A. Mirgorodsky

Raman spectra of tetragonal zirconia: powder to zircaloy oxide frequency shift

Abstract The shifts of the two main characteristic Raman active bands of t-ZrO2 in oxide films developed on zirconium alloy relatively to their position in nanopowder (267, 456 cm −1 ) are discussed. The origin of the shifts is analyzed within the lattice dynamical treatment according to which neither hydrostatic compression nor biaxial one can be responsible for this shift. It is put in evidence that only an abnormal high value of the internal tetragonality (Δz=Lz/c) can provide this effect. Additionally, the symmetry assignment of the two bands are determined which, in particular, argues for the identification of the band near 267 cm −1 as a totally symmetric A1g soft mode.

On the condensation mechanism of the dioxides of sixth-group elements: an ab initio approach

A quantum mechanical ab initio simulation of XO2 molecules (X = O, S, Se, Te and Po) and the relevant dimers has been performed. The X–O bond polarity and the bent configuration of the XO2 species are discussed as factors governing their condensation mechanisms. Three points are emphasized: (i) the fundamental difference between the constitution of the condensed phases of OO2 and SO2, on the one hand, and those of SeO2 and TeO2, on the other; (ii) the occurrence of polymorphism in crystalline TeO2 and its absence in crystalline SeO2; (iii) the driving forces of the γ–α polymorph transformation in crystalline TeO2.

Third order nonlinear optical properties of a paratellurite single crystal

The (a,b) plane angular dependence of the third-order nonlinear optical susceptibility, χ(3), of a c-cut paratellurite (α-TeO2) single crystal was quantitatively evaluated here by the Z-scan technique, using a Ti:sapphire femtosecond laser operated at 800 nm. In particular, the mean value Re( ⟨χ(3)⟩a,b)(α-TeO2) of the optical tensor has been extracted from such experiments via a direct comparison with the data collected for a fused silica reference glass plate. A Re(⟨χ(3)⟩(a,b)(α−TeO2)):Re(χ(3))(SiO2 glass) ratio roughly equal to 49.1 is found, and our result compares thus very favourably with the unique experimental value (a ratio of ∼50) reported by Kim et al. [J. Am. Ceram. Soc. 76, 2486 (1993)] for a pure TeO2 glass. In addition, it is shown that the angular dependence of the phase modulation within the (a,b) plane can be fully understood in the light of the strong dextro-rotatory power known for TeO2 materials. Taking into account the optical activity, some analytical model serving to estimate the di...