Exploiting waste heat by means of thermoelectric generators has long been proposed as one of the ways to meet the worlds rising energy demands. However, thermoelectric materials still need improvements to be cost-effective in most applications. Higher efficiency materials could be obtained by optimizing the materials through functionality grading to meet the changing temperature conditions within a thermoelectric leg in operation.

The physical parameters that influence the efficiency of a thermoelectric material are all strongly temperature dependent, and consequently the efficiency of a homogeneous material peaks in a narrow temperature interval. By grading these parameters though the material, the temperature at which the efficiency peaks can also be graded.

Opposed to most other techniques for functionality grading, graded materials can be achieved in one step though Czochralski or Bridgman/Stockbarger synthesis. It has previously been shown that thermoelectric materials graded in either composition, and thereby band gap [1], or doping [2] can be prepared in this way, but by combining the two effects a potentially significant improvement in efficiency should be achievable.

1. Christensen, M., et al., Fast Preparation and Characterization of Quarternary Thermoelectrics Clathrates. Chem. Mater, 2009. 21(1): p. 122-127.

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1. Exploiting Inherent Thermodynamic Effects in Crystal Growth to Achieve Functionally Graded Thermoelectrics.