Y-89 MAS NMR-STUDY OF RARE-EARTH PYROCHLORES - PARAMAGNETIC SHIFTS IN THE SOLID-STATE

89Y MAS NMR spectra have been obtained from yttrium pyrochlores Y2-yLnyM2O7 (Ln = Ce, Pr, Nd, Sm, Eu, Yb; M = Sn, Ti). Incorporation of the paramagnetic ions into the diamagnetic compounds was found to cause large reductions in the 89Y nuclear relaxation times enabling spectra to be accumulated in relatively short times in comparison to similar diamagnetic systems. In addition to the resonances of the diamagnetic end-member compounds, Y2Sn2O7 and Y2Ti2O7, extra 89Y resonances were observed, due to the substitution of paramagnetic ions into the local coordination sphere surrounding an 89Y nucleus. The paramagnetic shifts were found to be proportional to the number of lanthanide ions substituted for yttrium in the first coordination sphere; the intensities of the resonances could be used to determine the concentration of paramagnetic rare-earth ions in the diamagnetic phase. The direction and magnitude of the shifts induced by the presence of paramagnetic ions suggest that there could be a significant contribution from a dipolar mechanism. © 1990, American Chemical Society. All rights reserved.