Synthesis, thermal stability, structural features, and electromagnetic properties of Bi2+xSr2-xCuO6+delta (0 <= x <= 0.4)

The thermal stability and structural modulation were studied systematically in a wide range of 0 less than or equal to x less than or equal to 0.4 for the 2201 phase in the Bi-Sr-Cu-O system, Bi2 + x Sr2-xCUO6 + 8, and it was found that these properties varied remarkably at x approximate to 0.1. Com positions 0 less than or equal to x < 0.1 remained stable only in a narrow low-T high-P-O2 region and their modulation period changed stepwisely, not continuously, and reversibly between 4.9b (oxidized) and 5.5b (reduced) whe n the oxygen content was changed only by 0.65%. In relation to this we prop ose for 0 less than or equal to x < 0.1 specifically that the change in oxy gen content induces the exchange of small amounts of Bi and Sr ions between the 'BiO' and 'SrO' sheets. The superconductivity of the cation-stoichiome tric composition (x = 0) was also studied as a function of oxygen content. (C) 1999 Elsevier Science B.V. All rights reserved.