ae9b02015_si_001.pdf (288.97 kB)
Critical Analysis of Single Band Modeling of Thermoelectric Materials
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 DasguptaStudy 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.