Stuffed rare earth pyrochlore solid solutions

Synthesis and crystal structures are described for the compounds Ln(2)(Ti(2-x)Ln(x))O(7-x/2), Where Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0 to 0.67. Rietveld refinements of X-ray powder diffraction data indicate that in the Tb and Dy titanate pyrochlores, the extra Ln(3+) cations mix mainly on the Ti(4+) site with little disorder on the original Ln(3+) site. For the smaller rare earths (Ho-Lu), stuffing additional lanthanide ions results in a pyrochlore to defect fluorite transition, where the Ln(3+) and Ti(4+) ions become completely randomized at the maximum (x = 0.67). Initial magnetic characterization for the fully stuffed x = 0.67 samples for Ln = Tb-Yb shows no long range ordering down to 2 K, and only partial saturation of the full expected magnetic moment under applied fields up to 5 T. In all of these Ln-Ti-O pyrochlores, the addition of magnetic Ln(3+) in place of non-magnetic Ti(4+) adds edge sharing tetrahedral spin interactions to a normally corner sharing tetrahedral network of spins. The increase in spin connectivity in this family of solid solutions represents a new avenue for investigating geometrical magnetic frustration in the rare earth titanate pyrochlores. (c) 2006 Elsevier Inc. All rights reserved.