ABSTRACT
Since the discovery of semiconductor thermoelements, there has been much effort to enhance the efficiency of thermoelectric (TE) devices. Along with efforts to increase a material’s figure of merit, the use of functionally graded materials (FGM) offers other ways to further improve device performance. Graded TEs are characterized by a macroscopic gradient in their functional properties, caused by spatial variation of the composition or microstructure. Also noncontinuously graded elements are considered FGM since they lead to the same functional effect. TE effects are caused by coupling between heat and charge transport of the electronic “fluid”. The description on a mesoscopic level is based on a stationary picture where all the thermodynamic potential functions are clearly defined, though the system itself produces dissipation. Since the inherent relaxation times are much smaller than the timescale of the varying potentials, this description is also a definition of a quasi-static process.
