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

Abstract

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)^δ− and (SrF)^δ+ layers, analogous to the FeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction with the anomaly at ∼180 K. The partial replacement of the Fe with Co suppresses the anomaly and induces the superconductivity, while the maximal T_c (4 K for SrFe_0.875Co_0.125AsF) is much lower than that of the Co-substituted LaFeAsO. Replacement of (LaO)^δ+ layers with (SrF)^δ+ 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.