Annealing of pressure-induced structural damage in superconducting Bi–Pb–Sr–Ca–Cu–O ceramic

Abstract

Ac susceptibility measurements have been used to monitor the changes in the superconductive properties of sintered and uniaxially pressed samples of Pb-stabilized 2223-phase bismuth cuprate ceramic as the structural damage was annealed in air in a sequence of steps in temperature between 500 and 850 °C. It is concluded that below 600 °C a relaxation of residual stresses is responsible for a 2% shrinkage in sample volume and a small improvement in bulk superconductive transition temperature, T_c. Above 700 °C, a recovery of the original properties occurs through grain regrowth governed by an activation energy of ∼200 kJ/mol. However, in the region between 600 and 700 °C, a decrease in T_c of ∼40 K appears to be the result of plastic flow and amorphization associated with local decomposition of 2223 which reduces the effective grain size and weakens the intergranular superconductive coupling.