THE THERMAL EXPANSION OF COPPER AT LOW TEMPERATURES,

The thermal expansion of copper has been determined at temperatures down to 2 K by means of an electrical capacitance technique. By measuring three-terminal capacitances in a ratio-transformer bridge length changes smaller than 10 to the minus 9 power cm can be detected in the capacitor-expansion cell. The linear expansion coefficient is given for below 10 K. These terms, identified respectively as electronic e and lattice l in origin, lead to the following values of the Gruneisen parameter gamma sub e 0.630.06, gamma sub l 1.720.03 gamma sub 0. Gamma sub e is compared with a theoretical free-electron value of 23, and the low temperature value of gamma sub e is compared with values of 1.75 to 1.77 calculated from elastic constants. At room temperature gamma approximately gamma sub infinity is 2.00, so that gamma sub infinity-gamma sub 0 approximately 0.28, which agrees well with the theoretical estimates of Barron for a close-packed cubic lattice. Author