Calorimetry below 1 K: The specific heat of copper

Abstract

A technique is described which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat switch. As a test of this technique the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04–1 K. The presence of hydrogen increases the specific heat by ≈ 1% as has been reported previously at higher temperatures. Above 0.3 K the data for hydrogen-free copper are in good agreement with the copper reference equation. At lower temperatures there is an additional contribution to the heat capacity which may be associated with oxygen impurities.

Low-temperature specific heat, thermal conductivity, and ultrasonic velocity of glassy carbons

“…Specific heat measurements were made using a technique described previously. 6 The data are presented in Fig. 2.…”

The specific heat of copper at temperatures below 0.2 K

“…The impurity content of this sample is listed in Table I with similar information for the samples ~ used in Ref. 4. The rod from which our sample was cut had apparently been cast in air, as it contained small, spherical voids.…”

“…The oxygen content of the material used in Ref. 4 was -1 ppm in the bulk, or -10 ppm if the surface oxidation was not removed prior to analysis. The hydrogen content of the present sample was -1 ppm atomic.…”

“…4 The sample was thermally connected to the refrigerator via a small copper wire of electrical-grade purity having a total mass of ---0.06 g. The sample was mechanically supported at three points, using, for thermal isolation at each point, several layers of dry Mylar 5 • 10 -3 cm thick. The heater was a thin film of Cu-Ni alloy; the thermometer was a carbon chip calibrated in each run against germanium thermometers.…”

“…This fact was recognized in Ref. 4, and it was there suggested that oxygen might in some way be responsible. However, the reduction in AC caused by oxygen anneal would appear to rule this out.…”