Structural and Trapping Characteristics of a New Al Defect in Vitreous Silica

Abstract

I have found with EPR that some Al impurity atoms in type-I and -II vitreous silica are bonded to only three oxygen atoms. Under ionizing radiation at 4 K, diamagnetic Al${\mathrm{O}}_3$ traps an electron and becomes paramagnetic Al${\mathrm{O}}_3^{-}$; this charge configuration is observed with EPR for $T\lesssim 330$ K. With an alkali compensator Al${\mathrm{O}}_3^{-}$ exists for $T\lesssim 550$ K, but if the compensator involves hydrogen, the extra electron can remain trapped for $T\lesssim 650$ K.