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Schwarzmüller, Stefan; Jakob, Matthias; Nentwig, Markus; Schröder, Thorsten; Kuhn, Alexander; Duevel, Andre; Heitjans, Paul and Oeckler, Oliver (2018): Tuning the Vacancy Concentration in Lithium Germanium Antimony Tellurides-Influence on Phase Transitions, Lithium Mobility, and Thermoelectric Properties. In: Chemistry of Materials, Vol. 30, No. 21: pp. 7970-7978

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In the solid solution series Li2-x Ge3+1/2xSb2Te7 and Li2-xGe11+1/2xSb2Te15 (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 degrees C. Li-7 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.

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