Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique

TL;DR

This study reveals that single-crystalline Yb2Ti2O7 grown by the floating zone method is slightly 'stuffed' with Yb, affecting its magnetic properties, and suggests using lattice parameters to assess stoichiometry.

Contribution

It provides the first detailed structural analysis showing that floating zone-grown Yb2Ti2O7 crystals are subtly stuffed, impacting their magnetic behavior.

Findings

Single crystal Yb2Ti2O7 is 'stuffed' with Yb, with x=0.046(4).

Stuffing introduces disorder, affecting magnetic ground states.

Lattice parameter a can indicate stoichiometry in crystals.

Abstract

Recent neutron scattering and specific heat studies on the pyrochlore Yb2Ti2O7 have revealed variations in its magnetic behavior below 265mK. In the best samples, a sharp anomaly in the specific heat is observed at T=265mK. Other samples, especially single crystals, have broad features in the specific heat which vary in sharpness and temperature depending on the sample, indicating that the magnetic ground state may be qualitatively different in such samples. We performed detailed comparisons of the chemical structure of a pulverised single crystal of Yb2Ti2O7, grown by the floating zone technique, to a sintered powder sample of Yb2Ti2O7. Rietveld refinements of neutron powder diffraction data on these samples reveal that the crushed single crystal is best described as a "stuffed" pyrochlore, Yb2(Ti(2-x)Yb(x))O7-(x/2) with x = 0.046(4), despite perfectly stoichiometric starting material. Substituting magnetic Yb3+ on the non-magnetic Ti4+ sublattice would introduce random exchange bonds and local lattice deformations. These are expected to be the mechanism leading to of the variation of the delicate magnetic ground state of Yb2Ti2O7. Determination of the cubic cell length, a, could be useful as a method for characterizing the stoichiometry of non- pulverised single crystals at room temperature.