Ferroelectric potassium lithium niobate crystals grown by the vertical Bridgman method

Ferroelectric potassium lithium niobate (KLN) single crystals are very promising candidates for direct second harmonic generation of semiconductor diode lasers. In this paper, crack-free KLN crystals up to 10 mm in diameter by 50 mm in length were grown by the modified vertical Bridgman method from potassium and lithium enriched solutions. Prior to growth, KLN powder was prepared by sintering the mixture of K2CO3, Li2CO3 and Nb2O5 at 850°C for 8 h. Two temperature zones were designed in the Bridgman furnace to prevent 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°C 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 ε33 and ε11 at room temperature are 127 and 376, respectively. Curie temperature of the crystal is about 380°C.