Crystal structure, Raman spectrum and lattice dynamics of a new metastable form of tellurium dioxide:: γ-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 powder X-ray diffraction pattern. Each Te atom is coordinated to four oxygen atoms, and its coordination polyhedron has a view of distorted trigonal bipyramid (disphenoid) TeO4E with one equatorial corner occupied by lone pair E. These units frame a three-dimensional network of the same type as the alpha-TeO2 one. There exist two different kinds of Te-O-Te bridges in gamma-TeO2: 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 analysis of the Raman spectra using the lattice dynamical model treatment in which the lattice vibrations are considered jointly with the elastic properties. All the longwave frequencies and the elastic constants were thus estimated. Possible relations between the structure of the TeO2 glass and the gamma-phase are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.