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WEB Determining the optimal carrier concentrations and compositions in p-type Mg2(Si,Sn) using exact efficiency

Friday (25.09.2020)
10:40 - 10:55 F: Functional Materials, Surfaces, and Devices 1
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Mg2(Si,Sn) based thermoelectric materials are quite popular for its availability, low cost, lightweightedness and good figure of merit (zT) of the n-type material. Unfortunately, so far p-type Mg2(Si,Sn) has only shown a maximum zT of about 0.6. Therefore, optimisation of composition and carrier concentration is necessary to find the best properties. Conventionally, the zT mapping between composition and carrier concentration is used to find the optimum parameters. However, zT could be misleading, especially when the TE properties are strongly temperature (T) dependent, as zT is based on the constant property assumption. To resolve this issue we employed device efficiency as a direct measure of performance by combining a one dimensional, full T dependent device performance calculation routine with a physics based material model. Here, a Single Parabolic Band (SPB) model was assumed for the material, with an effective mass linearly dependent on composition, and acoustic phonon and alloy scattering were assumed as dominant scattering mechanisms for the charge carriers. The optimum x in Mg2Si1-xSnx was identified as x ≈0.65 for T_cold= 300K and T_hot= 500K (which is well within the validity limits of SPB), while with zT mapping (at 500K), it was found to be x ≈0.55, a difference of about 20%. Also, the optimum n differs between the two cases. Our approach opens up a new strategy to not only accurately refine the search for better materials but also provides a way to directly correlate the material physics parameters to device performance, bringing up a new outlook towards thermoelectric material development.

Prasanna Ponnusamy
German Aerospace Center (DLR)
Additional Authors:
  • Prof. Eckhard Müller
  • Dr. Johannes de Boor