Valence, coordination number, and PAV cells in metallic rare earth compounds

Abstract. — Polyhedral atomic volumes, Voronoi volumes, generalized coordination numbers, and Pauling's metallic valences are given for 24 intermetallic rare earth compounds. The results clearly indicate that as much as 33 % rare earth isovalent volume contraction can occur upon compound formation while the atomic volumes of aluminum and the transition elements are nearly constant. Earlier discussions of bond formation in rare earth compounds [1-5] using Pauling's metallic radii [6] and the bidirectional orbital approximation [7] have strongly suggested that the effective radius of the rare earth atoms is surprisingly variable and may even be anisotropic in some SmCo5-type [4] and Laves phase [5] compounds. The power of these methods, i.e. Pauling's metallic radii (PMR) and the bidirec-tional orbital approximation (BOA), combined with the concept of the Voronoi cell [8], is indicated not only by the prediction [4] of the unstability of th