Abstract
The resistance, ac susceptibility and Hall coefficient measurements were carried out for the high quality single phase Bi2Sr2CaCu2Oy samples with different oxygen contents. It is found that the number of extra oxygen atoms in the samples can be easily modulated when they are annealed in low vacuum, and that the relationship between Tc and P+ is unmonotonic with an optimum P+=0.27 holes/CuO2 plane corresponding to the highest Tc (=95 K). This unmonotonic relationship is discussed briefly.