Structure and physical properties of the new layered oxypnictides Sr4Sc2O6M2As2 (M=Fe and Co)

We have successfully prepared the new layered oxypnictides Sr4Sc2O6M2As2 (M=Fe and Co). They adopt the tetragonal structure, being the same as that of Sr4Sc2O6Fe2P2. The lattice constants are a=0.4045 nm and c=1.5802 nm for M=Fe, and a=0.4045 nm and c=1.5695 nm for M=Co, respectively. Their transport and magnetic properties have been systematically studied. The temperature dependence of the Hall coefficient and the thermoelectric power for the Sr4Sc2O6Fe2As2 compound show a complicated behavior, similar to that of the iron-based parent compounds LnOFeAs and BaFe2As2. This suggests that Sr4Sc2O6Fe2As2 could be considered as a new parent compound of iron-based superconductors.