SYNTHESES AND STRUCTURES OF THE NEW QUATERNARY GROUP-IV TELLURIDES CS0.68CUTITE4 AND CS3CUHF2TE10

The new compounds Cs0.68CuTiTe4 and Cs3CuHf2Te10 have been synthesized at 350 and 475 degrees C, respectively, through reaction of the eleme nts with a Cs2Ten flux. Cs0.68CuTiTe4 crystallizes in space group C-2h (3)-C2/m of the monoclinic system with four formula units in a cell of dimensions a = 19.728(11), b = 3.923(2), c = 13.374(7) Angstrom, beta = 129.65(1)degrees, V = 796.9(7) Angstrom(3) (T = 113 K). Cs3CuHf2Te1 0 crystallizes in space group C-i(1)-<P(1)over bar> of the triclinic s ystem with two formula units in a cell of dimensions a = 9.889(5), b = 10.916(6), c = 11.110(6) Angstrom, alpha = 92.08(1), beta = 90.15(1), gamma = 101.27(1)degrees, V = 1175.3(11) Angstrom 3 (T = 113 K). The structures of both compounds have been determined by single-crystal X- ray methods. Cs0.68CuTiTe4 has a three-dimensional channel structure. Cs+ cations occupy the channels. The channels are built up from layers that are interconnected by Te-Te bonds. In these layers there are pai rs of edge-shared CuTe4 tetrahedra that in turn edge-share to TiTe6 oc tahedra. The conductivity in the needle (b) direction is 5 x 10(-3) Om ega(-1)cm(-1) at room temperature. The structure of Cs3CuHf2Te10 compr ises infinite one-dimensional chains of HfTe7 polyhedra and edge-share d CuTe4 tetrahedra; these chains are separated from one another by Cs cations. A chain may be formulated as (1)(infinity)[CuHf2(Te-3)(Te-2) (3)(Te)(3-)]. The conductivity in the needle[11(1) over bar] direction is <1 x 10(-5) Omega(-1)cm(-1) at room temperature.