Phase Diagrams of Binary Systems Formed by Rare Earth Trifluorides

Abstract

The present paper is a follow-up on an earlier investigation [1–4] of phase diagrams of a large group of RF₃-R’F₃ systems where R denotes rare earth elements. In recent years single crystals of single- or multicomponent fluorides with structure belonging to tysonite (LaF₃) and rhombic yttrium fluoride (YF₃) types became attractive as laser materials [5, 6], infra-red-to-visible light converters [7], and ionic conductors with high fluorine-ion conductivity [8, 9]. Detailed knowledge of the phase diagrams of the respective systems is necessary for successfully growing crystals of rare earth fluorides and for activating them with lanthanide ions. The polymorphism and morphotropic alternation of structure types in the sequence of rare earth trifluorides [10] limit the possibility of growing single-component matrices with particular structures. These restrictions are partially removed by going to more complex compositions [3]. We have analyzed phase diagrams of RF₃-R’F₃ systems and mutual isomorphous substitutions of rare earth ions in tysonite, rhombic, and hexagonal yttrium fluoride structural types in order to accumulate additional information on the possibility of growing multicomponent materials.