Absence of anomalous negative lattice-expansion for polycrystalline sample of Tb2Ti2O7

TL;DR

This study shows that polycrystalline Tb2Ti2O7 exhibits normal positive thermal expansion above 4 K, contrasting with previously reported negative expansion in single crystals below 20 K, highlighting differences in thermal behavior.

Contribution

It provides the first high-resolution diffraction evidence that polycrystalline Tb2Ti2O7 does not show anomalous negative thermal expansion, unlike single crystal samples.

Findings

Polycrystalline Tb2Ti2O7 exhibits positive thermal expansion above 4 K.

The crystal structure is confirmed as fully ordered cubic pyrochlore.

No negative thermal expansion observed in polycrystalline form.

Abstract

High resolution X-ray powder-diffraction experiments on a well-characterized polycrystalline sample of the spin liquid Tb2Ti2O7 reveal that it shows normal positive thermal-expansion above 4 K, which does not agree with the intriguing anomalous negative thermal-expansion due to a magneto-elastic coupling reported for a single crystal sample below 20 K. We also performed a Rietveld profile refinement of a powder-diffraction pattern taken at a room temperature, and confirmed that it is consistent with the fully ordered cubic pyrochlore structure.