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Fluorine doping Fe1.2Se polycrystalline were prepared by solid-state sintering method. The influences of fluorine doping content and sintering temperatures on phase composition, lattice parameters, microstructure as well as superconducting properties were discussed in detail. It was found that fluorine doping could effectively reduce the content of non-superconducting hexagonal δ-FeSe phase. Besides, the content of hexagonal δ-FeSe phase and grain size of superconducting tetragonal β-FeSe phase were decreased with the sintering temperature increasing. Scanning electron microscopes (SEM) images indicated that the morphology of β-FeSe phase was a typical lamellar structure with the small particles of hexagonal δ-FeSe phase. Meanwhile, a higher critical temperature Tc of 8.3 K and larger shield volume fraction were obtained with high sintering temperature of 950 °C and proper F doping content. [ABSTRACT FROM AUTHOR]

Cl-doped Fe(Se, Te) superconductors were fabricated through a melting method followed by hydrostatic pressure (HP) post treatment. A dual coordination effect has been aroused, viz. the introduction of Cl− ions triggered the nucleation and growth of nanometric point-like secondary phase as extra pinning centers, while HP strengthened the pinning competence of these point defects. As a result, the superconducting phase volume, critical temperature, and critical current density have been improved by 12.2%, 42.3%, and nearly 100 times, respectively, compared with the undoped sample without HP. Unlabelled Image [ABSTRACT FROM AUTHOR]

Superconducting FeSe bulks with high superconducting content of PbO-type tetragonal β-FeSe phase were prepared with high-energy ball milling (HEBM) aided sintering process. During the HEBM process, different ball-to-powder ratios of 6:1, 8:1, and 10:1 were adopted. The influences of ball-to-powder ratio on the phase composition of both ball milled powders and sintered bulks, morphology, and superconducting properties of final bulks were systematically investigated. It was noticed that, with the increase of ball-to-powder ratio, the energy input into the ball milling system increased, and the high-energy collision times increased. Therefore, more Fe atoms entered into the Fe-Se matrix, and the ball milling products changed from Fe3Se4 to Fe7Se8. On the other hand, the decreasing total collision times led to the increase of final particle size. After the same sintering process, FeSe bulks with the major phase of β-FeSe were all obtained. However, with the increasing ball-to-powder ratio, the contents of both hexagonal δ-FeSe phase and residual Fe contents increased. Due to the different Fe/Se ratio in the final β-FeSe phase, the superconducting transition behavior varied obviously. Higher critical temperature of 8.0 K and larger superconducting phase content were achieved with the optimal ball to powder ratio of 6:1. [ABSTRACT FROM PUBLISHER]

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]