Detrimental Effects of Doping Al and Ba on the Thermoelectric Performance of GeTe

Abstract : GeTe-based materials are emerging as viable alternatives to toxic PbTe-based thermoelectric materials. In order to evaluate the suitability of Al as dopant in thermoelectric GeTe, a systematic study of thermoelectric properties of GeAlTe ( = 0⁻0.08) alloys processed by Spark Plasma Sintering are presented here. Being isoelectronic to GeInTe and GeGaTe, which were reported with improved thermoelectric performances in the past, the GeAlTe system is particularly focused (studied both experimentally and theoretically). Our results indicate that doping of Al to GeTe causes multiple effects: (i) increase in -type charge carrier concentration; (ii) decrease in carrier mobility; (iii) reduction in thermopower and power factor; and (iv) suppression of thermal conductivity only at room temperature and not much significant change at higher temperature. First principles calculations reveal that Al-doping increases the energy separation between the two valence bands (loss of band convergence) in GeTe. These factors contribute for GeAlTe to exhibit a reduced thermoelectric figure of merit, unlike its In and Ga congeners. Additionally, divalent Ba-doping [GeBaTe ( = 0⁻0.06)] is also studied.
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Bhuvanesh Srinivasan, Alain Gellé, Jean-François Halet, Catherine Boussard-Plédel, Bruno Bureau. Detrimental Effects of Doping Al and Ba on the Thermoelectric Performance of GeTe. Materials, MDPI, 2018, 11 (11), pp.2237. ⟨10.3390/ma11112237⟩. ⟨hal-01926269⟩

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