Cobalt-Substitution-Induced Superconductivity in a New Compound with ZrCuSiAs-Type Structure, SrFeAsF

We have synthesized a quaternary fluoroarsenide SrFeAsF with the ZrCuSiAs-type structure (P4/nmm, a = 0.3999 and c = 0.8973 nm), which is composed of an alternately stacked (FeAs)(delta-) and (SrF)(delta+) layers, analogous to the FeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction with the anomaly at similar to 180 K. The partial replacement of the Fe with Co suppresses the anomaly and induces the superconductivity, while the maximal T-c (4K for SrFe0.875Co0.125AsF) is much lower than that of the Co-substituted LaFeAsO. Replacement of (LaO)(delta+) layers with (SrF)(delta+) layers results in a enlargement of the c-axis length (+2.6%). These results suggest the importance of interlayer interaction as a critical T-c-controlling factor in FeAs-based superconductors.