Abstract
The Onsager–de Groot–Callen transport theory, implemented as a network model, is used to simulate the transient Harman method, which is widely used experimentally to determine all thermoelectric transport coefficients in a single measurement setup. It is shown that this method systematically overestimates the Seebeck coefficient for samples composed of two different materials. As a consequence, the figure of merit is also overestimated, if the thermal coupling of the measurement setup to the environment is weak. For a mixture of metal and semiconductor particles near metal percolation the figure of merit obtained by the Harman method is more than 100% too large. For a correct interpretation of the experimental data, information on composition and microstructure of the sample are indispensable.
Highlights
Thermoelectric materials are important for energy harvesting, especially from waste heat1,2
The Seebeck coefficient and the heat conductivity measured via the Harman method depend on the current, which was applied before the measurement of Vα and deviate strongly from the open circuit values, eqs. [30] and [31]
A simple but powerful simulation model has been derived that describes all thermoelectric responses according to the Onsager-de Groot-Callen transport theory
Summary
Thermoelectric materials are important for energy harvesting, especially from waste heat. Since analytic calculations are restricted to simple compounds, numerical models have been developed in order to describe inhomogeneous materials These models are based on the Onsager-de GrootCallen theory, most of them do not fully describe the thermoelectric effects, since they do not include Joule heat and/or Peltier heat. In this paper a simple and coherent way to discretize the Onsager transport theory for thermoelectric materials will be used, which includes all relevant effects and time-dependencies It can be seen as a version of the finite difference method reviewed in. The temperatures of the electrodes are determined by Joule heating, Peltier effect and heat exchange with the environment In general they differ from THB and depend on the current direction
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