Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 18: Superconductivity: Fabrication and Characterization

TT 18.2: Talk

Tuesday, March 24, 2009, 14:15–14:30, HSZ 105

Preparation and Analysis of the new Superconductors RO_1−xF_xFeAs (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 RO_1−xF_xFeAs (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 RO_1−xF_xFeAs phase mainly, only small amount of RO_yF_z and FeAs are found. We find that the measured fluorine content can deviate from the initial weight. In the lanthanum compound LaO_1−xF_xFeAs, 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 LaO_1−xF_xFeAs and SmO_1−xF_xFeAs. Furthermore, we studied which preparation steps are crucial for the fluorine incorporation.