Electronic and thermoelectric properties of Nd-doped Ce-filled skutterudites

The electronic and thermoelectric properties of Nd-doped Ce-filled skutterudites (CeFe₄P₁₂, CeFe₄As₁₂, and CeOs₄P₁₂) were explored using full-potential linearized augmented plane waves (FP-LAPW). The exchange-correlation between the electrons was treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE) and the Coulomb repulsion term (U) between the electrons for the highly correlated system was also considered. The energy band structures revealed the semiconducting nature with energy gaps of 0.42 eV, 0.25 eV and 0.22 eV for CeFe₄P₁₂, CeFe₄As₁₂, and CeOs₄P₁₂, respectively. The phonon dispersion curve displayed the forbidden gap between the optical and acoustic modes in CeFe₄P₁₂ and CeOs₄P₁₂. The analysis of n-type and p-type doping on pure alloys suggest enhanced thermoelectric behavior in p-type doping on pure alloys and hence the addition of Nd at the central cage atomic site generates flat and dense bands at E_F and also opens an optical band gap in doped CeOs₄P₁₂. Moreover, the Nd atom introduces strong phonon scattering and hence reduces the lattice thermal conductivity (K_L) substantially from 6.79 W m^-1 K^-1 to 3.47 W m^-1 K^-1 for CeFe₄P₁₂, 3.63 W m^-1 K^-1 to 1.97 W m^-1 K^-1 for CeFe₄As₁₂ and 6.43 W m^-1 K^-1 to 2.58 W m^-1 K^-1 for CeOs₄P₁₂ at room temperature. A considerably amplified figure of merit has been observed for the doped sample materials with the highest value of 0.72 at 800 K for doped CeFe₄P₁₂ with the highest Seebeck coefficient of 215.51 μV K^-1.