Band energy and thermoelectricity of filled skutterudites LaFe_4Sb_(12) and CeFe_4Sb_(12)

摘要

Complex density functional theory (DFT) calculations of band energy structure and density of states for two principal representatives of the filled skutterudites LaFe_4Sb_(12) and CeFe_4Sb_(12) 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, LaFe_4Sb_(12) is metallic with a band crossing two times the Fermi level with direct energy gap equal to about 0.81 eV. Whereas CeFe_4Sb_(12) 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 CeFe_4Sb_(12). 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.