Homogeneity and critical current density of Sn-doped PbMo6S8 superconductors

With the overall critical current density,J _c , remaining low for PbMo₆S₈, the addition of 0.3 at. % Sn noticcably improved the performance. The enhancement occurs despite the presence of excess Pb and a slightly suppressedT _c . The increase inJ _c can be attributed to a better homogeneity with respect to the chemical composition of the samples, which may be as a consequence of Sn substitution in the lattice. Detailed calorimetric investigation of undoped PbMo₆S₈ showed aT _c distribution down to 9 K evidenced by a smearing ofT _c . This may be due to a progressive degradation of the sample quality leading to a plausible off-stoichiometry. High-resolution Auger electron spectroscopic experiments suggest a variation in composition indicating excellent correspondence with the specific heat data. However, no such deviation was detected for the Sn-doped samples and therefore the observed raise inJ _c . The results are discussed in conjunction with oxygen, lead and tin incorporated PbMo₆S₈.