THERMOELECTRIC PROPERTIES OF FINE-GRAINED (75-PERCENT-SB2TE3-25-PERCENT-BI2TE3) P-TYPE AND (90-PERCENT-BI2TE3-5-PERCENT-SB2TE3-5-PERCENT-SB2SE3) N-TYPE ALLOYS

The thermoelectric properties of fine-grained alloys prepared by either cold pressing and sintering or hot pressing in the range 5-50-mu-m are compared with single-crystal best-direction values. It is shown that for the p-type alloy, almost the entire thermoelectric properties are recovered, i.e. the figure of merit for the finest grain size is almost the same as the best single-crystal value. The same trend is observed in the n-type alloy except that 90% of the single-crystal figure of merit is recovered. These results are discussed in terms of a model which suggests that degradation of favourable thermoelectric properties by powdering the alloys is compensated by (1) decrease of thermal conductivity due to scattering of phonons at grain boundaries for grain sizes that are comparable to the mean free path of phonons; and (2) retention of some of the anisotropic properties of the single crystal in the fine-grained compacts.