3 KINDS OF FRAMEWORK STRUCTURES OF CORNER-SHARING WO6 OCTAHEDRA DERIVED FROM PEROXO-POLYTUNGSTATES AS A PRECURSOR

Peroxo-polytungstic acid, formed by the direct reaction of metallic tungsten with hydrogen peroxide, precipitated an amorphous salt with various cations. Sintering those precursor salts at relatively low temperatures yielded crystalline complex oxides with the framework structures. These frameworks were based on six-membered rings of corner-sharing WO6 octahedra in common, but three distinct types occurred depending on the cation's size and valency: the hexagonal-WO3 type for K and Rb, the pyrochlore type for larger cations such as Cs and Tl, and another hexagonal type (a 2-D version of the pyrochlore type) for divalent cations such as Ba and Pb.