Sr3Sc2Fe2As2O5 as a possible parent compound for FeAs-based superconductors

A compound with the FeAs-layers, namely, (Sr3Sc2O5)Fe2As2 (abbreviated as FeAs-32522), was successfully fabricated. It has a layered structure with the space group of I4/mmm, and with the lattice constants a=4.069 A and c=26.876 A. The in-plane Fe ions construct a square lattice which is close to that of other FeAs-based superconductors, such as REFeAsO (RE=rare earth elements) and (Ba,Sr)Fe2As2. However the inter-FeAs-layer spacing in the compound is greatly enlarged. The temperature dependence of resistivity exhibits a weak upturn in the low-temperature region, but a metallic behavior was observed above about 60 K. The magnetic susceptibility shows also a nonmonotonic behavior. Interestingly, the well-known resistivity anomaly which was discovered in all other parent compounds, such as REFeAsO, (Ba,Sr)Fe2As2 and (Sr,Ca,Eu)FeAsF and associated with the spin-density wave/structural transition has not been found in the new system either on the resistivity data or the magnetization data. This could be induced by the large spacing distance between the FeAs-planes, therefore the antiferromagnetic correlation between the moments of Fe ions in neighboring FeAs layers cannot be established. Alternatively it can also be attributed to the self-doping effect between Fe and Sc ions. The Hall coefficient R-H is negative but strongly temperature dependent in wide temperature region, which indicates the dominance of electrical conduction by electronlike charge carriers and probably a multiband effect or a spin related scattering effect. It is found that the magnetoresistance cannot be described by Kohler's rule, which gives further support to above arguments.