Synthesis, crystal growth and characterization of the pyrochlore Er2Ti2O7

TL;DR

This study investigates how synthesis and growth conditions affect the composition, structure, and magnetic transition temperature of Er2Ti2O7 pyrochlore, highlighting the importance of stoichiometry for its magnetic properties.

Contribution

It demonstrates improved crystal growth techniques for stoichiometric Er2Ti2O7 and links stoichiometry to magnetic transition behavior.

Findings

Lattice parameters vary with Ti deficiency or excess.

Stoichiometric crystals show a magnetic transition at ~1.23K.

Growth method influences crystal quality and stoichiometry.

Abstract

Pyrochlore erbium titanate samples in the form of powders (with nominal compositions of Er2Ti2+xO7) and bulk single crystals were prepared to elucidate the effect of synthesis and growth conditions on their composition, structure, and transition temperature. All samples were characterized using X-ray diffraction and specific heat measurements. Larger lattice parameters were measured for the Ti-deficient stuffed powders, Er2(Ti2-xErx)O7-{\delta}, while Ti-rich anti-stuffed powders, (Er2-xTix)Ti2O7+{\delta}, showed a decrease in lattice parameter. The lattice parameter for the stoichiometrically synthesized powder, Er2Ti2O7, was measured to be a = 10.07522(9) {\AA}. Single crystals grown by the conventional floating zone (FZ) technique were Ti deficient (stuffed) and darker in color due to oxygen vacancies. Using the traveling solvent floating zone (TSFZ), a high structural quality, transparent and stoichiometric Er2Ti2O7 single crystal was grown at a lower temperature using the TiO2 solvent. Heat capacity measurements of the TSFZ grown Er2Ti2O7 crystal and stoichiometric powder exhibited a very close magnetic transition temperature TC ~1.23K that was suppressed in off-stoichiometric samples, demonstrating correlations between stoichiometry and ground state magnetism in Er2Ti2O7.