Stuffed Rare Earth Pyrochlore Solid Solutions

TL;DR

This study synthesizes and characterizes a series of rare earth titanate pyrochlore solid solutions, revealing how lanthanide substitution influences crystal structure and magnetic interactions, opening new paths for exploring magnetic frustration.

Contribution

It introduces a new family of rare earth titanate pyrochlore solid solutions with tunable structures and magnetic properties, highlighting the effects of lanthanide substitution on disorder and magnetic frustration.

Findings

Lanthanide ions substitute mainly on Ti sites in some compositions.

Transition from pyrochlore to defect fluorite structure with increased lanthanide content.

Enhanced magnetic interactions due to added magnetic lanthanides.

Abstract

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 on X-ray powder diffraction data indicate that in Tb and Dy titanate pyrochlores, 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). In all of these Ln-Ti-O pyrochlores, the addition of magnetic Ln3+ in place of nonmagnetic 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.