Zone-leveling Czochralski growth and characterization of undoped and MgO-doped near-stoichiometric lithium tantalate crystals

Abstract

Undoped and MgO-doped near-stoichiometric lithium tantalate (SLT) crystals were grown by the zone-leveling Czochralski (ZLCz) technique for the first time from Li-rich solutions (mixed with 1.2 mol% MgO for MgO-doped SLT crystal) having Li-excess feed supplied from below in an iridium crucible. Inclusion-free crystals were obtained. The transmittance along the growth axis was found to be satisfactory (75±1%) having an absorption edge at 264.1±0.5 nm for undoped and 264.8±0.4 nm for MgO-doped SLT crystals. The refractive indices of the crystals were found to be n o=2.1768 and n e=2.1750±0.0002 for undoped and n o=2.1768 and n e=2.1784±0.0006 for MgO-doped SLT crystals, respectively. The Curie temperature and coercive field for the crystals were measured to be 680±3 °C and 1.95±0.65 kV/mm for undoped and 689±0.7 °C and 3.55±0.95 kV/mm for MgO-doped SLT crystals, respectively. ICP measurement gives the Li/Ta ratios as 0.995±0.002 and 0.9755±0.0145 in undoped and MgO-doped SLT crystals, respectively. The Mg/Ta ratio in MgO-doped crystal was measured to be 0.001235±0.00035. The Li/Ta ratio was found to vary along the crystal length in undoped and MgO-doped SLT crystals. The variation of the Mg/Ta ratio in MgO-doped SLT crystals is explained by mass balance equation.