Thermopower of Pure Aluminum

Abstract

The thermopower of 99.999% pure, polycrystalline aluminum has been measured from 4.2 to 300\ifmmode^\circ\else\textdegree\fi{}K using Pb as the standard, and from 300 to above 700\ifmmode^\circ\else\textdegree\fi{}K using Au and Cu as alternative standards. The thermopower is negative at all temperatures with a phonon-drag peak occurring at about 75\ifmmode^\circ\else\textdegree\fi{}K. From 200 to 300\ifmmode^\circ\else\textdegree\fi{}K the thermopower $S$ is well-described by the relation $S=\ensuremath{-}2.34\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}T\ensuremath{-}\frac{284}{{T}_{\ensuremath{\mu}}}$V/\ifmmode^\circ\else\textdegree\fi{}K. The thermopowers determined against Au and Cu are not quite the same above 450\ifmmode^\circ\else\textdegree\fi{}K, showing a difference of about 0.1 \ensuremath{\mu}V/\ifmmode^\circ\else\textdegree\fi{}K at 700\ifmmode^\circ\else\textdegree\fi{}K. However, each set of data is consistent with the form $S=\ensuremath{-}AT\ensuremath{-}\frac{B}{T}$ ($A$ and $B$ are positive constants); and a reasonable average for the two standards is given by $S=\ensuremath{-}3.00\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}T\ensuremath{-}\frac{229}{{T}_{\ensuremath{\mu}}}$V/\ifmmode^\circ\else\textdegree\fi{}K, for $T>300$\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K.