Colligative thermoelectric transport properties in n-type filled CoSb₃ determined by guest electrons in a host lattice

Among many kinds of thermoelectric materials, CoSb₃ has received exceptional attention for automotive waste heat recovery. Its cage structure provides an ideal framework for the realization of phonon-glass electron-crystal strategy, and there have been numerous reports on the enhanced thermoelectric performance through the independent control of the thermal and electrical conductivity by introducing fillers into its cage sites. Herein, we report colligative thermoelectric transport properties in n-type CoSb₃ from the viewpoint of "guest electrons in a host lattice." Both the Seebeck coefficient and the charge transport properties are fundamentally determined by the concentration of the guest electrons, which are mostly donated by the fillers, in the conduction band of the host CoSb₃. Comparing this observation to our previous results, colligative relations for both the Seebeck coefficient and the mobility were deduced as functions of the carrier concentration, and thermoelectric transport constants were defined to predict the power factor in filled CoSb₃. This discovery not only increases the degree of freedom for choosing a filler but also provides the predictability of power factor in designing and engineering the n-type filled CoSb₃ materials.