Iron arsenides with three-dimensional FeAs layer networks: Ca(n(n+1)/2)(Fe(1−x)Pt(x))((2+3n))Pt(n(n−1)/2)As((n+1)(n+2)/2) (n = 2, 3)

We report the comprehensive studies between synchrotron X-ray diffraction, electrical resistivity and magnetic susceptibility experiments for the iron arsenides Ca(n(n+1)/2)(Fe(1−x)Pt(x))((2+3n))Pt(n(n−1)/2)As((n+1)(n+2)/2) for n = 2 and 3. Both structures crystallize in the monoclinic space group P2(1)/m (#11) with three-dimensional FeAs structures. The horizontal FeAs layers are bridged by inclined FeAs planes through edge-sharing FeAs5 square pyramids, resulting in triangular tunneling structures rather than the simple layered structures found in conventional iron arsenides. n = 3 system shows a sign of superconductivity with a small volume fraction. Our first-principles calculations of these systems clearly indicate that the Fermi surfaces originate from strong Fe-3d characters and the three-dimensional nature of the electric structures for both systems, thus offering the playgrounds to study the effects of dimensionality on high T(c) superconductivity.