Potassium Lithium Niobate Crystals Research Articles

The role of alkali additives in the crystallization of ferroelectric potassium lithium niobate crystals

Ferroelectric K3Li2Nb5O15 (KLN-1) crystals have been grown by the top-seeded solution growth method from pure, Na+, Rb+ and Cs+ doped melt. The impact of alkali additives was assessed all over the entire pulling range by investigating the variation of the structural and physical properties by using spectroscopic and dielectric methods. The incorporation of alkali homologs has been correlated with their ionic radii: Na+ ions were found to enter both Li and K sites with high segregation coefficient (k∼1.6), Rb+ ions were detected only at K sites (k∼0.34) and Cs+ ions practically did not incorporate into the lattice (k∼0.12). Alkali additives have been found to play a dual role in the growth process by affecting the crystallization temperature and promoting the K and Li site occupancy. By decreasing the crystallization temperature the Cs2O additive reduced the concentration both of the antisite Nb ions at Li site and that of alkali vacancies; therefore it can be considered as a promising fluxing agent in the growth of KLN crystals.

Compositional Dependence and Structure of Hydroxyl Ion Defects in Ferroelectric Potassium Lithium Niobate

The OH– stretch mode spectra have been measured in both ferroelectric (KLN-1) and non-ferroelectric (KLN-2) potassium lithium niobate crystals grown from different melt compositions. O─H bond directions of about 15, 60, and 15 degrees with respect to the c-axis have been determined for the three main OH– bands in KLN-1 peaking at about 3440, 3500, and 3520 cm−1, respectively. Correlations have been found along the growth axis of the crystal between the decrease of the excess Nb content, the change of the hydroxyl band components at 3440 and 3520 cm−1, and the Raman modes at 540 cm−1 and 640 cm−1.

Growth of Na modified potassium lithium niobate crystal by the Czochralski method

Transparent Na modified potassium lithium niobate (Na0.23K2.60Li1.82Nb5.35O15.70; NKLN) crystal was successively grown by the Czochralski method using RF induction heating from melt composition Na2O:K2O : Li2O:Nb2O5=2:30:25:43mol%. NKLN crystal showed a tetragonal tungsten bronze structure with lattice constants a=12.5446±0.0010Å and c=4.0129±0.0005Å at room temperature. The dielectric constant along the c-axis ε33 showed a sharp maximum around 480°C. Optical transmission edge was 370nm and optical transmission spectra showed no absorption at wavelengths ranging from 380 to 800nm. The structural and optical properties of NKLN were similar to those of the near stoichiometric KLN crystals. We believe that the growth of NKLN by the Czochralski method has an advantage for a large size and high-quality crystal.

Fabrication and Characterization of Ion-Exchanged Optical Waveguides in Potassium Lithium Niobate Crystal Substrates

Optical waveguides have been successfully fabricated in KLN crystal substrates using the ion-exchange process for the first time. Only the TM mode can be guided in such waveguides. The refractive index profile of the waveguide can be approximately fitted by a complementary error function. To understand how the ion-exchanged waveguide is formed in the KLN substrate, an Rb+–K+ ion-exchange mechanism was proposed. After ion exchange, the structural alternation between substrate and ion-exchanged layer was investigated using the X-ray diffraction method. The waveguide transmission loss was measured.

Growth and characterisation of ferroelectric potassium lithium niobate crystals

Potassium lithium niobate crystals have been grown by the resistance heating Czochralski technique. The optical transmission spectrum of the crystal has been determined. The results showed that the spectrum properties of potassium lithium niobate crystals grown from a melt with a higher Li2O content are better than that of crystals grown from the melt with a lower Li2O content. The crystals grown by this method have good quality and second harmonic generation properties. Frequency doubling results of a quasi cw-Ti:sapphire laser using crystal samples showed that potassium lithium niobate can be used to double the frequency of near infrared quasi cw-lasers in the 890–960 nm wavelength range.

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 K 2CO 3, Li 2CO 3 and Nb 2O 5 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 ε 33 and ε 11 at room temperature are 127 and 376, respectively. Curie temperature of the crystal is about 380°C.

Cracking mechanism of the potassium lithium niobate crystal related to its internal structure

The potassium lithium niobate (KLN) crystal is attractive due to its excellent second harmonic generation (SHG) properties. It is difficult to get large sized samples because of cracking. In this paper, the cracking mechanism of the KLN crystal in relation to its structure is based on the cracking morphology, the thermal mechanical analysis, and crystallochemistry. It is found that the cracking always occurs parallel to the cleavage plane (001) and that the surface cracking lines are perpendicular to the [001] direction. The cracking is due to the thermal stress generated by the big difference in the thermal expansion coefficients along different directions during the cooling process after the crystal growth. From 600°C to 20°C, the KLN crystal exhibits a linear expansion along the [110] direction, but a large contraction along the [001] direction. The contraction along the [001] direction increases with decreasing content of Nb. The formation mechanism of the observed cracking is also discussed by the crystallochemistry approach in which the generation of cracking is related to the anisotropy of the inter-atom bond strength.

Influence of [K]/[Li] and [Li]/[Nb] ratios in melts on the TSSG growth and SHG characteristics of potassium lithium niobate crystals

KLN crystals were grown along the 〈110〉 axis by the TSSG method from different melts with 30–32mol% K2O, 23–27mol% Li2O and 43–46mol% Nb2O5. Lattice constants were measured by the single crystal XRD analysis. Curie temperatures were determined with an LCR meter HP 4284A at 1kHz. The blue SHG characteristics of the KLN crystals were investigated by using a 3900S Ti: sapphire CW tunable laser with the wavelength range of 675–1100nm. It is found that the non-critical phase matching (NCPM) wavelength at room temperature decreases significantly from 974 to 827.4nm with the increase of [K]/[Li] and [Li]/[Nb] ratios in the melts. On the basis of this survey, the melt compositions suitable for the TSSG growth of high quality KLN crystals with high lithium content are outlined, as indicated by the large c-axis lattice constant, high Curie temperature and short NCPM wavelength.

A ferroelectric frequency-doubling material-potassium lithium niobate

The ferroelectric potassium lithium niobate crystal has been the material expected hopeful to provide directly the doubling of the frequency of a semiconductor near-infrared CW-laser. Perfect crystals have been grown. The frequency-doubling properties have been studied using a CW Ti:sapphire laser at room temperature. The crystal showed good second harmonic generation properties.

Impedance Spectra near the Phase Transition Temperature of Potassium Lithium Niobate Crystals

The impedance spectroscopy of potassium lithium niobate (KLN) crystals was investigated over the frequency range of 100 Hz to 1 MHz in the temperature region of room temperature to 600°C. Above and below the phase transition temperature, the AC complex impedance is explained by the Cole-Cole semi-circle, with a temperature-dependent factor indicating the degree of distribution of the relaxation time. However, near the phase transition temperature, a skewed semi-circle was found. The frequency dispersion of the AC complex impedance near the phase transition temperature is different from that above and below the phase transition temperature. The two distinct slopes and the differences in the frequency variation of the imaginary part of impedance suggest that two dispersion mechanisms are involved. In the vicinity of the phase transition temperature at a low frequency, the AC complex impedance is influenced by a mobile charge carrier.

Magnesium-doped potassium lithium niobate crystal and its properties

High quality magnesium-doped potassium lithium niobate (designated as KLN:Mg) single crystal was grown for the first time. The tetragonal tungsten bronze structure of the Mg:KLN crystal was determined by X-ray powder diffraction, in which the lattice parameters were a=1.262nm and c=0.398nm. High temperature X-ray diffraction patterns showed that the expansion of the lattice with increasing temperature was less than that of the undoped crystal. The transmittance of the as-grown crystal was measured. It increased by 80% from the cutoff wavelength 380nm to 450nm. The transmittance for 404nm was 50%, which is larger than that of the undoped crystals. The frequency-doubling property of KLN crystal was analyzed. Preliminary frequency doubling experiments showed that the crystal could generate blue light of 404nm through noncritical phase matching (NCPM) second harmonic generation (SHG) using a 808nm diode laser at room temperature.

Growth of Potassium Lithium Niobate Crystals by Continue-Charged Czochralski Method

Growth of Potassium Lithium Niobate Crystals by Continue-Charged Czochralski Method

The growth and properties of magnesium-doped potassium lithium niobate crystal

Tetragonal tungsten bronze-type magnesium-doped potassium lithium niobate single crystal with a dimension of 10×10×40 mm 3 was grown for the first time by slow pulling method from high-temperature solution. The as-grown crystal has a perfect square shape without cracks. Annealing experiment showed that the crystal does not crack when heating and cooling through paraelectric/ferroelectric phase transition temperature. X-ray powder diffraction experiment showed that the unit cell parameters of KLN : Mg is slightly changed by the dopant. Blue–violet laser light at wavelength 404 nm has been achieved by noncritical phase matching second harmonic generation (NCPM SHG) of 808 nm laser diodes at room temperature.

Top seeded solution growth and characterisation of ferroelectric potassium lithium niobate crystals

We have grown KLN crystals from different melts by the TSSG method at our laboratory. The melting and crystallisation behaviours of the raw materials have been studied by the DTA method. The crystal compositions were measured by chemical analysis and the solute segregation effects between the melt and crystal were discussed. The crystal structure and optical properties were characterised by means of XRD and optical spectrum measurement. The blue SHG effect of the as-grown crystals was also examined by a dye laser.

Low Temperature Phase Transition of a Crystal in the Potassium Lithium Niobate System

A potassium lithium niobate crystal with tetragonal tungsten bronze structure was prepared by the Czochralski technique. The dielectric and pyroelectric properties were investigated in the temperature range of 300 to 10 K. A broadened ferroelectric-ferroelectric transition between phases with space group 4mm and space group m was found at about 80K.

Morphological aspects of potassium lithium niobate crystals with acicular habit grown by the micro-pulling-down method

Crack free a- and c-oriented potassium lithium niobate (K 3Li 2- x Nb 5+ x O 15+2 x , KLN) micro single crystals, with diameter up to 500 βm and length up to 10 cm, were grown by the micro-pulling-down (μ-PD) method in the melt composition range of -0.6≦ ×≦0.5. Whereas a-oriented crystals show mostly rectangular cross-sections with somewhat elongated dimension parallel to the c-axis, c-oriented crystals possess polygonal cross-areas, the symmetry of which is affected by the symmetry of the heat field very sensitivity. It has been shown that the Nb: Li relation in the starting melt is of considerable influence on the mode of growth kinetics. The second harmonic generation of Ti:sapphire and (Ga,A1)As lasers was provided successfully.

Resonantly enhanced, frequency doubling of an 820 nm GaAlAs diode laser in a potassium lithium niobate crystal

A potassium lithium niobate crystal was used to double the resonantly enhanced emission of an 820 nm GaAlAs, single-mode diode laser. With a passive resonator enhancement factor of 73 and 11.5 mW of incident near-infrared power, 0.36 mW of second harmonic were produced in quasi-cw operation. The optical quality of the crystal is described and compared with that of KNbO3.