Enhancement of Seebeck coefficient for SrO(SrTiO3)2 by Sm substitution: Crystal symmetry restoration of distorted TiO6 octahedra

We found that Sm3+ substitution in SrO(SrTiO3)2 is effective in improving the Seebeck coefficient (S). The ∣S∣ value increases notably with temperature, benefiting from an enhancement of the density of states (DOS) effective mass md* from ∼3m0 (300K)to∼7.5m0 (1000K), due to an improvement of the local symmetry of TiO6 octahedra, enhancing the degeneracy in the Ti 3d orbitals, which form the conduction band (CB), and also to an accompanying lattice expansion, which gives rise to a higher DOS at the bottom of the CB and, consequently, a larger md*.