Effect of lanthanides on the relaxation rates of 89Y and 29Si in yttrium silicon oxynitride phases.

Additions of paramagnetic lanthanides are found to increase the relaxation rates of both 89Y and 29Si in the yttrium silicon oxynitride compounds Y2Si3N4O3 (N-melilite) and Y4Si2O7N2 (J-phase), allowing the observation of previously unreported 89Y magic-angle spinning nuclear magnetic resonance spectra of these phases. The dependence of the 89Y and 29Si relaxation rates was determined as a function of Yb3+ and Gd3+ concentration. Both the 29Si and 89Y resonances become broader with increasing Yb concentration, but at all lanthanide concentrations the 89Y spectrum of J-phase is broader than that of N-melilite, possibly due to a greater distribution of Y site geometries in the former. At concentrations below about 360 mumol g-1, the lanthanide ions appear to be incorporated in the lattice, but are not involved in covalent bonding to Y or Si. The effect of a series of lanthanides on the 89Y and 29Si relaxation rates and line widths is presented in terms of the lanthanide spin quantum numbers and magnetic moments. The most effective lanthanide was found to be Eu3+, giving fast relaxation (particularly for 89Y) and sharp lines.