Stuffed rare earth pyrochlore solid solutions

Synthesis and crystal structures are described for the compounds Ln2(Ti2−xLnx)O7−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 Ln3+ cations mix mainly on the Ti4+ site with little disorder on the original Ln3+ site. For the smaller rare earths (Ho–Lu), stuffing additional lanthanide ions results in a pyrochlore to defect fluorite transition, where the Ln3+ and Ti4+ 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 Ln3+ in place of non-magnetic Ti4+ 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.

A simplified model of the transition from pyrochlore to fluorite in the series Ln2(Ti2−xLnx)O7−x/2 (Ln=Tb–Lu, 0⩽x⩽0.67), with Ho as an example. The separate corner sharing tetrahedral lattices of cations in the pyrochlore structure develop into edge sharing tetrahedra as extra Ln is stuffed in place of Ti. The increased spin connectivity in these new materials represents a new avenue of study in the well-known rare earth titanate pyrochlores in view of geometrical magnetic frustration.Figure optionsDownload as PowerPoint slide