Preparation and characterization of nanocrystalline potassium lithium niobate powders and films
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Potassium lithium niobate (KLN) powders and thin films were prepared from metalorganic compounds through the sol-gel process. A homogeneous and stable KLN precursor was synthesized by mixing the metal ethoxides. Powder gels were obtained through the hydrolysis of the solution by exposing it to the ambient atmosphere. Thin films were deposited on Si, SiO2/Si, and fused quartz by a spin coating technique. The pyrolysis and crystallization of KLN powders and films were investigated through the methods of differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and Raman scattering spectroscopy. The results revealed that both KLN powders and films could crystallize into a tetragonal tungsten–bronze-type phase with appropriate annealing. Optical studies indicated that the films were highly transparent in the visible–near-infrared wavelength range and could support optical modes.
I. INTRODUCTION
Potassium lithium niobate in the composition of K3Li2−xNb5+xO15+2x (KLN, 0.15 < x < 0.5) is a ferroelectric material with the tetragonal tungsten–bronze-type structure. KLN exhibits excellent electro-optic and nonlinear optical effects and has recently been identified as a promising material for blue laser operation through second harmonic generation (SHG) of commercially available GaAs/(Al,Ga)As diode lasers due to its large optical nonlinearity, short cutoff wavelength, high optical damage threshold, and wide noncritical phase matching properties at room temperature.1–7 It also exhibits a better mechanical stability over KNbO3, which substantially scales down the depoling caused by certain mechanical shocks and temperature fluctuations. Moreover, the phase-matching wavelength of KLN in SHG can be adjusted to the laser wavelength by varying the content of lithium in the composition. KLN crystals have earlier been grown by Kyropoulos,8 Czochralski,9,10 and topseed solution growth (TSSG)11–13 methods. These techniques often result in cracked crystals because of the compositional fluctuation due to the nonunit effective segregation coefficients of the solutes during growth and the large lattice variation and phase transition with temperature change during cooling. Recently, both the micropulling-down (-PD) technique14 and the laser-heated a)
Address all correspondence to this author. Present address: Lightwaves2020, Inc., 1323 Great Mall Drive, Milpitas, CA 95132. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 12, Dec 2001
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pedestal growth (LHPG) method15–17 were used to grow KLN fiber crystal, but it is still difficult to grow homogeneous crystals with sufficient size and uniform composition. KLN film obviously offers an alternative for the fabrication of compact and integrated blue lasers and waveguide modulators. A good recent example related to this scheme is the realization of blue-violet laser via SHG in a waveguide.18 In addition, KLN films can also find applications in surface acoustic wave (SAW), pyroelectric, and piezoelectric
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