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)2Te3 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.