Synthesis, crystal growth and characterization of the pyrochlore Er2Ti2O7

Abstract

Pyrochlore erbium titanate samples in the form of powders (with nominal compositions of Er₂Ti_2+xO₇, −0.08 ≤ x ≤ 0.08) and bulk single crystals were prepared to elucidate the effect of synthesis and growth conditions on their composition, structure, and transition temperature. All the samples were characterized using X-ray diffraction and specific heat measurements. Larger lattice parameters were measured for Ti-deficient stuffed powders, Er₂(Ti_2−xEr_x)O_7−δ, while Ti-rich anti-stuffed powders, (Er_2−xTi_x)Ti₂O_7+δ, showed a decrease in the lattice parameter. The lattice parameter for the stoichiometrically synthesized powder, Er₂Ti₂O₇, was measured to be a = 10.07522(9) Å. 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) method, a high structural quality, transparent and stoichiometric Er₂Ti₂O₇ single crystal was grown at a lower temperature using the TiO₂ solvent. The heat capacity measurements of the TSFZ grown Er₂Ti₂O₇ crystal and stoichiometric powder exhibited a very close magnetic transition temperature T_c of ∼1.23 K that was suppressed in off-stoichiometric samples, demonstrating correlations between the stoichiometry and ground state magnetism in Er₂Ti₂O₇.