Order-disorder (OD) structures of Rb2Zn(TeO3)(CO3)·H2O and Na2Zn2Te4O11

Abstract

Abstract Single crystals of the two alkali metal zinc oxidotellurates(IV), Rb2Zn(TeO3)(CO3)·H2O and Na2Zn2Te4O11, were obtained by reactions of mixtures of ZnO, TeO2, Rb2CO3 (molar ratios 2:3:6) and ZnO, TeO2, Na2CO3 (molar ratios 2:3:10), respectively, with small amounts of water as a mineralizer. Both compounds crystallize as order-disorder (OD) structures of layers and feature a high stacking fault probability. The crystal structure of Rb2Zn(TeO3)(CO3)·H2O is composed of layers extending parallel to (100). The structure is composed of two kinds of non-polar OD layers consisting of trigonal-pyramidal [TeO3]2−, tetrahedral [ZnO4]6−, Rb1+, and CO3 2−, H2O, Rb2+, respectively. Different centrings of the layer groups lead to an ambiguity in the stacking arrangement. The crystal structure of Na2Zn2Te4O11 is built from layers extending parallel to (001). Trigonal-pyramidal [TeO3]2− and bisphenoidal [TeO4]4− polyhedra form [Te4O11]6− groups, which are connected by longer Te–O-contacts to form 1 ∞[Te8O22]12− double chains oriented along either [100] or [010]. These chains form non-polar layers, which appear alternatingly in two orientations related by a fourfold rotoinversion. The Zn2+ and Na+ cations are located at the layer interface. The stacking ambiguity is due to different lattices of adjacent layers.