PHASE-STABILITY, OXYGEN NONSTOICHIOMETRY, AND SUPERCONDUCTIVITY PROPERTIES OF BI2SR2CACU2O8+DELTA AND BI1.8PB0.4SR2CA2CU3O10+DELTA

Phase stability of Bi2Sr2CaCu2O8+delta (2212) and Bi1.8Pb0.4Sr2Ca2 Cu3O10+delta (2223) was studied by means of thermogravimetry, dilatometry, high-temperature resistivity, and the powder X-ray methods in the temperature range 700-1000 degrees and at P-O2 = 1-10(-4.3) atm. The existence of a high-temperature (peritectic melting) boundary of phase stability was found. The temperatures of low-temperature phase decomposition mere determined in air and under an oxygen atmosphere. The change in oxygen content was determined for the 2212 phase in the temperature range 700-860 degrees C and at P-O2 = 0.21-10(-3.7) atm by iodometric analysis of quenched samples. It was found that in the single-phase region, the change in oxygen nonstoichiometry had an insignificant influence on T-c. It was also shown that the slow cooling of samples led to a significant decrease in T-c and transport j(c) due to partial phase decomposition. (C) 1995 Academic Press, Inc.