The thermal expansion of sodium fluoride at low temperatures

Abstract

Measurements of the linear thermal expansion coefficient α of sodium fluoride between 20 and 273°K are reported. The observations were made using the interferometric apparatus of James and Yates (1965). The Grüneisen parameter γ = βV/C _v X _T has been calculated, and used to calculate the parameter γE occurring in the Mie-Grüneisen equation of state of solids. γM _E was found to be much less dependent upon temperature than γ. The two parameters were used, together with results stemming from the vibrational frequency distribution calculated by Karo (1959), in applying the expression for α derived by Pautamo (1963) using Taylor expansions. Similar calculations were performed for rubidium bromide, and in both cases a satisfactory degree of self-consistency was observed.