HOMOGENEITY AND CRITICAL-CURRENT DENSITY OF SN-DOPED PBMO6S8 SUPERCONDUCTORS

With the overall critical current density, J(c), remaining low for PbM o6S8, the addition of 0.3 at. % Sn noticeably improved the performance . The enhancement occurs despite the presence of excess Pb and a sligh tly suppressed T-c. The increase in J(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. Detai led calorimetric investigation of undoped PbMo6S8 showed a T-c distrib ution down to 9 K evidenced by a smearing of T-c. This may be due to a progressive degradation of the sample quality leading to a plausible off-stoichiometry. High-resolution Auger electron spectroscopic experi ments suggest a variation in composition indicating excellent correspo ndence with the specific heat data. However, no such deviation was det ected for the Sn-doped samples and therefore the observed raise in J(c ). The results are discussed in conjunction with oxygen, lead and tin incorporated PbMo6S8.