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Critical Analysis of Single Band Modeling of Thermoelectric Materials

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Version 2 2020-02-21, 21:29
Version 1 2019-12-08, 19:43
journal contribution
posted on 2020-02-21, 21:29 authored by Harshita Naithani, Titas Dasgupta
Study of the electronic band structure of thermoelectric (TE) materials is fundamental to both its understanding and further development. Currently theoretical models which assume a single-band-based charge transport are utilized due to their predictive capabilities and ease of implementation. However, most good thermoelectric materials have complex band structures with multiple bands near the band edge. The extent of applicability of single-band models in such systems is questionable and forms the objective of this study. To check this, we have chosen five well-known TE materials and modeled their room temperature properties using the single parabolic band (SPB) model and the single Kane band (SKB) model. The room temperature experimental data for these materials were extracted from literature reports, and the analysis was carried out on a relatively large sample set (with over 350 data points spread across the various materials). Our analysis indicates the failure of single-band models in situations where multiple near-degenerate bands are present close to the band extrema. The associated errors are in the estimated density of states effective mass (mD*), Lorenz number (L), and lattice thermal conductivity (κL), which in turn result in erroneous predictions of the optimum charge carrier concentration and zT values. We also find that identifying whether the band edge is parabolic is difficult from a visual comparison of the SPB and SKB Pisarenko plots since the observed variations are well within the acceptable limits of experimental error. To overcome this problem, we propose an error analysis technique which can be used to find the best fit model. The error analysis can also be useful in identifying the dominant charge carrier scattering mechanism as shown from our study. Overall, our work highlights the need for implementation of multiband modeling while working with materials with complex band structures.

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