THE EPR SPECTRAL PARAMETERS AND DYNAMIC PROPERTIES OF THE CENTER [TIO4 NA]A0 IN X-IRRADIATED ALPHA-QUARTZ

The centre [TiO4/Na]A0 in crystalline quartz has been studied in detail by single-crystal electron paramagnetic resonance (EPR) spectroscopy. The hyperfine and nuclear quadrupole matrices of Na-23 and the hyperfine matrices of the low-abundance isotope Ti-49 have been measured at both 35 and 70 K. At 35 K the titanium defects exhibit C1 symmetry, while C2 symmetry was observed above ca 60 K. At all temperatures the Na+ ion has an equal probability of being located in one of two regions, off the two-fold axis that passes through the silicon position occupied by the Ti3+ ion. Above ca 60 K, the rate (measured at 9.95 GHz) of transfer for the sodium ion between the two regions is sufficiently great that its (time-averaged) position appears to be on the two-fold axis. An activation energy of 3.3 +/- 0.2 kJ mol-1 was measured for the motional process within the defect cluster.