STRUCTURE AND CHARACTERIZATION OF A MIXED-CRYSTAL RB2SO4.TE(OH)(6)

Rb2SO4.Te(OH)(6) mixed crystals (RTMC) crystallizes in the monoclinic system with space group P2(1)/a and cell parameters: a=11.454(5) Angst rom, b=6.658(4) Angstrom, c = 13.636(4) Angstrom, beta = 107.08 degree s(2), V=994.03(4) Angstrom(3), Z=4, D-x=2.918 g cm(-3). F(0 0 0)=912, T=298(2) K (room temperature phase), R=0.036 and WR=0.0860 for 1278 ob served reflections. The significance of this structure is the presence of both SO42- and TeO66- anions in the same crystal. Differential sca nning calorimetry traces show three anomalies at about 414 K, 424 K an d 495 K characterizing the three phase transitions in this material. R aman and IR spectra of Rb2SO4.Te(OH)(6) mixed crystals (RTMC) recorded at room temperature in the frequency range 10-4000 cm(-1), show that the two different anions SO42- and TeO66- coexist in the crystal indep endently. The bands are in agreement with the monoclinic room temperat ure phase. (C) 1998 Elsevier Science S.A. All rights reserved.