The Thermal Resistivity and the Wiedemann-Franz Ratio of Single Crystal Zinc

The thermal resistivities at 57^∘{}C are measured for thirteen large, strain-free, single crystals of zinc. The guard tube method is used with the heat applied at the center of the specimen. The results show definitely that the thermal resistivity obeys the Voigt-Thomson symmetry relation. The principal resistivities are ω₀=0.991 and ω₉₀=0.936 cm deg. C/watt, with the ratio ω₀ω₉₀=1.058⁸. The close agreement of this value with the ratio of the principal electrical resistivities previously determined in this laboratory shows that the W-F ratio is the same for all orientations of the zinc crystal. The value of this ratio is 7.15×{}10^-6 watt ohm/deg. C at 57^∘{}C and agrees within 11 percent with the value predicted by the Sommerfeld theory. The two principal thermal conductivities are λ₀=1.009² and λ₉₀=1.068⁴ watts/cm deg. C at 57^∘{}C. Some observations are included on "optically mosaic" crystals and on the effects of permanent strain on the single and mosaic crystals.