All-electron study of the electronic properties of quartz with Al substitutional impurity

An aluminum defect in quartz has been studied by means of all-electron calculations based on the full-potential linearized-augmented-plane-wave method. A comparative study of alumina, pure quartz, and Al-substituted quartz shows that the Al impurity introduces levels between the bonding and nonbonding states of pure SiO2 alpha quartz; these features are shown to derive from the formation of the Al-O chemical bond. The dangling bond in the [Al(O-4)(1/2)](-) unit is evenly shared among the four oxygen atoms adjacent to the defect, and no bias of the charge density around the impurity is observed. A planar averaged potential energy curve for a light carrier ion (e.g., Li+, H+), trapped in an optical channel of the defective quartz has been determined as a function of its location with respect to the aluminum position.