Cohesive Energies of Europium, Gadolinium, Holmium, and Erbium

A mass spectrometric method has been employed to study the solid-gas phase change in four rare-earth metals. The enthalpies of sublimation in kcal/M reducted to 298°K are: Eu, 43.11±0.25; Gd, 81.22±0.32; Ho, 75.04±0.44; and Er, 75.39±0.34. The corresponding cohesive energies in kcal/M as determined from presently available thermodynamic data are: Eu, 43.4; Gd, 81.9; Ho, 75.5; and Er, 75.7. A summary of the cohesion in the rare-earth series is included. A qualitative explanation of the unexpected variations is given in terms of the energetics of the metallic and gaseous states.