Cobalt-substitution-induced Superconductivity in a New Compound with ZrCuSiAs-type Structure, SrFeAsF

摘要

We have synthesized a quaternary fluoroarsenide SrFeAsF with theZrCuSiAs-type structure (P4/nmm, a = 0.3999 and c = 0.8973 nm), which iscomposed of an alternately stacked (FeAs)- and (SrF)+ layers, analogous to theFeAs-based superconductor LaFeAsO. SrFeAsF shows metallic type conduction withthe anomaly at ~180 K. The partial replacement of the Fe with Co suppresses theanomaly and induces the superconductivity, while the maximal Tc (4 K forSrFe0.875Co0.125AsF) is much lower than that of the Co-substituted LaFeAsO.Replacement of (LaO)+ layers with (SrF)+ layers results in a enlargement of thec-axis length (+2.6%). These results suggest the importance of interlayerinteraction as a critical Tc-controlling factor in FeAs-based superconductors.