The family of iron arsenide superconductors is expanded by the new iron platinum compounds (CaFe1−xPtxAs10)Pt4−yAs8 with novel crystal structures. Layers of FeAs4/4 tetrahedra and of nearly planar PtAs4/2 squares with (As2)4− dumbbells are stacked in different ways, resulting in polytypes with triclinic or tetragonal symmetry. Superconductivity up to 35 K is induced either by Pt doping of the Fe site or by electron transfer from PtAs to FeAs layers.

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The new calcium iron arsenide compounds Ca(n(n+1)/2)(Fe(1-x)M(x))(2+3n)M'(n(n-1)/2)As((n+1)(n+2)/2) (n = 1-3; M = Nb, Pd, Pt; M' = □, Pd, Pt) were synthesized and their crystal structures determined by single-crystal X-ray diffraction. The series demonstrates the structural flexibility of iron arsenide materials, which otherwise prefer layered structures, as is known from the family of iron-based superconductors. In the new compounds, iron arsenide tetrahedral layers are bridged by iron-centered pyramids, giving rise to so far unknown frameworks of interconnected FeAs layers. Channels within the structures are occupied with calcium and palladium or platinum, respectively. Common basic building blocks are identified that lead to a better understanding of the building principles of these structures and their relation to CaFe4As3.

SrPt 2 As 2 undergoes a structural transition around 470 K (from a high-temperature tetragonal to a lowtemperature orthorhombic phase) accompanied by a charge density wave transition and followed by a superconducting transition at much lower temperature (5 K). The superconducting gap symmetry of this noncentrosymmetric compound was investigated in detail by means of muon-spin rotation or relaxation (μSR) experiments in transverse-field (TF) configuration. The temperature-dependent magnetic penetration depth obtained from the TF-μSR spectra suggests an isotropic s-wave-type superconducting gap. No observable differences are seen in the asymmetry time spectra collected in zero field above and below the superconducting transition temperature T c. This strongly suggests the absence of spontaneous magnetic fields in the superconducting state, hence pointing to a preserved time-reversal symmetry below T c .