Ab initio Calculations of NMR Parameters of Highly Coordinated Oxygen Sites in Aluminosilicates.

Abstract

Ab initio calculations have been carried out for the three polymorphs of SiAl2O5 in order to study the 17O NMR characteristics of tricoordinated O atoms, O[3], and tetracoordinated O atoms, O[4], that are possibly present in the structure of aluminosilicate glasses. We present δiso, CQ, and η calculations using the density functional theory-based GIPAW method for all silicon, aluminum, and oxygen sites and in particular for the 14 O[3] atoms, which are bonded to three Al or Si atoms in the andalusite, sillimanite, and kyanite polymorphs of SiAl2O5. The O[4] parameters calculated in kyanite are also compared with the corresponding site in α-Al2O3. The calculated values for the 29Si and 27Al isotropic chemical shift values as well as 27Al quadrupolar coupling constants (CQ) and asymmetry parameters (η) are in good agreement with experimental data. Apart from in alumina and in grossite CaAl4O7, 17O NMR parameters have not been measured experimentally yet but the CQ and η values obtained for all sites are con...