The Atomic Heats of Calcium, Strontium and Barium between 1.5 and 20 K

The atomic heats of calcium, strontium and barium have been measured in the temperature range 1.5° to 20°K, with the primary object of obtaining values for the electronic contributions to the specific heats. In all three metals at the lowest temperatures an atomic heat of the form C = AT + 1943( T /Θ) 3 joule deg -1 (g atom) -1 is found, where A and Θ are respectively (2.73 ± 0.06) × 10 -3 and 228.9 ± 1.7°K for calcium, (3.64 ± 0.18) × 10 -3 and 147.0 ± 1.2°K for strontium and (2.7 ± 0.5) × 10 -3 and 110.5 ± 1.8°K for barium. The experimental values of A , which represent the electronic contribution to the atomic heat, are compared with those calculated on the basis of the Sommerfeld free-electron model, and are found to be between 1.4 and 2.0 times as great, indicating a considerable overlapping of the first two Brillouin zones. Smoothed values of the atomic heats are tabulated at intervals up to 20°K and the variations of Θ with temperature are shown graphically. The internal energies, entropies and free energies are also tabulated.