Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Fachverband Tiefe Temperaturen

TT 20: SC: Fabrication and Characterization of Iron-Based and Other Superconductors

TT 20.7: Vortrag

Mittwoch, 24. März 2010, 11:00–11:15, H19

How Can We Raise T_c in RO_1−xF_xFeAs Superconductors? — •Anke Köhler^1,2, Günter Behr¹, Marko Herrmann¹, and Wolfgang Häßler¹ — ¹IFW Dresden, PF 270116, 01171 Dresden — ²Goethe-Universität Frankfurt am Main, Max-von-Laue-Str. 1, 60438 Frankfurt

By the discovery of RO_1−xF_xFeAs (R = lanthanide) superconductors in the beginning of 2008, it was shown for the first time that a non-cuprate superconductor can reach a superconducting transition temperature T_c above 50 K. This offers new opportunities for the development of new high temperature superconductors. However, the superconductors with the highest T_c show the most difficulties in formation of the right phase. Problems are the incorporation of fluorine and the homogeneity of the samples. A further challenge is the structural instability for rare earth elements with small ion radius (64≤Z≤71). In our studies, several opportunities to overcome these difficulties are evaluated:

1. variation of the grain size of the initial powder

2. use of slightly non-stoichiometric initial composition

3. high-pressure synthesis

As a result, we raise the T_c of the material with a nominal composition GdO_1−xF_xFeAs from 20 up to 40 K. In a SmO_0.9F_0.1FeAs-compound could be observed superconductivity above 50 K after a small As-reduction at the surface of the sample. Measurements of the final composition and structure will animate the discussion about the requirements for realization of the superconducting state.