Band energy and thermoelectricity of filled skutterudites LaFe4Sb12 and CeFe4Sb12

Complex density functional theory (DFT) calculations of band energy structure and density of states for two principal representatives of the filled skutterudites LaFe4Sb12 and CeFe4Sb12 have been performed using the tight-binding, linear muffin-tin orbital (TB-LMTO) and full potential linear augmented plane wave (FP-LAPW) methods to clarify origin of thermoelectricity. Both methods were used within a framework of the LDA approach. We have found that both methods show similar band energy dispersion features with minor differences. Particularly, LaFe4Sb12 is metallic with a band crossing two times the Fermi level with direct energy gap equal to about 0.81 eV. Whereas CeFe4Sb12 is a semiconductor with indirect energy gap equal to about 0.66 eV. Our calculations performed for density of electronic states near the Fermi energy level show that the large thermopower at room temperature originates from the d Fe states hybridized with the p states of Sb and that there is no contribution from the Ce states in the case of CeFe4Sb12. Because these two compounds are strongly correlated fermions systems, during calculations of thermoelectric properties, this factor may play several roles. Role of spin fluctuations in the observed thermopower dependencies is also discussed.