Self-trapping at aluminium-alkali centres in alpha -quartz

Abstract

We present a calculation of the self-trapping properties in alpha -quartz of aluminium-sodium centres using a Mott-Littleton calculation. It is found that the hole in (AlO4/M)0 with M=Na is most energetically favourable to self-trap at an oxygen atom nearest to the Al ion with a 'short' bond. It is also found that the Na ion is in the nearby c-axis channel on the long-bond side of the Al ion. These calculated results agree well with the experimental results. We also found that the hole is also energetically favourable to self-trap at an oxygen ion next nearest to the Al ion. The hole-trapping energies in the two cases are similar and therefore their sites may not be easily distinguished in the experiment.