THERMAL-EXPANSION, SPECIFIC-HEAT, AND UNIAXIAL PRESSURE DEPENDENCES OF T-C, IN BI2SR2CACU2O8+DELTA

The coefficients of the thermal expansion parallel (alpha(a,b)) and pe rpendicular (alpha(c)) to the CuO2 planes as well as the specific heat (c(p)) of a Bi(2)Sr(2)CaCu(2)0(8+delta) single crystal have been meas ured. A clear anomaly at T-c is present in alpha(a,b) whereas no corre sponding anomaly could be observed in alpha(c). The anomalies of c(p) as well as alpha(a,b) show pronounced fluctuations of the superconduct ing order parameter and in addition a small mean-field-like increase o f alpha(a,b) below T-c can be resolved, where the relative size of the anomaly is much larger than in the specific heat. Comparing the anoma lies of alpha(a,b) and c(p) an uniaxial pressure dependence for pressu re parallel to the CuO2 planes of dT(c)/dp(a,b) = 0.9(1) K/GPa is dete rmined for Bi2212, which seems to represent the ''intrinsic'' pressure dependence of the high-T-c cuprates. Besides the anomaly at T-c we ob serve a jump-like increase of the thermal expansion parallel to the c- axis at about 120 K indicating a structural instability of Bi2Sr2CaCu2 O8+delta at this temperature.