A.P. Mirgorodsky

Dynamics and structure of TeO2 polymorphs: model treatment of paratellurite and tellurite; Raman scattering evidence for new γ- and δ-phases

Abstract The joint lattice-dynamical model study of the vibrational and elastic properties of paratellurite (α-TeO2) and tellurite (β-TeO2) has been conducted. Emphasis was laid on the crystal chemistry aspects of Raman spectra of these lattices. Results were used to interpret the Raman spectra of two new polymorphs (γ and δ) of tellurium dioxide, and to clarify their relationships with the spectrum of pure TeO2 glass.

Crystal structure, Raman spectrum and lattice dynamics of a new metastable form of tellurium dioxide: γ-TeO2

Abstract The crystal structure of a new metastable form of tellurium dioxide, γ-TeO2 (orthorhombic, P212121 (no. 18); a=4.898 A , b=8.576 A , c=4.351 A ; Z=4) was solved ab initio and refined to RB=0.0387 and Rp=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 α-TeO2 one. There exist two different kinds of Te–O–Te bridges in γ-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 γ-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 γ-phase are discussed.

Dynamics and crystal chemistry of tellurites: 1. Raman spectra of thallium tellurites: Tl2TeO3, Tl2Te2O5 and Tl2Te3O7

Abstract Raman spectra of the three entitled crystals are analysed within the framework of a lattice-dynamical model treatment using preliminary obtained X-ray diffraction data. The short range atomic arrangement and spectrochemical peculiarities of these structures are jointly discussed, which is considered as an initial step for studying the nature of the glass phases in the x Tl 2 O+(1− x )TeO 2 system. The charged TeO 3 2− groups and the neutral TeO 2 quasi-molecules are proposed as the basic units forming the complex tellurite anions. However, no relevant characteristic frequencies can be indicated in the spectra since the interatomic separation in those units are highly variables and their vibrational states are mixed and delocalised.

Glass formation study within the TeO2-TlF and Tl2Te3O7-TlF systems

Abstract Large glassy domains have been observed at 800xa0°C within the TeO 2 –TlF (from 7 to 65xa0mol% of TlF) and Tl 2 Te 3 O 7 –TlF (from 0 to 75xa0mol% of TlF content) systems. The density, glass transition and crystallisation temperatures of glassy samples have been determined. The main features of a structural evolution within the TlF–TeO 2 glasses have been interpreted by analysing the relevant Raman spectra, and comparing them with those previously observed for the Tl 2 O-TeO 2 system.