was initially free of the high- T phase. A process which includes such a crystal grinding causing the degradation of the superconducting phases may not therefore be appropriate for fabricating practical superconducting wires or sheets.