The magnetic properties of the oxygen–hole aluminum centers in crystalline SiO2. III. [AlO4]+

Abstract

The EPR spectra of [AlO4]+ have been measured in α-quartz at ca. 35 K after X-irradiation at 77 K. This center is believed to contain two electron holes, one at each of two symmetry-related oxygen ions bonded to an aluminum ion substituted for silicon, forming a triplet spin system. Measurements of the two primary 27Al hyperfine multiplets (Ms = 0 ↔ Ms = ± 1) as well as the quasi-forbidden multiplet (Ms = + 1 ↔ Ms = −1) at half field have been made, and have led to a spin-Hamiltonian (matrices [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]). A crystal two-fold axis contains the aluminum ion and relates the two-hole-bearing oxygen ions, as well as the two outer silicon ions bonded respectively to the latter. The electronic quadrupole matrix [Formula: see text] is attributed primarily to the magnetic dipole–dipole interaction between the two unpaired electrons. The results of a comparison among the matrices [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and the corresponding matrices for the related single-hole centers [AlO4]0 and [AlO4/M+]+ (where M = H, Li) are consistent with the model for [AlO4]+.