Wide-range oxygen doping of Bi2Sr2CaCu2O8+δ

The high-temperature superconductor Bi2Sr2CaCu2O8+δ has been doped with oxygen at pressures ranging from a few μbar to 4 kbar. The doping is reversible by heat treatment in air at ambient pressure. Electrical-resistivity and infrared-optical-transmission measurements indicate that the carrier density increases monotonically with the oxygen annealing pressure. The superconductor transition goes through a maximum near 90 K and can be reduced by at least 30 K on both sides of the doping curve. In the oxygen-rich material the resistivity in the a-b plane exhibits a superlinear T1+x behavior while the c-axis resistivity shows a positive slope in the temperature dependence.