Ineffectiveness of energy filtering at grain boundaries for thermoelectric materials

Abstract

We use a one-band effective mass model within the Landauer formalism to investigate the influence of double Schottky barriers on the thermoelectric coefficients. It is assumed that these double Schottky barriers arise due to trapping states in grain boundaries. Such barriers can cause an energy filtering effect, which is widely believed to advance thermoelectric efficiencies. We show that for low doping concentrations the Seebeck coefficient is indeed increased due to energy filtering effects, whereas the electric conductivity is strongly decreased. The resulting power factor is also decreased. For higher doping concentrations, which are necessary for large electric conductivities and thus reasonable ZT values, the double Schottky barriers are very small and have therefore an insignificant impact on the thermoelectric parameters. Consequently, there is no significant influence of grain boundaries on ZT values due to additional electrostatic barriers. This does not preclude that other mechanisms at grain boundaries, such as additional scattering due to disorder, can have a positive impact on the power factor.

Fine‐Grained and Nanostructured AgPbmSbTem+2 Alloys with High Thermoelectric Figure of Merit at Medium Temperature

“…[ 30 ] This phenomenon was confi rmed by previous work, [31][32][33][34] with the exception of a special case. [ 35 ] Although the boundary-scattering would affect electron transport, its effect can be weakened partially by the improvement of electrical conductivity benefi ting from the elimination of excessive Pb nanoparticles. As a result, an enhanced Seebeck coeffi cient and reduced electrical resistivity can be achieved at the same time.…”

Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb

“…According to theoretical considerations, energy filtering can arise from extended barriers such as heterostructures, nanocomposites, nanoinclusions, or grain boundaries. [9][10][11][12][13][15][16][17] A. Electronic structure calculations…”

“…By introducing potential barriers or strongly energy-dependent scattering mechanisms, low-energetic carriers can be blocked, greatly enhancing the Seebeck coefficient. 7,[9][10][11][12][13][14][15][16][17][18] ZnSb has been known as a thermoelectric material for a long time. 19 When Caillat reported a figure of merit of 1.4 for Zn 4 Sb 3 in 1997, that composition got the most attention due to the remarkably low thermal conductivity.…”

Enhanced room-temperature thermoelectric performance of In-doped ZnO:Al thin films through prefabricated layer doping method

“…However, it will obviously reduce when the nanorods become sparse or disappear. In some reports, [25,26] the Seebeck coefficient increases when interface scattering is added. Hence, the increase in the Seebeck coefficient is due to the increase in grain size and interface scattering.…”