Discoveries in real crystals of rare earth metal compounds by electron microscopy - Lamellar intergrowth and domains of phasoids

Condensed cluster phases with the nominal compositions Ln(14)(C(2))(3)I(20) (Ln = La, Ce, Pr) are strongly disordered by a lamellar intergrowth. The thickness and composition of layers of clusters containing n (C(2))Ln(6) octahedra linked via opposite edges is determined by n. The disorder is characterized by variations of n as well as by variations of the thickness of lamellae containing only one kind of cluster. As a rule, the crystals are built from straight lamellae with constant n, however, large variations of n were occasionally observed giving rise to bending and truncation of the lamellae inside compact crystals. The power of electron microscopy techniques for the characterization of such phasoid-type real crystals is demonstrated and the structure of the new compound Pr(14)(C(2))(3)I(20) is presented. (C) 2007 Elsevier Masson SAS. All rights reserved.