Abstract
The centre [TiO 4/Na] A 0 in crystalline quartz has been studied in detail by single-crystal electron paramagnetic resonance (EPR) spectroscopy. The hyperfine and nuclear quadrupole matrices of 23Na and the hyperfine matrices of the low-abundance isotope 49Ti have been measured at both 35 and 70 K. At 35 K the titanium defects exhibit C 1 symmetry, while C 2 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 Ti 3+ 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.
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