Impact of stoichiometry ofYb2Ti2O7on its physical properties

A series of ${\mathrm{Yb}}_{2+x}{\mathrm{Ti}}_{2\ensuremath{-}x}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ doped samples demonstrates the effects of off-stoichiometry on ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$'s structure, properties, and magnetic ground state via x-ray diffraction, specific heat, and magnetization measurements. A stoichiometric single crystal of ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ grown by the traveling solvent floating zone technique (solvent = 30 wt % rutile ${\mathrm{TiO}}_{2}$ and 70 wt % ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$) is characterized and evaluated in light of this series. Our data shows that upon positive $x$ doping, the cubic lattice parameter $a$ increases and the Curie-Weiss temperature ${\ensuremath{\theta}}_{\mathrm{CW}}$ decreases. Heat capacity measurements of stoichiometric ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ samples exhibit a sharp, first-order peak at $T=268$(4) mK that is suppressed in magnitude and temperature in samples doped off ideal stoichiometry. The full entropy recovered per Yb ion is 5.7 J ${\mathrm{K}}^{\ensuremath{-}1}\ensuremath{\approx}Rln2$. Our work establishes the effects of doping on ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$'s physical properties, which provides further evidence indicating that previous crystals grown by the traditional floating zone method are doped off ideal stoichiometry. Additionally, we present how to grow high-quality colorless single crystals of ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ by the traveling solvent floating zone growth method.