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

Abstract

K/sub 3/Li/sub 2/Nb/sub 5/O/sub 15/ (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 K/sub 2/CO/sub 3/, 17.3 mole % of Li/sub 2/O/sub 3/, and 47.7 mole % of Nb/sub 2/O/sub 5/. 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 /spl epsi//sub 11//sup T/ and /spl epsi//sub 33//sup T/ at room temperature were 318 and 106, respectively. The constant /spl epsi//sub 33//sup T/ showed a marked anomaly at the transition point of 430/spl deg/C. Pyroelectric constant p at room temperature was determined as 80 /spl mu/C/m/sup 2/K from the pyroelectric current method. Resistivity /spl rho/ 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.