Dresden 2009 – wissenschaftliches Programm
TT 18.2: Vortrag
Dienstag, 24. März 2009, 14:15–14:30, HSZ 105
Preparation and Analysis of the new Superconductors RO1−xFxFeAs (R = La, Ce, Nd, Sm, Gd) — •Anke Köhler, Günter Behr, Jochen Werner, Daniel Koksch, Rüdiger Klingeler, Norman Leps, Jorge E. Hamann-Borrero, and Bernd Büchner — IFW Dresden, PF 270116, D-01171 Dresden
Polycrystalline samples of RO1−xFxFeAs (0≤x≤0.25) were prepared in a two step method, similar described by Zhu et al. . In the first step FeAs is prepared which is milled afterwards. In the second step the FeAs powder is mixed together with rare-earth-oxides, -flourides and -pure element powders and pressed into pellets under a well defined pressure. Then, the samples were heated in an evacuated silica tube at 940∘C and 1150∘C. The composition of the samples and particularly the fluorine content was determined by wavelength-dispersive X-ray spectroscopy (WDX) in the electron microscope. The polycrystalline samples consist of the RO1−xFxFeAs phase mainly, only small amount of ROyFz and FeAs are found. We find that the measured fluorine content can deviate from the initial weight. In the lanthanum compound LaO1−xFxFeAs, e.g., we found a good agreement mainly for x>0.05, but the fluorine hardly goes into the sample for x<0.05. For the samarium compound again we measure less fluorine in the sample as weighted for all fluorine contents. These measured values are taken into account when drawing the electronic phase diagrams of LaO1−xFxFeAs and SmO1−xFxFeAs. Furthermore, we studied which preparation steps are crucial for the fluorine incorporation.