On conditios of high figure of merit and methods of search for promising superlattice thermoelectric materials

TL;DR

This paper rigorously calculates the figure of merit for superlattice thermoelectric materials considering real 3D effects and Fermi surface openness, proposing new search methods using magnetic fields to identify promising materials.

Contribution

It introduces a detailed calculation of thermoelectric performance considering nonparabolic spectra and proposes four novel magnetic field-based search methods for superlattice thermoelectric materials.

Findings

Figure of merit increases with Fermi surface openness.

Thermoelectric performance is sensitive to layer spacing.

Magnetic field methods can identify promising materials.

Abstract

This paper presents a rigorous calculation of the figure of merit of superlattice thermoelectric material (SL TEM) with regard to real three-dimensionality and nonparabolicity of its energy spectrum with the arbitrary level of openness of its Fermi surface (FS).It is shown that the figure of merit of SL TEM in the temperature range of 300-500K is drastically increased with increasing level of openness of FS. However, due to the presence of lattice component of thermal conductivity the figure of merit of SL TEM is rather responsive to the distance between the layers and drastically drops with its increase. Besides, for the same material, coefficient of performance of a refrigerator in the framework of its simplest model was calculated. It was established that if material band spectrum is described by the Fivaz model, the coefficient of performance is drastically increased with increasing the level of openness of FS and in case of transient FS it reaches 1.9 between the temperatures of 300 and 230K. However, as the distance between the layers of SL TEM increases 2 times, it drops to 0.4 Based on the obtained criteria, four methods of search for promising SL TEM with the use of quantizing magnetic fields are proposed.