Thermal expansion at low temperatures of hexagonal metals: Mg, Zn and Cd

Abstract

Measurements have been made between 2 and 30°K of the linear thermal expansion of single crystals of Mg, Zn and Cd, both parallel (⌋) and normal (Ι) to the hexad axis. Values have also been obtained at liquid oxygen temperatures and at room temperature which agree with previous data. (i) For Mg, the linear coefficient α_Ι is larger than α_∥ below 30°K, and at the lowest temperatures (< 10°K) α_∥ = (0·9₅ T + 0·021T ³) × 10⁻⁹ °K⁻¹ and α_∥ = (1·2₅ T + 0·036T ³) × 10⁻⁹ °K⁻¹; the Grüneisen parameter, γ, remains between 1·4 and 1·5. (ii) In zinc, α_∥ is negative between 8 and 70°K; α_∥ is always positive and increases very rapidly between 10 and 40°K. γ has a value of 2·0 at room temperature and below 10°K but has a maximum of about 2·8 at θ/15. (iii) For cadmium, α_∥ is negative from 5 to 40°K, but below this a positive term, assumed to be due to the electron gas, predominates; α_∥ varies with temperature much as in zinc. γ is about 2·3 at high and low temperatures and reaches a maximum of 3·4 at θ/15.