Effective mass and thermoelectric properties of SrTiO3-based natural superlattices evaluated by ab-initio calculations

The Ruddlesden-Popper phase (SrTiO₃)_n(SrO)_m with n=2, m=1 is considered as an advanced thermoelectric layered material based on ceramic semiconductors and combines the high electric conductivity of SrTiO₃ with the low thermal conductivity of SrO due to the concept of nanoblock integration. However, it still need to be improved: in SrTiO₃ the effective mass as one of main factors for the Seebeck coefficient can be enlarged through substitution by heavy elements as calculated from the curvature of the electronic band structure. The effective mass increases with the substitution of Ba on the A-site and V on the B-site in SrTiO₃. For the RP-phases STO327, STO214 it shows anisotropy of more than a factor of two for in-plane and out-of-plane-directions and the Sr-O and Ti-O bonds show a stronger localization at the SrO/SrTiO₃ interface than in SrTiO₃-bulk, but the average effective mass is rather low.