Rare-Earth Pnictide Oxides (RE,Ca) m Pn n O m (Pn = Sb, Bi): A Review of Crystal Structures, Chemistry, Compositions, and Physical Properties

Rare-earth-based pnictide oxides (RE,Ca) m Pn n O m (Pn = Sb, Bi) adopt a variety of interrelated structures based on specific stacking sequences of rare-earth oxide sublattices. These phases are all prepared via high temperature reactions and may be selectively produced in high purity. X-ray single crystal studies also revealed the disorder of pnictogen atoms in the non-charge balanced structures, which gives rise to unexpected physical properties. It is theorized that Anderson localization of the Pn p states results in an activation energy which forces semiconductor-type behavior in these phases. Interestingly, the extent of the localization of states is directly dependent on the magnitude of the disorder of the pnictogen atom, which also depends on pnictogen and/or the rare-earth atom that is used. By altering the composition of the sample with respect to the choice of Pn and/or RE, the physical properties of these select phases may be tuned to the desirable level without a change to the overall structure. The progression of this series of phases with respect to chemistry, structure, and physical properties is reviewed and discussed.