Oxygen-loss effects on superconductivity of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{y}}$ system

The properties of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{y}}$ annealed at 200–650 °C in vacuum (${10}^{\mathrm{-}4}$Pa) are studied by x-ray powder diffraction, ac magnetization, and Hall measurement. The amount of oxygen loss, Δy, was obtained by an integration of the oxygen partial pressure measured by a quadrupole mass spectrometer. The ${\mathit{T}}_{\mathit{c}}$ increases from 65 to 92 K, which is accompanied by a small amount of oxygen loss (on the order of ${10}^{\mathrm{-}3}$). 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 ${\mathit{T}}_{\mathit{c}}$, 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.