The pyrochlore Ho2Ti2O7: Synthesis, crystal growth and stoichiometry

TL;DR

This study explores how synthesis and growth conditions affect the structural and magnetic properties of holmium titanate, demonstrating a method for producing high-quality, stoichiometric single crystals with improved low-temperature spin ice behavior.

Contribution

It introduces a controlled synthesis and crystal growth process for high-quality Ho2Ti2O7 crystals, emphasizing the importance of stoichiometry and growth conditions on magnetic properties.

Findings

Higher synthesis temperature yields single-phase compounds.

Stoichiometry affects lattice constant and magnetic freezing temperature.

Traveling solvent floating zone method produces high-quality crystals.

Abstract

We have investigated the effect of synthesis and growth conditions on the magnetic, structural, and compositional properties of pyrochlore oxide holmium titanate and demonstrate a method for growing high quality stoichiometric single crystals. A series of polycrystalline samples with various contents of Ti (-0.08 \leqslant x \leqslant 0.08, and nominal compositions of Ho2Ti2+xO7) were synthesized at different temperatures, and characterized using powder X-ray diffraction. The results show that synthesizing powders at a higher temperature of 1500 {\deg}C yield single phase compounds. Ti deficient powders showed an increase of lattice constant due to stuffing (Ho into Ti positions), while Ti rich powders showed a decrease in lattice constant due to anti-stuffing (Ti into Ho positions). A post annealing in O2 was found to be necessary to accomplish the anti-stuffing process. Use of the conventional floating zone (FZ) technique introduced Ti deficiency, stuffing, and oxygen vacancies in the grown crystal. Growth of high structural quality and stoichiometric single crystals of Ho2Ti2O7 by the traveling solvent floating zone (TSFZ) is reported. AC susceptibility measurements revealed that the stoichiometric crystal shows a higher ice freezing temperature, indicating that crystal quality and stoichiometry play a key role on low temperature spin ice properties of this compound.