SPECIFIC-HEAT OF THE 90-K SUPERCONDUCTOR TL2BA2CUO6 (2201) PREPARED IN HIGH-PRESSURE AR OR HE GAS

We present high resolution heat capacity data in the temperature range 30-300 K for several homogeneous samples of the superconductor Tl2Ba2 CuO6 (''2201'') with transition temperatures in the vicinity of 90 K. The specific heat peaks that appear close to the superconducting trans ition in some samples are identified as being due to gases trapped in the pores of the ceramics. The very small intrinsic anomaly at T(c), o f the order of 1% of the total specific heat, is best observed in samp les prepared under He atmosphere. The data are analysed using a model that includes a parametrized phonon spectrum, a mean-field jump at T(c ), and a fluctuation contribution of the Lawrence-Doniach type. The fi t yields an average coherence length of 7.5 angstrom (sample with T(c) =92 K) and 8.2 angstrom (sample with T(c)=87 K), and a vanishingly sma ll mean-field jump. The homogeneity of the electronic subsystem is que stioned. The data are compared with new results for Bi2Sr2CaCu2O8 (''2 212'', T(c)=93 K) and YBa2Cu3O7 (''123'', T(c)=91 K). The fluctuation component is similar for all three, but YBa2Cu3O7 stands out with its relatively large mean-field jump.