Enhanced electronic and thermoelectric properties of p-type doped filled skutterudites RFe_4Sb_(12) [R=Pr, Nd)

摘要

A semimetallic type of electronic profile has been predicted for RFe_4Sb_(12) (R = Pr, Nd) from a first-principles investigation, where the presence of a small energy bandgap above the Fermi energy level (E_F) is a key feature. The E_F lies at the top of the valence band and it is crossed by a single band more than twice, which improves the band concentration and electronic specific heat as reflected by the high Seebeck coefficient. The doping of a heavy lanthanide atom at the center of the cage formed by pnictogen atoms has a significant effect on the electronic structure that enhances the Seebeck coefficient and the thermoelectric power factor. The heavy atom at the center also dampens the lattice vibration and lowers the lattice thermal conductivity. The Nd-doped system shows an enhanced Seebeck coefficient with the highest power factor among the sample alloys. Moreover, due to significant reduction in the lattice thermal conductivity from 2.46 W/mK to 0.54 W/mK, a maximum ZT value of ～1.11 at 800 K has been observed for an Nd-doped system. The covalent nature of PrFe_4Sb_(12), Pr-doped NdFe_4Sb_(12), and Nd-doped PrFe_4Sb_(12) and the ionic nature of NdFe_4Sb_(12) have been confirmed, where Pr-doped NdFe_4Sb_(12) is the stiffest and a highly rigid material with strong bonding forces among the constituent atoms. The results presented in this manuscript open the possibilities for further exploration of center atom-doped filled skutterudites with improved Seebeck coefficient and reduced lattice thermal conductivity, which are promising materials for thermoelectric applications.