The Figure of Merit in Amorphous Thermoelectrics

In some semiconductors, the mean free path can be greater for the phonons than for the charge carriers. When this is the case it is likely that the material will display a higher thermoelectric figure of merit in the amorphous rather than the crystalline form. Here we determine the general conditions that must hold for an amorphous material to be promising for thermoelectric applications. The most important quantity is undoubtedly the effective mass of the charge carriers. At room temperature it appears that this quantity is unlikely to be large enough for our purposes in any good thermoelectric material presently known. On the other hand, it seems quite possible that amorphous material may be useful in high-temperature thermoelectric generation. We suggest that our ideas may be demonstrated in amorphous or fine-grained skutterudites and half-Heusler alloys.