Syntheses, crystal structures, and band gaps of Cs2Cd3Te4 and Rb2Cd3Te4

Single crystals of Cs2Cd3Te4 grow as yellow plates from the reaction of Cs2 Te3 with Cd and Te at 873 K; orange plates of Rb2Cd3Te4 grow from the react ion of Rb2Te3 with Cd and Te at 773 K. The structures of both compounds hav e been determined from single crystal X-ray diffraction data. Cs2Cd3Te4 cry stallizes in the orthorhombic space group Ibam with unit cell parameters a = 6.667(1) Angstrom, b = 13.010(3) Angstrom, c = 15.390(3) Angstrom, Z = 4, T = 113 K. Rb2Cd3Te4 crystallizes in the monoclinic space group C2/c with unit cell parameters a = 14.424(2) Angstrom, b = 15.350(2) Angstrom, c = 12 .864(2) Angstrom, beta = 116.249(2), Z = 8, T = 153 K. Both structures comp rise layers of edge-shared CdTe4 tetrahedra separated by alkali metal catio ns; however, the connectivity of the CdTe4 tetrahedra and the stacking of t he layers are different in each compound. Bandgaps of 2.48 eV for Cs2Cd3Te4 and 2.30 eV for Rb2Cd3Te4 were determined from UV/Vis diffuse reflectance measurements made at 20 degrees C. (C) 2000 Elsevier Science S.A. All right s reserved.