Ferroelectric potassium lithium niobate crystals grown by the vertical Bridgman method

Ferroelectric potassium lithium niobate (KLN) single crystals are very prom ising candidates for direct second harmonic generation of semiconductor dio de lasers. In this paper, crack-free KLN crystals up to 10 mm in diameter b y 50 mm in length were grown by the modified vertical Bridgman method from potassium and lithium enriched solutions. Prior to growth, KLN powder was p repared by sintering the mixture of K2CO3. Li2CO3 and Nb2O5 at 850 degreesC for 8 h. Two temperature zones were designed in the Bridgman furnace to pr event crystals cracking. The growth rate is less than 0.25 mm h(-1) and the temperature gradient in the solid-liquid interface is about 20 degreesC cm (-1). The transparent KLN crystal has a very good transmittance in the 420- 800 nm region with an absorption edge at 378 nm. Dielectric constant of eps ilon (33) and epsilon (11) at room temperature are 127 and 376, respectivel y. Curie temperature of the crystal is about 380 degreesC. (C) 2001 Elsevie r Science B.V. All rights reserved.