Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles

Eric B. Isaacs, Christopher Wolverton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Filling the large voids in the crystal structure of the skutterudite CoSb3 with rattler atoms R provides an avenue for both increasing carrier concentration and disrupting lattice heat transport, leading to impressive thermoelectric performance. While the influence of R on the lattice dynamics of skutterudite materials has been well-studied, the phase stability of R-filled skutterudite materials and the influence of the presence and ordering of R on the electronic structure remain unclear. Here, focusing on the Yb-filled skutterudite YbxCo4Sb12, we employ first-principles methods to compute the phase stability and electronic structure. Yb-filled CoSb3 exhibits (1) a mild tendency for phase separation into Yb-rich and Yb-poor regions and (2) a strong tendency for chemical decomposition into Co-Sb and Yb-Sb binaries (i.e., CoSb3, CoSb2, and YbSb2). We find that, at reasonable synthesis temperatures, configurational entropy stabilizes single-phase solid solutions with limited Yb solubility, in agreement with experiments. Filling CoSb3 with Yb increases the band gap, enhances the carrier effective masses, and generates new low-energy "emergent" conduction band minima, which is distinct from the traditional band convergence picture of aligning the energies of existing band extrema. The explicit presence of R is necessary to achieve the emergent conduction band minima, though the rattler ordering does not strongly influence the electronic structure. The emergent conduction bands are spatially localized in the Yb-rich regions, unlike the delocalized electronic states at the Brillouin zone center that form the unfilled skutterudite band edges.

Original languageEnglish (US)
Pages (from-to)6154-6162
Number of pages9
JournalChemistry of Materials
Volume31
Issue number16
DOIs
StatePublished - Aug 27 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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