Measuring Thermal Conductivity of Thermoelectrics: Bismuth Telluride
Thermoelectric materials are those in which a temperature difference causes an electrical potential, or vice versa. Thermal conductivity is an important parameter of thermoelectric material performance: large thermal conductivity reduces the effective temperature difference on either side of the material and reduces performance. The thermal conductivity of the thermoelectric is thus considered a critical performance attribute of the material.
Figure 1. Graphical illustration of the Seebeck effect.
Thermoelectric effects fall into three categories: The Seebeck effect, where applied temperature difference across the sample causes the formation of an electric potential, the Peltier effect, where an applied electric potential causes a temperature difference to form, and the Thompson effect, where a conductor transmitting current will heat or cool. These effects are closely related, and given information about the Seebeck behavior of a material (via the Seebeck coefficient), it is possible to calculate the Peltier and Thompson coefficients of that material. A more technical discussion of these phenomena, including complete derivations of thermoelectric equations governing these behaviors, may be found here.
Thermoelectric materials are currently used mainly in niche cooling applications, such as temperature maintenance of lasers in scientific equipment. However, as the result of increased world concern about global warming, development of new, less expensive thermoelectric materials has begun to improve automotive and power plant efficiency, among other things.
Bismuth Telluride is a considered a classic thermoelectric material with a Seebeck coefficient of −287 μV/K at 54 °C, and its derivatives are in wide use both in industry and in research. Here at C-Therm we measured its thermal conductivity with a C-Therm TCi sensor across three tests of five data samples each. Each test had a relative standard deviation of <0.8% and overall there was a deviation of <1.5% across three tests. The mean of these tests agreed with the literature accepted value of Bi2Te3 thermal conductivity within <1%.