Specific heat study of the Na0.3CoO2•1.3H2O superconductor:: influence of the complex chemistry

We report results of specific heat measurements on polycrystalline samples of the layered superconductor, Na0.3CoO2 . 1.3H(2)O. The electronic contribution to the specific heat, gamma, is found to be 12.2 mJ/mol K-2. The feature at the superconducting transition is rather sharp, becoming broad and strongly suppressed in an applied magnetic field. The data indicate a residual normal state electronic specific heat at low temperatures, implying that there is a sizable population of normal state electrons in the samples even below T-c. Inhomogeneity in the Na content, to which the superconducting state is exquisitely sensitive, appears to be the most likely explanation for these results. These results further indicate that special sample handling is required for an accurate characterization of the superconducting state in this material. (C) 2003 Elsevier B.V. All rights reserved.