Some Electrical Properties of Spectroscopically Pure Zinc Crystals

With single crystal specimens of spectroscopically pure zinc (99.9999 percent zinc), the Thomson coefficient at 49.5°C has been measured as a function of orientation. A very accurate confirmation of the Voigt-Thomson symmetry relation is obtained, the principal values of the Thomson coefficient being:${\sigma }_{\perp }=0.86\mathrm{}\times {10}^{-6\mathrm{}}$cal./coul./deg., and ${\sigma }_{\parallel }=0.34\mathrm{}\times {10}^{-6\mathrm{}}$ cal./coul./deg. The thermal e.m.f. of these same specimens against copper has been determined as a function of orientation throughout the temperature range -180° to 200°C. From these data, the values of the Peltier coefficient, the Thomson coefficient, and the difference in principal Thomson coefficients have been computed as functions of temperature by means of the relations given by the Kelvin thermodynamical theory of thermoelectricity. The values of the Peltier coefficient of ${\mathrm{Zn}}_{\perp }$ against ${\mathrm{Zn}}_{\parallel }$ thus obtained are: $\pi =658\mathrm{}$ microvolts at 49.5°C and $\pi =1080\mathrm{}$ micro-volts at 125°C. For the difference in the principal Thomson coefficients, the values are: ${\sigma }_{\perp }-{\sigma }_{\parallel }=0.58\mathrm{}\times {10}^{-6\mathrm{}}$ cal./coul./deg. at 49.5°C and ${\sigma }_{\perp }-{\sigma }_{\parallel }=1.20\mathrm{}\times {10}^{-6\mathrm{}}$ cal./coul./deg. at 125°C. The predictions of the Kelvin theory regarding ${\sigma }_{\perp }-{\sigma }_{\parallel }$ are thus found to be in agreement with the direct determinations by Ware and the writer. The Voigt-Thomson law is found to hold also in the case of thermoelectric power and the other thermoelectric properties to which it should apply. The dependence of resistivity on temperature has been investigated for the temperature range -170° to 25°C. The average value of the temperature coefficient of resistivity obtained is: $\alpha =4.058\mathrm{}\times {10}^{-3\mathrm{}}$. For comparison purposes, a direct determination of the Thomson coefficients of single cyrstal specimens of Kahlbaum's best zinc at 49.5°C has also been made, as well as a study of the dependence of their resistivities on temperature. For this less pure zinc, the principal values of the Thomson coefficient are: ${\sigma }_{\perp }=0.91\mathrm{}\times {10}^{-6\mathrm{}}$ cal./coul./deg. and ${\sigma }_{\parallel }=0.38\mathrm{}\times {10}^{-6\mathrm{}}$ cal./coul./deg. For the temperature coefficient of resistivity, the average value is: $\alpha =4.009\mathrm{}\times {10}^{-3\mathrm{}}$. A variation in the values of $\alpha$ for specimens of the same grade of zinc is observed which is considerably greater than can be attributed to experimental error.