Crystal structure, Raman spectrum and lattice dynamics of a new metastableform of tellurium dioxide: gamma-TeO2

The crystal structure of a new metastable form of tellurium dioxide, gamma- TeO2 (orthorhombic, P2(1)2(1)2(1) (no. 18); fl = 4.898 Angstrom, b = 8.575 Angstrom. c = 4.351 Angstrom; Z = 4) was solved ab initio and refined to R- B = 0.0387 and R-P = 0.115, On the basis of a Rietveld analysis of its powd er X-ray diffraction pattern. Each Te atom is coordinated to four oxygen at oms, and its coordination polyhedron has a view of distorted trigonal bipyr amid (disphenoid) TeO4E with one equatorial corner occupied by lone pair E. These units frame a three-dimensional network of the same type as the alph a-TeO2 one. There exist two different kinds of Te-O-Te bridges in gamma-TeO 2: one of them is nearly symmetric, and the other is highly asymmetric. The former bridges constitute polymeric chains along the: Oz-axis. Such a characterization of the gamma-TeO2 structure is supported by the ana lysis of the Raman spectra using the lattice dynamical model treatment in w hich the lattice vibrations are considered jointly with the elastic propert ies. All the longwave frequencies and the elastic constants were thus estim ated. Possible relations between the structure of the TeO2 glass and the ga mma-phase are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved .