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 ${\mathrm{SiO}}_2$ α quartz; these features are shown to derive from the formation of the Al-O chemical bond. The dangling bond in the [Al(${\mathrm{O}}_4$ ${)}_{1/2}$ ${]}^{\mathrm{-}}$ 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., ${\mathrm{Li}}^{+}$, ${\mathrm{H}}^{+}$), trapped in an optical channel of the defective quartz has been determined as a function of its location with respect to the aluminum position. © 1996 The American Physical Society.