SPECIFIC-HEAT OF BI2SR2CACU2OX VERSUS OXYGEN-CONTENT LESS-THAN-OR-EQUAL-TO-B-LESS-THAN-OR-EQUAL-TO-14T)

In order to characterize more precisely the superconducting transition of a quasi-2D superconductor, we quenched polycrystalline samples of Bi2Sr2CaCu2Ox from various locations of the (T; p(O2)) equilibrium dia gram. A well-defined specific heat peak at T(c) is observed with 0.01% resolution for the samples with the highest T(c). The samples with lo wer T(c)'s provide strong support to the normal-state background deter mined by an analysis of the data including phonon and fluctuation term s. We do not find any indication of a mean-field jump within experimen tal uncertainty, in stark contrast to YBa2Cu3O7. The application of a 14 Tesla field depresses the total specific heat by 0.54% only at T(pe ak)=92.5K, but this effect reduces to less than 0.03% already +/-8K aw ay from T(c). On passing the irreversibility line, no anomaly in the s pecific heat is detected at the 0.01% level.