Growth of potassium lithium niobate single crystals by the continuously-charged Czochralski technique

Abstract

Tungsten-bronze structure ferroelectric potassium lithium niobate (KLN) single crystals had been grown from incongruent melt. To avoid the deviation of the composition during the growth, an improved Czochralski method, continuously-charged Czochralski (CC-CZ) technique was used here. The KLN crystal with composition of K/sub 3/Li/sub 1.8/Nb/sub 5./ /sub 2/O/sub 15./ /sub 4/ was grown from 0.3K/sub 2/O-0.263Li/sub 2/O-0.437Nb/sub 2/O/sub 5/ melt. Calcined powders that had the same composition as the crystal were thrown into the melt during the growth to offset the compositional change. A 30 mm-long crystal was investigated for compositional deviation by measuring its Curie temperature using a differential scanning calorimetry (DSC). The results indicated that the crystal was compositionally deviation free. The crystal had absorption edge at 370 nm and showed optical absorption of less than 0.3 cm/sup -1/ at 420 nm. Both ordinary and extraordinary optical indices were measured by the least declinate method, and then fitted to the Sellmeier's dispersion relations. The wavelength of second harmonic generation at the noncritical matching angle was determined as 816 nm. A blue-violet SHG output beam with wavelength of 408 nm was observed. The nonlinear optic coefficient, d/sub eff/=1.2 d/sub eff//sup LN/ was obtained.