2-CENTER MODEL FOR RADIATION-INDUCED ALUMINUM HOLE CENTER IN STISHOVITE

Electron spin resonance (ESR) has been measured for stishovite synthes ized under high pressure conditions from high purity SiO2 glass or nat ural quartz and irradiated by gamma-rays both at room temperature and at 77 K. The prominent signal detected at 77 K has anisotropic g-facto rs of orthorhombic symmetry, g(x) = 2.0155, g(y) = 2.0094 and g(z) = 2 .0033, and hyperfine sextets (I = 5/2) with A(x) = 0.394 mT, A(y) = 0. 372 mT and A(z) = 0.436 mT. The g-factors and the hyperfine structure indicate that this signal is due to a two-center type hole center, O-2 (3-), associated with an aluminum atom substituted at the silicon site in stishovite.