10 K electron paramagnetic resonance of a d1 Ti3+ centre in X-irradiated zircon (zirconium silicate)

A d1 Ti3+ centre formed by X-irradiation of a synthetic zircon single crystal at 77 K has been studied by electron paramagnetic resonance (EPR) at 10 K. The Ti3+ ion occupies a substitutional site of point group symmetry 42m (D2d). Absence of both site splitting in general crystal orientations and of superhyperfine structure from a +1 ion indicated that a nearby charge compensator was not involved. Comparison with EPR measurements on Ti3+/ α quartz centres, point charge calculations and 29Si hyperfine splittings indicated that the Ti3+ centre results from electron capture by Ti4+ occupying a Zr4+ site in the crystal; the designation (TiO8)s suggested. Precise spin-Hamiltonian parameters, including 47Ti (I=5/2, 7.4%) and 49Ti (I=7/2, 5.4%) hyperfine, nuclear electric quadrupole and nuclear Zeeman parameter matrices, together with high-spin nuclear terms of dimension I4, I3S, I5S, BI3 and BI5 were determined. The set of terms BI, BI3 and BI5 were found to be crucial in obtaining a good fit to the many 'forbidden' hyperfine lines observed. This resulted in determination of nuclear quadrupole and nuclear Zeeman parameters with precision not hitherto attained in conventional single-crystal EPR measurements. (authors)