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Superconductivity and Crystal Structure of the Palladium-Iron-Arsenides Ca10(Fe1-xPdxAs)10Pd3As8

The palladium-iron-arsenides Ca10(Fe1-xPdxAs)10(Pd3As8) were synthesized by solid state methods and characterized by X-ray powder and single crystal diffraction. The triclinic crystal structure (space group P-1) is isotypic to the homologue platinum 1038 type superconductors with alternating FeAs4/4- and Pd3As8-layers, each separated by layers of calcium atoms. Iron is tetrahedral and palladium is planar coordinated by four arsenic atoms. As2-dimers (dAs-As = 250 pm) are present in the Pd3As8-layer. Even though each layer itself has a fourfold rotational symmetry, the shifted layer stacking causes the triclinic space group. Resistivity measurements of La-doped samples show the onset of superconductivity at 17 K and zero resistivity below 10 K. The magnetic shielding fraction is about 20 % at 3.5 K. 57Fe-Mössbauer spectra exhibit one absorption line and show no hint to magnetic ordering. The electronic structure is very similar to the known iron-arsenides with cylinder-like Fermi surfaces and partial nesting between hole- and electron-like sheets. Our results show that superconductivity in the palladium-iron-compounds is present but complicated by too high substitution of iron by palladium in the active FeAs-layers. Since the electronic preconditions are satisfied, we expect higher critical temperatures in Pd1038-compounds with lower or even without Pd-doping in the FeAs-layer.