THE CALCIUM THALLATE CA3TL4O9, AN INTERGROWTH OF THE CATL2O4 AND CA2TL2O5 STRUCTURES, MEMBER N=1.5 OF THE SERIES CANTL2ON+3

A new calcium thallate Ca3Tl4O9 has been isolated. It crystallizes in a monoclinic cell, space group C2/m, with a = 11.118(3) Angstrom, b = 3.341(1) Angstrom, c = 12.287(3) Angstrom, and beta = 102.88(2)degrees . The ab initio determination of this structure shows that it consists of a regular intergrowth of the first two members of the calcium thal late family CanTl2O3+n:CaTl2O4 (n = 1) and Ca2Tl2O5 (n = 2). Intergrow th defects have been characterized by electron microscopy. Among all o xides and sulfides that belong to the lillianite family, Ca3Tl4O9 is t he only one that exhibits the (2,3)L structure, i.e., where layers are built up from ribbons of two and three edge-sharing octahedra alterna tely. (C) 1995 Academic Press, Inc.