Amorphous thermoelectrics

Previous calculations for one of the half-Heusler alloys have indicated that the mean free path may sometimes be greater for phonons than for 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 the amorphous form to be superior. The most important quantity is undoubtedly the effective mass of the charge carriers but it appears that this quantity is unlikely to be large enough to make the free path length of the carriers sufficiently small, at room temperature, in any good thermoelectric material. On the other hand, it seems quite possible that amorphous material may be preferred for high-temperature thermoelectric generation.