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

Thermoelectric properties such as the figure of merit Z and the temperature distribution in sample have been measured by the Harman method. The efficiency of thermoelectric materials is characterized by Z, which has long been believed to be a specific material constant. However, accurate measurements reveal that Z is largely dependent on sample size, and a non-linear temperature distribution appears as a stationary state in thermoelectric material. We describe the experimental results of anomalous thermoelectric properties observed primarily in (Bi,Sb)(2)Te-3 and then conclude that Z is not a specific material constant, but must be defined as a physical quantity dependent on the size and the position in the material. It is also pointed out that the obtained results are important for improving thermoelectric efficiency in practical applications. (C) 2004 Elsevier Ltd. All rights reserved.