Stuffed rare earth pyrochlore solid solutions

Abstract

Synthesis and crystal structures are described for the compounds Ln 2(Ti 2− xLn 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.