Influence of Premilling Time on the Sintering Process and Superconductive Properties of FeSe

A facile combinative method with mechanical alloying and solid-state reaction was adopted to produce tetragonal β-FeSe using Fe and Se powders. The powder mixtures were premilled for different times and then sintered at 750
^°
C with a one-step method. The effect of synthesis parameters, microstructures, sintering process, and superconducting properties on FeSe bulks was well investigated. It indicated that mechanical alloying played an important role in the sintering process and morphologies of the FeSe bulk samples. The sintering process for the 50-h premilled sample changed a lot. From the differential thermal analysis measurements, the band of iron selenides splits into two peaks, of which the former exceeds the peak for Se fusion. In addition, the premilled sample for 20 h exhibited fine grains, whereas the 50-h sample exhibited fine stratified crystals. Meanwhile, the lattice parameters and the volume fraction of β-FeSe increased with the milling time. However, the slight fluctuation in lattice parameters and volume fraction led to slight variation in transition temperature
Tc
.