Annealing effect on the irreversibility line in (Cu,C)Ba 2Ca 2Cu 3O y

Abstract

Annealing effects on irreversibility fields ( H irr) and physical properties in high-quality (Cu,C)Ba 2Ca 2Cu 3O y ((Cu,C)-1223) samples have been investigated. The T c of (Cu,C)-1223 increased from 70 K (as-prepared) to 120 K by annealing up to 550 °C in a nitrogen gas. The decomposition temperature (≃550°C) and the annealing effect on T c of (Cu,C)-1223 were found to be different from that in C-free samples, which may be due to stability of carbonates in the (Cu,C)-site. The slightly overdoped sample ( T c =111 K ) showed high H irr (=9.4 T) at 77 K rather than the optimal-doped sample ( T c =120 K ). This indicates that control of doping level as well as T c is important to enhance the H irr at 77 K.