Thermal Expansion of Tellurium

Coefficients of thermal expansion α‖c and α⟂c have been measured from 1.6 to 300 °K in a capacitor cell and from 300 to 500 °K in a Perot‐Fabry interferometer. In the whole temperature range α‖c is negative and α⟂c positive. The negative sign of α‖c must be considered mainly as a result of the elastic anisotropy of tellurium, since the Grüneisen parameters γ‖c(T) and γ⟂c(T) are almost equal and positive. The decrease of γ‖c(T) and the increase of γ⟂c(T) at low temperatures is attributed to an anisotropy in the strain dependence of low lying phonon frequencies and can be qualitatively understood by inspection of the lattice and its similarity to the hexagonal primitive lattice.