Abstract
We have mapped the critical temperature of Bi 2Sr 2CaCU 2O 8+δ (2212) in the ( p, T) plane for 10 −5 ≤ p ≤ 80 bar (O 2) and 300 ≤ T ≤ 840°C. Equilibrium conditions are frozen by quenching the samples into liquid gallium. The DC diamagnetic transitions remain sharp, and span an unusual temperature range for the 2212 phase (51.5 K to 94.4 K). This variation is attributed to a measured 2.5% change of the oxygen content ( Δδ ⋍ 0.2) in the structure. At the same time, we do not observe any significant variation of the lattice parameters. The Meissner effect, measured in an external magnetic field of 20 Oe, increases with T c. The slope of the normal-state susceptibility ∂ χ / ∂T becomes markedly less negative with decreasing oxygen concentration. It vanishes for the optimum doping that leads to T c ⋍ 94 K .
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