Annealing effects on the Pb-doped 2223 phase under various temperatures and oxygen pressures

Abstract Annealing effects on the Pb doped 2223 type superconductor Pb 0.35 Bi 1.73 Sr 1.89 Ca 1.86 Cu 3.0 O y at various temperatures (200– 800°C) and oxygen pressures ( P O 2 =0.2–500 atm and in vacuum) are reported. XRD, SEM and TEM examinations indicated that the annealing below 800°C under oxidizing atmosphere generally brought about a segregation of a Ca 2 PbO 4 -like phase and (Sr,Ca) 2 CuO 3 on the surface of the original particles. The particles of the 2223 phase kept their shape and remained well-crystallized but changed to a lead-poor or lead-free composition as seen from a change in the structural modulation wave length from 47 A to 27 A. These results have strongly suggested that these two modulation modes correspond to different chemical compositions, one rich in Pb as Pb/Bi≅ 1 5 and the other Pb free, Pb/Bi≅0. Under P O2 ⪖100 atm at 300°C the oxygen content in the remaining 2223 phase seemed to have increased as suggested from a contraction of the c -axis. When the annealing temperature was raised to 600°C at P O 2 =100 atm, a complete decomposition to a perovskite phase, (Sr,Ca) (Pb,Bi)O 3 , CuO and Ca 2 PbO 4 occurred surprisingly. Under reduced oxygen pressures, the precipitation did not occur.