Thermopower of Pure Aluminum

The thermopower of 99.999% pure, polycrystalline aluminum has been measured from 4.2 to 300^∘{}K using Pb as the standard, and from 300 to above 700^∘{}K using Au and Cu as alternative standards. The thermopower is negative at all temperatures with a phonon-drag peak occurring at about 75^∘{}K. From 200 to 300^∘{}K the thermopower S is well-described by the relation S=-2.34×10^-3T-284T_μV/^∘{}K. The thermopowers determined against Au and Cu are not quite the same above 450^∘{}K, showing a difference of about 0.1 {μ}V/^∘{}K at 700^∘{}K. However, each set of data is consistent with the form S=-AT-B/T (A and B are positive constants); and a reasonable average for the two standards is given by S=-3.00×10^-3T-229T_μV/^∘{}K, for $T>300$^∘{}K. These two terms are interpreted as representing diffusion thermopower and phonon-drag thermopower contributions, respectively. If this interpretation is correct, it represents the first clear example of a nonzero phonon-drag thermopower in a metal at temperatures above 300^∘{}K.