Thermoelectric Power of Dilute Copper Alloys

Abstract

The thermoelectric power of dilute binary copper alloys containing one atomic percent Zn, Ge, Cd, In, Sn, and Sb was determined over the temperature range extending from about 8\ifmmode^\circ\else\textdegree\fi{}K to 320\ifmmode^\circ\else\textdegree\fi{}K. The thermoelectric powers were obtained by measuring the thermoelectric emf's of thermocouples formed of the alloys and pure copper. The absolute thermoelectric power of pure copper was obtained from measurements on a pure copper versus lead thermocouple.The results are analyzed in terms of the Friedel theory. It is found that above 40\ifmmode^\circ\else\textdegree\fi{}K satisfactory agreement with that theory can be obtained only if it is assumed that phonon drag makes a significant contribution to the thermoelectric power in the pure material below room temperature. The magnitude and temperature dependence of this assumed phonon drag contribution are in satisfactory agreement with theoretical estimates. Moreover, the effect of alloying on this phonon drag contribution also agrees with theoretical estimates based on reasonable models. In the temperature range below about 40\ifmmode^\circ\else\textdegree\fi{}K we have not been able to give a satisfactory interpretation of our results. Our measurements show that near 40\ifmmode^\circ\else\textdegree\fi{}K the absolute thermoelectric power of pure copper reverses sign, becoming negative, and attains an anomalously low minimum of about - 1.8 \ensuremath{\mu}v/degree near 10\ifmmode^\circ\else\textdegree\fi{}K. If this behavior is due to the presence of minute amounts of impurities in the pure copper which give rise to a thermoelectric anomaly associated with the appearance of a resistivity minimum, then our results can be interpreted without much difficulty. However, the residual resistivity of the pure copper was so low that we do not believe that the low-temperature thermoelectric anomaly can be attributed to the presence of impurities.A research program on thermoelectric properties of dilute alloys which should shed further light on these questions is outlined.