Abstract
A semimetallic type of electronic profile has been predicted for RFe4Sb12 (R = Pr, Nd) from a first-principles investigation, where the presence of a small energy bandgap above the Fermi energy level (EF) is a key feature. The EF 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/m K to 0.54 W/m K, a maximum ZT value of ∼1.11 at 800 K has been observed for an Nd-doped system. The covalent nature of PrFe4Sb12, Pr-doped NdFe4Sb12, and Nd-doped PrFe4Sb12 and the ionic nature of NdFe4Sb12 have been confirmed, where Pr-doped NdFe4Sb12 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