Ceramics-Silikáty 40, (4) 137 - 142 (1996) |
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QUALITATIVE MO TREATMENT OF THE γ-INDUCED PARAMAGNETIC CENTRES IN TITANIA BEARING SODIUM SILICATE GLASSES
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Pelikán Peter 1, Liška Marek 2
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1 Department of Physical Chemistry, Slovak Technical University,
Radlinského 9, 812 37 Bratislava, Slovak Republic
2 Institute of Inorganic Chemistry, Slovak Academy of Sciences,
M. Rázusa 10, 911 01 Trenčín, Slovak Republic
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The unusual behaviour of EPR spectra of γ-irradiated titania bearing sodium silicate glasses with various contents of titania
were qualitatively interpreted on the base of model molecular orbital calculations. As a model of the actual paramagnetic
particles were chosen the clusters which indemnify the reasonable compromise between the model of cluster and exactness of
calculation used. The results of the quantum chemical calculations show the preferential sensibilisation of Q² unit in comparison
with Q³ unit (the largest electron density in the vicinity of non bonding oxygens in Q² model). The bond strengths of Si-O bonds
in the neighbourhood of non-bridging oxygens show to the preferential substitution of Si⁴⁺ for Ti⁴⁺ in the vicinity of the boundary
of the cluster. The changes of the spin density distribution around the cluster after substitution of Si⁴⁺ for Ti⁴⁺ (the largest
delocalization) explain the unusual behaviour of the g-tensor component with titania content in the glasses.
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