Oxygen stoichiometry-Tccorrelations in Bi2Sr2CaCu2O8+x

Abstract
The oxygen content of single-phase Bi2Sr2CaCu2O8+x depends on the annealing temperature and the oxygen partial pressure. The Tc maximum, 87 K, is associated with an excess oxygen content, x, of 0.035+or-0.003, as determined by volumetric analysis and thermogravimetry. This stoichiometry is obtained by, for instance, annealing in air at approximately 820 degrees C or in nitrogen at approximately 400 degrees C. For higher and lower x, Tc decreases. No structural changes associated with this change in oxygen content were observed; variations in Tc appear therefore to be associated with changes in carrier concentration. The rate of change of Tc with x is more than ten times greater than in YBa2Cu3Ox.