Phase stability, oxygen nonstoichiometry, and superconductivity properties of Bi2Sr2CaCu2O8+δ and Bi1.8Pb0.4Sr2Ca2Cu3O10+δ

Phase stability of Bi2Sr2CaCu2O8+δ (2212) and Bi1.8Pb0.4Sr2Ca2Cu3O10+δ (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 PO2 = 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 were 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 PO2 = 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 Tc. It was also shown that the slow cooling of samples led to a significant decrease in Tc and transport jc due to partial phase decomposition