Charge-compensated compound defects in Ga-containing thermoelectric skutterudites

Yuting Qiu, Lili Xi, Xun Shi*, Pengfei Qiu, Wenqing Zhang, Lidong Chen, James R. Salvador, Jung Y. Cho, Jihui Yang, Yuan Chun Chien, Sinn Wen Chen, Yinglu Tang, G. Jeffrey Snyder

*Corresponding author for this work

Research output: Contribution to journalArticle

83 Scopus citations

Abstract

Heavy doping changes an intrinsic semiconductor into a metallic conductor by the introduction of impurity states. However, Ga impurities in thermoelectric skutterudite CoSb3 with lattice voids provides an example to the contrary. Because of dual-site occupancy of the single Ga impurity charge-compensated compound defects are formed. By combining first-principle calculations and experiments, we show that Ga atoms occupy both the void and Sb sites in CoSb3 and couple with each other. The donated electrons from the void-filling Ga (GaVF) saturate the dangling bonds from the Sb-substitutional Ga (GaSb). The stabilization of Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga0.15Co4Sb11.95 whereas the solid-solution region in other directions of the ternary phase diagram is much smaller. A proposed ternary phase diagram for Ga-Co-Sb is given. This compensated defect complex leads to a nearly intrinsic semiconductor with heavy Ga doping in CoSb3 and a much reduced lattice thermal conductivity (κL) which can also be attributed to the effective scattering of both the low- and high-frequency lattice phonons by the dual-site occupant Ga impurities. Such a system maintains a low carrier concentration and therefore high thermopower, and the thermoelectric figure of merit quickly increases to 0.7 at a Ga doping content as low as 0.1 per Co4Sb12 and low carrier concentrations on the order of 1019 cm-3. Ga occupies both the void and Sb sites in CoSb3 which is proven by combining first-principles calculations and experiments. The stabilization of the Ga impurity as a compound defect extends the region of skutterudite phase stability toward Ga0.15Co4Sb11.95, whereas the solid-solution region becomes much smaller in other directions of the phase diagram. This compensated defect complex leads to a nearly intrinsic semiconductor with low carrier concentration, and therefore high thermopower, which possesses a much reduced lattice thermal conductivity.

Original languageEnglish (US)
Pages (from-to)3194-3203
Number of pages10
JournalAdvanced Functional Materials
Volume23
Issue number25
DOIs
StatePublished - Jul 5 2013

Keywords

  • doping
  • electrical and thermal transports
  • semiconductors
  • thermoelectrics

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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