Superconductivity and crystal structure of the palladium–iron–arsenides Ca₁₀(Fe_1−xPd_xAs)₁₀Pd₃As₈

Abstract

The palladium–iron–arsenides Ca₁₀(Fe_{1− x} Pd _x As)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 ) is isotypic to the homologue platinum 1038-type superconductors with alternating FeAs_4/4- and Pd₃As₈-layers, each separated by layers of calcium atoms. Iron is tetrahedrally and palladium is planar coordinated by four arsenic atoms. As₂-dimers (d _As–As ≈ 250 pm) are present in the Pd₃As₈-layer. Even though each layer itself has a four-fold 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.

Keywords:

• superconductivity
• iron-arsenides
• palladium
• crystal structure
• electronic structure

Acknowledgements

This work was financially supported by the German Research Foundation (DFG) within the priority programme SPP1458 under grant JO257/6-2. FN was supported by FP7 European project SUPER-IRON (grant agreement No.283204).