Yttrium-89 magic angle spinning NMR study of rare-earth pyrochlores: paramagnetic shifts in the solid state

Abstract

{sup 89}Y MAS NMR spectra have been obtained from yttrium pyrochlores Y{sub 2-y}Ln{sub y}M{sub 2}O{sub 7} (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 {sup 89}Y 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, Y{sub 2}Sn{sub 2}O{sub 7} and Y{sub 2}Ti{sub 2}O{sub 7}, extra {sup 89}Y resonances were observed, due to the substitution of paramagnetic ions into the local coordination sphere surrounding an {sup 89}Y 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.