Oxygen-loss effects on superconductivity of Bi2Sr2CaCu2Oy system

The properties of Bi2Sr2CaCu2Oy annealed at 200650°C in vacuum (10-4Pa) are studied by x-ray powder diffraction, ac magnetization, and Hall measurement. The amount of oxygen loss, y, was obtained by an integration of the oxygen partial pressure measured by a quadrupole mass spectrometer. The Tc increases from 65 to 92 K, which is accompanied by a small amount of oxygen loss (on the order of 10-3). The a and c axes are extended by the oxygen loss. The change of the hole concentration estimated by Hall measurement is of the same order of magnitude as that for the other superconducting oxides against the change of Tc, however, it is larger by about two orders of magnitude than that expected from the oxygen loss. This discrepancy suggests charge redistribution in the structure.