1. Introduction
Thermoelectric materials can directly convert thermal energy into electricity or vice versa, through the
so called Seebeck effect and Peltier effect, respectively. The phenomena are the basis of the operation of
thermoelectric generators (TEG) and thermoelectric refrigerators (TER). Practical TEG or TER employs
one or more thermoelectric modules, in which thermoelectric materials are used as thermoelectric
elements. A thermoelectric module is composed of several pairs of p-type and n-type thermoelectric
elements connected electrically in series but thermally in parallel. The performance of a thermoelectric
element can be evaluated from the material's electrical power factor, P = S2
/ρ, or the dimensionless figure
of merit, ZT = S2
T/ρκ, where S is the Seebeck coefficient, ρ is the electrical resistivity, κ is the thermal
conductivity, and T is the absolute temperature [1,2,3].
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