Chapter 6 - Oxide Fluorides of Rare Earth Elements

Abstract

The rare earths are the key elements in producing useful materials among which are alloys, intermetallics, and large numbers of nonmetallic compounds, such as oxides, chalcogenides, and halides. These materials have been widely used as functional substances with magnetic, optic, electro-optic, ferroelectric, super-electronic and -ionic conductive, nuclear properties, and so on. Almost all of these functional materials of the rare earths used practically are complex oxides with the structures of perovskite, garnet, pyrochlore, fluorite, and glass. Except for oxides, rare-earth fluorides have been utilized in the optical devices. These useful properties of the functional metal oxides originate from the partial covalency of the M–O bond and the variety of crystal structures. Recently, the binary rare-earth oxide fluorides, Ln2Ln'203F6, in which Ln and Ln' are different rare earths, have been reported to be applicable as an oxide ion-conducting solid electrolyte with much higher conductivity than that of stabilized zirconia.