Abstract

The rare earth metals form the largest subset of the AB₂ Laves phase compounds. The rare earth element (R) is always the larger A metal, and they form Laves phases with most of the Group 7–10 elements, plus Mg and Al. As with all Laves phases, the rare earth RB₂ compounds conform with the size rule which had been established in the mid 1930s. Electron concentration effects have also been observed in the RB₂ phases. A number of anomalies and unusual behaviors have been discovered over the years: the La deficiency in “LaNi₂” and of R in other “RNi₂” Laves phase compounds; the crystal structure sequence in the RMn₂ compound series; the relationship between the Debye temperature and the radius ratio; the Ce valence in the CeB₂ compounds; and the thermodynamic nature of the magnetic transition in the RCo₂ phases.