Traveling solvent floating zone growth and anisotropic ionic conductivity of Li<i>_x</i>La₍₁₋<i>_x</i>_)/3TaO₃ single crystals

Abstract

In this study, single crystals of double-perovskite-type oxide Li x La (1¹x)/3 TaO 3 (LLTaO) were successfully grown using the traveling solvent floating zone (TSFZ) method. The Ta-rich phase, which was precipitated in the crystals, was grown via the conventional floating zone (FZ) growth process, indicating that LLTaO behaved as an incongruent melt. For the TSFZ growth for solvents with a LiTa 3 O 8 composition of 8 %, which is less than the LLTaO (x = 0.18) stoichiometric composition, the black grown crystals were homogeneous and crack-free, with a typical size of approximately 20 mm in length and 5 mm in diameter. The grown crystals turned colorless and transparent after being left overnight in the air at room temperature (about 25 °C). The Li concentration in the grown crystals was determined to be x = 0.086(1). This value is lower than the nominal composition (x = 0.18) of the feed owing to Li evaporation during the crystal growth. The ionic conductivities of the grown crystals along [110] and [001] were 2.8 © 10 ¹5 and 1.8 © 10 ¹5 S•cm ¹1 , respectively. The anisotropic parameter was determined to be 1.56 indicating that the ionic conductivity along the ab-plane is higher than that along the c-axis. Furthermore, the calculated activation energies along [110] and [001] were 0.29 and 0.34 eV, respectively.