Determination of the origin and magnitude of Al/Si ordering enthalpy in framework aluminosilicates from ab initio calculations |
| |
| Authors: | J D C McConnell A De Vita S D Kenny V Heine |
| |
| Institution: | (1) Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK, GB;(2) Institute Romand de Recherche Numérique en Physique des Matériaux, IN-Ecublens, CH-1015 Lausanne, Switzerland, CH;(3) Cavendish Laboratory (TCM), University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK, GB |
| |
| Abstract: | Ab initio total energy calculations based on a new optimised oxygen pseudopotential has been used to determine the enthalpy
of disorder for the exchange of Al and Si in tetrahedral coordination in simple derivative aluminosilicate structures based
on the high temperature tridymite structure. The problem has been studied as a function of defect interaction, and defect
concentration, and the results indicate that the energy for Al/Al neighbouring tetrahedra can be assigned primarily to two
effects, the first, a coulombic effect, associated with the disturbed charge distribution, and the second associated with
the strain related to misfit due to the very different dimensions of the Si and Al containing tetrahedra. In practice each
of these effects contributes approximately 0.2 eV per Al−Al neighbour to the overal disorder enthalpy. These simple results
were obtained after a careful study of possible chemical interaction between adjacent Al/Si containing tetrahedra which showed
that chemical interaction was effectively absent. Since individual Al/Si tetrahedra proved to be discrete entities that are
individually heavily screened by the shared oxygens it follows that coulombic and strain effects in disorder effectively account
for the whole of the disorder enthalpy. The complete set of results have been used to establish new criteria for the structure
and disorder enthalpies of the feldspar group of minerals and their long period derivatives.
Received: October 7, 1996 / Revised, accepted: March 17, 1997 |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
