Growth and properties of tungsten-bronze ferroelectric potassium lithium niobate single crystals for optical applications

K₃Li₂Nb₅O₁₅ (KLN) single crystals have been grown by the rf heating Czochralski technique from a melt with the potassium and lithium enriched composition, 35 mole % of K₂CO₃, 17.3 mole % of Li₂O₃ , and 47.7 mole % of Nb₂O₅. Optimum growth conditions were a pulling rate of 1 mm/h and rotation rate of 25-30 r.p.m. The pulling axis was chosen in parallel to the [110] axis in order to minimize the cracking during the growth. Transparent and pale-yellow crystals up to 10 mm in diameter and 20 mm in length were obtained. Dielectric constants ε₁₁^T and ε₃₃^T at room temperature were 318 and 106, respectively. The constant ε₃₃^T showed a marked anomaly at the transition point of 430°C. Pyroelectric constant p at room temperature was determined as 80 μC/m²K from the pyroelectric current method. Resistivity ρ showed a small change at the phase transition temperature. Further, it was found that the addition of small amount of Na to KLN results in more preferable electrooptic and nonlinear-optic behaviors than those of pure KLN