The Atomic Heats of Lithium, Sodium and Potassium between 1.5 and 20 K

Abstract

The atomic heats of lithium, sodium and potassium have been measured between 1.5° and 20°K, chiefly with the object of determining the effective mass of the conduction electrons. For lithium it was found that, below 4°K, the atomic heat could be written as C=(0.418T+0.0092T3) × 10-3 cal mol-1 deg-1, corresponding to an effective mass m* for the conduction electrons of 2.32 times the free electron mass m0, and a Debye characteristic temperature Θ for the lattice of 369°K. Near 15°K a small anomaly in the atomic heat was observed. For sodium below 4.5°K the atomic heat was of the form C=(0.328T + 0.117T3) × 10-3 cal mol-1 deg-1, corresponding to m* = 1.22m0 and Θ = 158°K, and no anomalies were found. For potassium it was not possible to analyse the atomic heat so exactly, but a value of m* of about 1.1m0 is estimated, with Θ=89°K. Smoothed values of the atomic heats are tabulated at intervals up to 20°K, and calculated values of Θ are given graphically. The internal energy, entropy and free energy are also tabulated.