熱電変換材料の無次元性能指数における理論的最大値の物質依存性

抄録

  The electronic structures and thermoelectric properties of 12 parent compounds for thermoelectric materials were compared, from first-principles calculations and numerical solutions of Boltzmann transport equations. Carrier doping level dependences of the maximum possible thermoelectric figures of merit Z_eT were calculated, in the limit of zero phonon thermal conductivity and infinite electron relaxation time. High enough Z_eT was only observed in semiconductors with finite bandgaps. Higher Z_eT was expected in compounds with steep density of states at the band edge. Such electronic structures were found in transition metal compounds, especially in transition metal oxides. We evaluated the temperature dependence of electron relaxation time, by combining calculation results with experimental transport properties. These analyses reduce the number of experiments to search for new thermoelectric materials, and will reveal the nature of various electron scattering centers within the thermoelectric materials.