Non-equilibrium and non-linear stationary state in thermoelectric materials

TL;DR

This paper reveals that the thermoelectric figure of merit Z varies with size and exhibits non-linear temperature profiles in stationary states, challenging the traditional view of Z as a constant.

Contribution

It demonstrates that Z is not a fixed material constant but depends on size and position, based on new measurements using the Harman method.

Findings

Z has large size dependence

Non-linear temperature distribution observed

Z varies with position in the material

Abstract

Efficiency of thermoelectric materials is characterized by the figure of merit Z. Z has been believed to be a peculiar material constant. However, the accurate measurements in the present work reveal that Z has large size dependence and a non-linear temperature distribution appears as stationary state in the thermoelectric material. The observation of these phenomena is achieved by the Harman method. This method is the most appropriate way to investigate the thermoelectric properties because the dc and ac resistances are measured by the same electrode configuration. We describe the anomalous thermoelectric properties observed in mainly (Bi,Sb)2Te3 by the Harman method and then insist that Z is not the peculiar material constant but must be defined as the physical quantity dependent of the size and the position in the material.