Issue
EPL
Volume 86, Number 3, May 2009
Article Number 37008
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/86/37008
Published online 22 May 2009
EPL, 86 (2009) 37008
DOI: 10.1209/0295-5075/86/37008

Preparation and superconductivity of stoichiometric $\beta$-FeSe

Yujuan 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

huangfq@mail.sic.ac.cn

received 20 January 2009; accepted in final form 6 April 2009; published May 2009
published online 22 May 2009

Abstract
The stoichiometric $\beta$-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 $\beta$-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 $\gamma $-Fe7Se8, tetragonal $\beta$-FeSe, and residual Fe coexist when t $\leqslant$ 5 h. A single $\delta $-FeSe phase is observed when t = 10 h, and the crystalline size further decreases to ~ 10 nm. In the nanocrystalline state, hexagonal $\delta $-FeSe is the stable and preferred phase. With the increase of the annealing temperature, $\delta $-FeSe rapidly transforms to the well-crystallized $\beta$-FeSe. At 400 °C, the pure stoichiometric $\beta$-FeSe phase is successfully obtained with size of ~ 60 nm and the highest superconductor transition temperature Tconset of about 8.9 K in the $\beta$-FeSe1-x series.

PACS
74.70.-b - Superconducting materials.
74.70.Ad - Metals; alloys and binary compounds (including A15, MgB2, etc.).

© EPLA 2009