Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers

In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination, magnetic susceptibility, electrical resistivity, and specific heat are reported. The observation of bulk superconductivity in all thermodynamic properties -- despite strong disorder in the Fe-As layer -- favors an itinerant picture in contrast to the cuprates and renders a p- or d-wave scenario unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3) leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of states.Comment: 5 pages, 3 figure

The layered gallium borophosphate Ga[B2P2O7(OH)(5)] refined from X-ray powder data

The crystal structure of Ga[B2P2O7(OH)(5)], obtained by mild hydrothermal synthesis, has been refined from X-ray powder diffraction data using the Rietveld method. It is isotypic with the iron borophosphate Fe[B2P2O7(OH)(5)] and has a two-dimensional layered structure