Tuning the Vacancy Concentration in Lithium Germanium Antimony TelluridesInfluence on Phase Transitions, Lithium Mobility, and Thermoelectric Properties

• Published in: Chemistry of materials Vol. 30; no. 21; pp. 7970 - 7978
• Main Authors: Schwarzmüller, Stefan, Jakob, Matthias, Nentwig, Markus, Schröder, Thorsten, Kuhn, Alexander, Düvel, Andre, Heitjans, Paul, Oeckler, Oliver
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13.11.2018
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.8b03609

In the solid solution series Li2–x Ge3+1/2x Sb2Te7 and Li2–x Ge11+1/2x Sb2Te15 (0 ≤ x ≤ 2), the heterovalent substitution gradually changes the vacancy concentration on the cation position from 0% (for x = 0) to 14.3% and 6.67%, respectively. Fewer vacancies extend the stability range of the rocksalt-type high-temperature phase to lower temperatures, which is favorable for thermoelectric applications. Further differences in thermoelectric properties correlate with the Li/Ge ratio. The phononic part of thermal conductivity decreases with increasing Li content and all Li-containing compounds exhibit enhanced thermoelectric figures of merit zT compared to their Li-free parent phases with a maximum zT value of 1.9 for LiGe3.5Sb2Te7 at 450 °C. 7Li solid state NMR reveals high Li mobility at elevated temperatures. Thus, lithium germanium antimony tellurides can be considered as new member of phonon-liquid electron-crystal (PLEC) thermoelectric materials with superior thermoelectric properties.