Effects of oxygen pressure on phase evolution and microstructural development in silver-clad (Bi,Pb)2Sr2Ca2Cu3O10+δ composite conductors

Abstract The kinetics of phase evolution and the development of microstructure in silver-clad composite conductors containing a Bi-Pb-Sr-Ca-Cu-O powder with a nominal stoichiometry of Bi 1.7 Pb 0.4 Sr 2 Ca 2 -Cu 3 O 10+δ were studied as a function of oxygen partial pressure ( pO 2 ), temperature, powder stoichiometry, and powder pre-treatment. The optimum temperature for growth kinetics of the Bi-2223 phase increased as the oxygen partial pressure was increased from 0.02 to 0.21 atm. The width of the phase stability region was largest for pO 2 = 0.075 atm and smallest for pO 2 = 0.21 atm. It was found that for a 25-h heat treatment, the reaction kinetics were the fastest in 0.075 atm of oxygen at temperatures between 825° and 830°C. The secondary phase particles (observed by scanning electron microscopy) were smaller for lower pO 2 (0.02 and 0.075 atm) than for higher pO 2 (0.13 and 0.21 atm).