In situobservation of the formation of FeSe

Abstract

The formation of the FeSe compound from a mixture of Fe and Se powders encased in a composite Cu/Nb sheath was studied in situ by means of high-energy synchrotron x-ray diffraction. Tetragonal β-FeSe does not seem to form directly from the starting elements. Instead, a sequence of FeSe2, Fe3Se4 and Fe7Se8 phases formed prior to the main formation stage of β-FeSe at 350–370 °C, although a small amount of this phase appears at 250 °C already during a heating ramp of 2 °C min − 1. β-FeSe transforms to δ-FeSe around 480 °C and back to β-FeSe at 405 °C during cooling. There is no evidence for any interface reaction between the metal sheath and the superconducting core.

Synthesis and Crystal Growth of Tetragonal β‐Fe1.00Se

“…In agreement with the findings from the DSC experiments, X‐ray diffraction data indicate that β‐Fe 1.00 Se remains stable up to 714 K upon heating (Figure 4). The decomposition of β‐Fe 1.00 Se into Fe‐deficient δ‐Fe 1– y Se and traces of α‐Fe in full accordance with earlier reports 6,26,27…”

Synthesis of high-quality FeSe0.5Te0.5 polycrystal using an easy one-step technique

“…Hence, the full shield is also obtained for sample S 1 though a 10-20 days annealing was abandoned, which also manifests its high quality. Compared with the reported results here and in many published papers, the quality for our sample S 1 is really improved to be a high level, in detail, the highest T c $ 14.1 K, the sharpest DT c $ 1.6 K [18][19][20][21]. A sharp decrease of resistivity below T c under a zero field is also shown in the inset in Fig.…”

“…1, it is confirmed by our results that the amount of impurity become less after annealing for sample S 3 . Nevertheless, sample S 1 fabricated using furnace cooling just shows a small amount of the Fe 7 Se 8 impurity, which is accordance with the result that the amount of Fe 7 Se 8 would become less with decrease temperature to room temperature when synthesize FeSe [21]. Therefore, there is no need to take the long term annealing process for sample S 1 .…”

Fabrication of FeSe 0 . 5 Te 0 . 5 Superconducting Wires by an Ex Situ Powder-in-Tube Method

“…Firstly, in this enlarged view, sample S 2 also shows a reaction layer. However, no interface reaction between the core and the Nb sheath is found for sample S 1 (not shown), which is in accordance with the report that no reaction layer was observed for Nb/FeSe and Nb/FeTe interfaces after the heat treatment at 584°C for 1 h [36,37]. Secondly, it should be pointed out that the brightness of the BSE image should somewhat reflect the distribution of elements.…”