STABILITY AND GROWTH OF THE (BI,PB)2SR2CA2CU3OX PHASE IN A SILVER SHEATH

The chemical stability and growth kinetics of the (Bi,Pb)2Sr2Ca2Cu3Ox (2223) phase have been investigated as a function of temperature and c omposition using x-ray diffraction, scanning electron microscopy and w avelength dispersive x-ray spectroscopy. Silver tubes were filled with precursor 2223 powders and processed into tapes using conventional de formation techniques. The tapes were processed at temperatures ranging from 810 to 830-degrees-C for times ranging from 10 to 12,000 minutes in an oxygen partial pressure of 0.075 atm. The 2223 phase shows limi ted non-stoichiometry of Cu, (Ca+Sr), and (Bi+Pb), but relatively broa d solid solubility within the alkaline earths and heavy metals. The ki netics of transformation from Bi2Sr2Ca1Cu2Ox to the 2223 phase appear to be controlled by a two-dimensional diffusion process.