A New Look At Defining The Thermodynamic In Thermoelectrics

Many phenomena in physics, though well-known, are not necessarily widely understood as is the case with thermoelectricity. Thermoelectricity is the phenomena that harnesses waste heat by coupling heat flux to build an electric current.

Understanding such phenomena is important in order to leave the door open for discovering novel manifestations of them.

Even today physicists working in the area of thermoelectricity continue to ask fundamental questions about the underlying physical process. For example, in a recent study, a team based in France questioned the nature of the force that puts electrons to work when a temperature difference is applied across a thermoelectric material.

Now, Henni Ouerdane, affiliated to the Russian Quantum Center near Moscow, and colleagues have published in The European Physics Journal Plus a study showing that the force that puts electrons to work to harness the waste heat is linked to the ability of electrons to diffuse through the material.

Potential applications in the field of electrical power production from waste heat include thermoelectric devices designed to boost power over a range spanning ten orders of magnitude: typically from microwatts to several kilowatts.

One of the key factors in thermoelectricity is a measure of the strength of the mutual interaction between electric charge transport and heat transport, referred to as the Seebeck coefficient. In physical terms, this coefficient is related to the gradient of the system’s electrochemical potential. In this study, the authors analyze the relationship between the thermoelectric power and the electrochemical potential in the thermoelectric system.

In particular, they studied this in a semiconductor with low levels of impurity, as a model for observing the Seebeck coefficient. They then establish the link between this first model and a second, which uses the laws of thermodynamics to determine how the system behaves when it is not at equilibrium. They demonstrate that the electrical current resulting from thermoelectric effects can be directly formulated from the equations governing drift-diffusion of electrons at the macroscopic scale.

In their analysis of the relationship between the thermoelectric power and the relevant potentials in the thermoelectric system they are able to clarify the definitions of the chemical and electrochemical potentials. Then they can show with a proper consideration of each potential how one may derive the Seebeck coefficient of a non-degenerate semiconductor without the need to introduce a contact potential as often seen currently.

The group can also demonstrate that the phenomenological expression of the electrical current resulting from thermoelectric effects may be directly obtained from the drift-diffusion equation.

This work could very well simplify the research into thermoelectrics by allowing the math to explore many ideas without the time and expense of experimentation.

Thermoelectrics is a field in need of some breakthroughs. This work just might get the field moving faster toward using some of that heat that now is just warming up the atmosphere.