Oxygen non-stoichiometry of bismuth-based Bi 2Sr 2CaCu 2O 8+ x (Bi-2212) high-temperature superconductor

Abstract

Oxygen non-stoichiometry of the high-temperature superconductor Bi 2Sr 2CaCu 2O 8+ x has been investigated by the thermogravimetric technique from 250 to 820 °C over the range of phase stability corresponding to the oxygen partial pressure range from 1 to 340 mbar. The minimum concentration ( x=0.185) is set by a decomposition reaction that starts at 820 °C and by the lowest accessible oxygen partial pressures at lower temperatures. The maximum oxygen stoichiometry, which is largely independent of temperature, is set by the maximum available oxygen pressure. The accessible range in oxygen content is small below 800 °C but it increases rapidly between 800 and 820 °C. Presenting the data in the form of the thermodynamic response function makes it clear that there is no oxygen ordering in the Bi–O layers, in contrast to the Cu–O layers in YBCO.