Influences of Fe content on the fabrication of FeSe superconductors with high-energy ball milling aided sintering process.

Fe x Se superconducting bulks with different norminal Fe content from x = 1.00 to 1.20 have been fabricated with high-energy ball milling (HEBM) aided sintering process. The influences of original Fe contents on the phase composition, microstructures and superconducting properties were systematically investigated. It was noticed that with the increase of original Fe content, the nonsuperconducting δ-FeSe phase content decreased, while the content of residual Fe increased correspondingly. Meanwhile, the increasing original Fe content could also cause the increase of FeSe crystal size, therefore, the (00 l ) texture of FeSe bulks was enhanced, which would be beneficial to the intergrain connections. Mössbauer spectra have been performed to study the magnetic orders in obtained FeSe bulks. A clear hyperfine magnetic sextet corresponding to the magnetic ordering with H f of 333.0 kOe can be related to residual Fe in the bulks with Fe content higher than 1.10. The magnetic and superconducting properties of obtained bulks underwent a systematical change with original Fe content. The increasing Fe content can obviously enhance the superconducting performance of FeSe bulks and the optimal critical temperature, T c of 9.0 K was obtained with original Fe content of 1.20. [ABSTRACT FROM AUTHOR]