Various Arsenic Network Structures in 112-Type Ca1-xLaxFe1-yPdyAs2 Revealed by Synchrotron X-ray Diffraction Experiments.

Two novel 112-type palladium-doped iron arsenides were synthesized and identified using comprehensive studies involving synchrotron X-ray diffraction and X-ray absorption near-edge structure (XANES) experiments. Whereas in-plane arsenic zigzag chains were found in the 112-type superconducting iron arsenide Ca1-xLaxFeAs2 with maximum Tc = 34 K, deformed arsenic network structures appeared in other 112-type materials, such as longitudinal arsenic zigzag chains in CaFe1-yPdyAs2 (y ∼ 0.51) and arsenic square sheets constructed via hypervalent bonding in Ca1-xLaxFe1-yPdyAs2 (x ∼ 0.31, y ∼ 0.30). As K-edge XANES spectra clarified the similar oxidization states around FeAs4 tetrahedrons, alluding to possible parents for high-Tc 112-type iron arsenide superconductors.