THE COEFFICIENT OF THERMAL EXPANSION OF VARIOUS CUBIC METALS BELOW 100 °K

Abstract

Measurements have been made of the coefficient of linear thermal expansion, α, of Cu, Ag, Au, Al, α-Fe, and Ni at temperatures below 100 °K using an interferometric method in which the spacer between the optical flats of a Fabry–Perot-type interferometer was made of the material studied. The lowest temperatures at which values of α are given are about 20 °K (Cu, Ag), 11 °K (Au), 25 °K (Al, Fe), and 32 °K (Ni). The results are discussed in terms of the Gruneisen parameter γ which, for Cu, Ag, and Au, is approximately constant at high temperatures, but tends to rise slightly as the temperature is reduced towards the lowest temperatures of measurement. For Al, a correction for the electronic contribution is applied below 40 °K to deduce the lattice contribution γL, which rises more spectacularly at low temperatures than the results for the noble metals. For Fe, separation of α into two contributions, one from the lattice and one from the combined magnetic and electronic effects, may be made, giving γL = 1.45; the combined magnetic and electronic contribution is very small.