Optimization of High-Energy Ball-Milling Time for Fe_1.1Se_0.5Te_0.5 Polycrystalline Superconductors

The Fe_1.1Se_0.5Te_0.5 polycrystalline superconductors were prepared by a high-energy ball-milling (HEBM) technique. Ball-milling times of 0, 2, 4, 6, and 8 h were adopted to optimize this technique. The influences of ball-milling time on the phase distributions of milled powders and sintered bulks, the morphology of ball-milled powders, and superconducting properties of final sintered bulks were systematically studied. It was found that with increasing ball-milling time, the ball-milled powders changed from a crystal to a noncrystalline and then to an alloy. At the same time, the main phases in ball-milled powders changed from original mixed powders of Fe, Se, and Te to (Se, Te) solid solution, and then to the two phases of β-Fe(Se, Te) and δ -Fe(Se, Te), accordingly. Due to the reduction in diffusion length, it was more likely for HEBM powders to form FeSeTe ternary alloys. Thus, the obtained Fe(Se, Te) bulk with HEBM time of 4 h exhibited the highest T_c of 14.3 K and the largest content of superconducting phase. However, in the samples achieved by longer HEBM time, phase segregation and oxidation were observed. Therefore, the HEBM time of 4 h is the most suitable for the fabrication of high-quality precursor powders according to these experiments.