HTB-LIKE 6-MEMBERED RINGS OF OCTAHEDRA IN SOME NEW OXIDES - STRUCTURAL ASPECTS AND RELATED PROPERTIES

The HTB-like six-membered ring of octahedra is the common building unit of all compounds presented in this review. In three of them the entire (001) HTB plane is observed, associated to either XO4, X2O7, or X3O9 groups (X=P, Si, Ge). This association can result in a 2D network as in K3Sb3P2O14, xH2O, as well as in a condensation of similar layers leading to the 3D framework observed in Cs3Sb3Ge2O13. The 3D framework of Cs8Nb10O23□(Si3O9)2 appears as the first term of an intergrowth between the pyrochlore and benitoite structural types. These compounds are good ion-exchangers or promising precursors for such materials. Another family of compounds containing HTB-like six-membered rings corresponds to the first term of an intergrowth between HTB and perovskite types. Their physical properties are discussed in relation with the nature of the cations located either in the framework octahedra or in the perovskite and HTB sites. © 1992 Academic Press, Inc.