Synthesis, crystal growth and characterization of the pyrochlore Er2Ti2O7
Pyrochlore erbium titanate samples in the form of powders (with nominal compositions of Er2Ti2+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(Ti2−xErx)O7−δ, while Ti-rich anti-stuffed powders, (Er2−xTix)Ti2O7+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 Tc of ∼1.23 K that was suppressed in off-stoichiometric samples, demonstrating correlations between the stoichiometry and ground state magnetism in Er2Ti2O7.