(TiO4)- in alpha -quartz studied by low-temperature electron paramagnetic resonance

Abstract

The centre (TiO4)-, formed by X-irradiation at 77 K in naturally occurring crystalline rose quartz, has been studied by single-crystal electron paramagnetic resonance (EPR) spectroscopy. Here the central 3d1Ti3+ ion exists within a slightly distorted oxygen tetrahedron. The hyperfine matrix of the low-abundance isotope 49Ti was measured at 8 K and the g matrix was measured at several temperatures from 30 K down to 4 K The analysis of be spin-population distribution within the centre showed that the unpaired spin is almost entirely in the Ti 3d orbital mod 3z2-r2). Estimates of the spin-lattice relaxation time T1 and of the EPR linewidth in be temperature range 4-30 K were also obtained. T1 decreases exponentially with increasing temperature, presumably owing to phonon coupling to the low-lying excited state mod xy) which is 8.1 meV (65 cm-1) above the ground state, via an Orbach process. At temperatures above approximately 15 K the abnormally large EPR linewidth is predominantly caused by lifetime broadening through T1. The near degeneracy of mod 3z2-r2) and mod xy) indicate that (TiO4)- has almost tetrahedral symmetry.