THE SPECIFIC-HEAT ANOMALY OF BI2SR2CACU2O8-CONTENT(DELTA AT T(C) IN DEPENDENCE ON THE OXYGEN)

Melt casting processed samples of Bi2Sr2CaCu2O8+delta were prepared wi th oxygen contents ranging from delta=0.126 to delta=0.22 and characte rized by electrical resistance and AC-susceptibility. The T(c) of this compound is shifted reversibly between 75 and 95 K by annealing in Ar and/or O2 atmospheres for various times. The anomalies of the specifi c heat at T(c) were measured with a resolution of DELTAC/C almost-equa l-to 5 x 10(-4). They can be described by a superposition of a mean fi eld step and a contribution due to strong, two-dimensional fluctuation s. By a fit of a model with 2D gaussian fluctuations to the specific h eat near T(c) we estimate DELTAC and the in-plane coherence length xi( parallel-to) (0) of the superconductor.