Cometal Addition Effect on Superconducting Properties and Granular Behaviours of Polycrystalline FeSe 0.5 Te 0.5 .

The enhanced performance of superconducting FeSe 0.5 Te 0.5 materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe 0.5 Te 0.5 (FeSe 0.5 Te 0.5 + x Pb + y Sn; x = y = 0-0.1) bulks are fabricated by the solid-state reaction method and characterized through various measurements. A very small amount of Sn and Pb additions ( x = y ≤ 0.02) enhance the transition temperature ( T c onset ) of pure FeSe 0.5 Te 0.5 by ~1 K, sharpening the superconducting transition and improving the metallic nature in the normal state, whereas larger metal additions ( x = y ≥ 0.03) reduce T c onset by broadening the superconducting transition. Microstructural analysis and transport studies suggest that at x = y > 0.02, Pb and Sn additions enhance the impurity phases, reduce the coupling between grains, and suppress the superconducting percolation, leading to a broad transition. FeSe 0.5 Te 0.5 samples with 2 wt% of cometal additions show the best performance with their critical current density, J c , and the pinning force, F p , which might be attributable to providing effective flux pinning centres. Our study shows that the inclusion of a relatively small amount of Pb and Sn ( x = y ≤ 0.02) works effectively for the enhancement of superconducting properties with an improvement of intergrain connections as well as better phase uniformity.