Effect of linear temperature dependence of thermoelectric properties on energy conversion efficiency

New thermal rate equations were developed by taking the temperature dependences of the electrical resistivity rho and thermal conductivity kappa of the thermoelectric (TE) materials into the thermal rate equations on the assumption that they vary linearly with temperature T. The relative energy conversion efficiency eta/eta(0) for a single TE element was formulated by approximate analysis, where eta and eta(0) are the energy conversion efficiencies derived from the new and conventional thermal rate equations, respectively. Applying it to Si-Ge alloys, the temperature dependence of rho is stronger than that of kappa, so the former has a more significant effect on eta/eta(0) than the latter. However, the degree of contribution from both of them to eta/eta(0) was a little lower than 1% at the temperature difference Delta T of 600 K. When the temperature dependence of kappa was increased to become equal to that of rho, however, it was found that eta/eta(0) is increased by about 10% at Delta T = 600 K. It is clarified here that the temperature dependences of rho and K are also important factors for an improvement in eta. (C) 2008 Elsevier Ltd. All rights reserved.