The energetics of interaction between oxygen vacancies in sillimanite: A model for the mullite structure |
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| Authors: | S Padlewski V Heine G D Price |
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| Institution: | 1. Cavendish Laboratory, Madingley Road, CB3 OHE, Cambridge, UK
2. Department of Geological Sciences, University College London, Gower Street, WC1E 6BT, London, UK
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| Abstract: | A microscopic model is introduced to discuss the modulated structure of mullite. The oxygen vacancies of this aluminosilicate are known to play a central role. In particular, a single vacancy strongly orders its surrounding Al/Si tetrahedral sites. It is shown in this work that if two oxygen vacancies approach too closely to one another, their Al/Si  dressing overlap. This situation results in repulsive interaction. The field of interaction between the vacancies is estimated with the use of an atomistic computer simulation. We use a Bragg-Williams type of theory to dicuss the ordering pattern of the vacancies. Due to frustration between the two dominant repulsive interactions, our model predicts a modulated phase transition in agreement with observation. |
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