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 $S=-2.34\mathrm{}\times {10}^{-3\mathrm{}}T-\frac{284}{T_{\mu }}$V/°K. The thermopowers determined against Au and Cu are not quite the same above 450°K, showing a difference of about 0.1 μV/°K at 700°K. However, each set of data is consistent with the form $S=-AT-\frac{B}{T}$ ($A$ and $B$ are positive constants); and a reasonable average for the two standards is given by $S=-3.00\mathrm{}\times {10}^{-3\mathrm{}}T-\frac{229}{T_{\mu }}$V/°K, for $T>\mathrm{}300\mathrm{}$°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.