Argyrodite-Type Cu8GeSe6–xTex (0 ≤ x ≤ 2): Temperature-Dependent Crystal Structure and Thermoelectric Properties

Stefan Schwarzmüller, Daniel Souchay, Daniel Günther, Alex Gocke, Iurii Dovgaliuk, Samuel A. Miller, G. Jeffrey Snyder, Oliver Oeckler*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Substitution of Se by Te in argyrodite-like Cu8GeSe6 leads to compounds Cu8GeSe6–xTex (0 ≤ x ≤ 2) and involves a structure change from the Cu8GeSe6 type to the Ag8GeTe6 type. The crystal structure of Cu8GeSe4.25Te1.75 between 50 °C and 500 °C reveals pronounced disorder of Cu atoms that is best described by anharmonic atomic displacement parameters using the Gram-Charlier expansion. Diffusion pathways are visualized by isosurfaces of joint probability density functions. The lattice parameter a increases with temperature in two linear regimes from 10.4682(18) Å to 10.609(3) Å with a superionic transition at 400 °C. The potential barrier for Cu is about 90 meV at 50 °C, which is in the range of typical ion conductors. Cu8GeSe4Te2 exhibits a higher thermoelectric figure of merit (zT = 0.65 at 350 °C) than Cu8GeSe6 (zT = 0.2 at 350 °C). The application of an effective mass model reveals that the charge carrier concentration of 6 × 1020 cm–3 is close to optimum. In addition, argyrodite-type precipitates form heterostructures with a Cu- and Se-doped matrix of germanium antimony tellurides in the quinary system Cu/Ge/Sb/Se/Te, whose transport properties were characterized.

Original languageEnglish (US)
Pages (from-to)1915-1922
Number of pages8
JournalZeitschrift fur Anorganische und Allgemeine Chemie
Volume644
Issue number24
DOIs
StatePublished - Dec 31 2018

Keywords

  • Argyrodite
  • PLEC
  • Single crystal
  • Synchrotron diffraction
  • Tellurium
  • Thermoelectrics

ASJC Scopus subject areas

  • Inorganic Chemistry

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