Preparation and superconductivity of stoichiometric -FeSeYujuan Xia1, Fuqiang Huang1, Xiaomin Xie2 and Mianheng Jiang2
1 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences - Shanghai 200050, PRC
2 Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences Shanghai 200050, PRC
received 20 January 2009; accepted in final form 6 April 2009; published May 2009
published online 22 May 2009
The stoichiometric -FeSe superconductor was prepared for the first time by mechanical alloying (MA) from elemental powders of iron and selenium (1 : 1) and subsequent annealing process. The formation of the stoichiometric -FeSe is attributed to the MA resulting nanometric precursor containing high reaction activity for the following annealing process, and the MA mechanism here is a mechanic collision reaction (MCR). The crystalline phases in the MA precursor are tightly related to the milling time (t). Hexagonal -Fe7Se8, tetragonal -FeSe, and residual Fe coexist when t 5 h. A single -FeSe phase is observed when t = 10 h, and the crystalline size further decreases to ~ 10 nm. In the nanocrystalline state, hexagonal -FeSe is the stable and preferred phase. With the increase of the annealing temperature, -FeSe rapidly transforms to the well-crystallized -FeSe. At 400 °C, the pure stoichiometric -FeSe phase is successfully obtained with size of ~ 60 nm and the highest superconductor transition temperature Tconset of about 8.9 K in the -FeSe1-x series.
74.70.-b - Superconducting materials.
74.70.Ad - Metals; alloys and binary compounds (including A15, MgB2, etc.).
© EPLA 2009