La4(Si5.2Ge2.8O18)(TeO3)4 and La2(Si6O13)(TeO3)2:: Intergrowth of the lanthanum(III) tellurite layer with the XO4 (X = Si/Ge) tetrahedral layer

Two novel lanthanum(III) silicate tellurites, namely, La-4(Si5.2Ge2.8O18)(TeO3)(4) and La-2(Si6O13)(TeO3)(2), have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La-4(Si5.2Ge2.8O18)(TeO3)(4) features a three-dimensional (3D) network composed of the [(Ge2.92Si5.18)O-18](4-) tetrahedral layers and the [La-4(TeO3)(4)](4+) layers that alternate along the b-axis. The germanate-silicate layer consists of corner-sharing XO4 (X = Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La-2(Si6O13)(TeO3)(2) is a 3D network composed of the [Si6O13](2-) double layers and the [La-2(TeO3)(2)](2+) layers that alternate along the a-axis. The [Si6O13](2-) double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and La3+ eight-member rings. The TeO32- anions in both compounds are only involved in the coordination with La3+ ions to form a lanthanum(III) tellurite layer. La-4(Si5.2Ge2.8O18)(TeO3)(4) is a wide band-gap semiconductor. (c) 2007 Elsevier Inc. All rights reserved.