An EPR/ENDOR investigation of a [ZrPO4]0 centre in x-irradiated zircon:: the Zr(α) centre

The Zr(alpha) centre is the most prominent centre observed after low temperature x-irradiation of zirconium silicate (zircon). The centre has been identified as due to an electron trap in the form of a Zr3+ ion in the zircon lattice with the centre being stabilized by interaction with a 100% abundant I = 1/2 ion. Previous reports have discussed the Zr(alpha) centre in terms of an Y-89(3+) (I = 1/2) ion in a neighbouring Zr4+ site. Using both EPR and ENDOR it has now been possible to show unequivocally that the I = 1/2 nuclear interaction is due to the presence of a P-31 ion. Detailed analysis of the g and hyperfine matrices for Zr-91, P-31 and Si-29 is used to develop a model of the centre as an electron trapped on zirconium as a Zr3+ ion with a P5+ ion in the nearest Si4+ site on the mirror plane. The defect is now best described asa [ZrPO4](0) centre.