Low-Temperature Thermal Expansion of Copper

A rotating single-crystal back-reflection x-ray diffraction technique has been used to measure the thermal expansivity of copper. Values of the linear thermal expansion coefficient are derived at low temperature where disagreement exists in the literature. A possible decrease in the Grüneisen parameter $\gamma$ for copper exists near 40°K. The decrease reported in the present work is much less marked than previously reported from capacitor dilatometer work, however. It is suggested that large apparent decreases in $\gamma$ at low temperature reported from similar measurements on Al, Fe, Ag, and KBr may be in error.