Thermoelectric properties of FeAs based superconductors, with thick perovskite- and Sm-O fluorite-type blocking layers

• Thermoelectric properties are studied for 22438 and 225411 with Sm1111.
• Thermal and electrical coeff. follow almost the same behaviour for both categories.
• The thermoelectric figure of merit has low value from the application point.
• Major contribution to the normal state conductivity is by electron type carriers.

The transport properties (electrical resistivity, Hall and Seebeck coefficient, and thermal conductivity) of iron based superconductors with thick perovskite-type oxide blocking layers and fluorine-doped SmFeAsO were studied to explore their possible potential for thermoelectric applications. The thermal conductivity of former compounds depicts the dominated role of phonon and its value decreases rapidly below the Tc, suggesting the addition of scattering of phonons. Both the Seebeck coefficient (S) and Hall coefficient (RH) of all samples were negative in the whole temperature region below 300 K, indicating that the major contribution to the normal state conductivity is by electrons. In addition, the profile of S(T) and RH(T) of all samples have similar behaviours as would be expected for a multi-band superconductors. Although the estimated thermoelectric figure of merit (ZT) of these compounds was much lower than that of practically applicable thermoelectric materials, however its improvement can be expected by optimizing microstructure of the polycrystalline materials, such as densification and grain orientation.