Synthetic Strategies for New Inorganic Oxide Flourides and Oxide Sulfates

The low temperature fluorination of low dimensional mixed metal oxides can be achieved in a variety of ways to provide new structures and modified electronic characteristics. The potential of these methods for the synthesis of new materials is considered, with particular reference to the fields of copper oxide superconductors and layered manganese oxide colossal magnetoresistance (CMR) phases; in both areas, careful structural and electronic control is necessary for optimised properties. The fluorination mechanisms are quite complex, and this paper describes the synthesis of three new oxide fluorides: La_1.9Sr_1.1Cu₂O₅F₂, PbSr₂YCU₃O₆F₄ and La_1.2Sr_1.8Mn₂O₇F₂, via processes which involve anion insertion, anion substitution and cation extraction. The use of a related strategy to incorporate more complex anions into oxides is also discussed, and the assimilation of SO₄^2- ions into Bi₂O₃ to give phases of composition Bi₂O(3-x)(SO₄)(x) is described.