• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.1
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• pp.43-50
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• 1992

$ LiNbO_3$ single crystals were grown using the Czochralski Method at various pulling speeds. Macroscopic defects such as cracks, bubbles and cellular structures were observed in some crystals. Cracks and bubbles observed in the crystals depended on the pulling speed and cooling rate. $ LiNbO_3$ crystals of about 15mm diameter could be grown properly at 6-7mm/h pulling speed and $ 20^{circ}C/h$ cooling rate. In order to investigate dielectric properties and optical properties for device application, these properties were measured for the sample cut along a axis and c axis at different temperatures.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.113-116
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• 1998

A numerical study was performed on the fluid flow in the melt of the cold model for Czochralski growth system. The fluid flow in the melt of Woods metal with crucible diameter of 20cm was calculated using a three dimensional finite difference method. Since the crucible size is large, fully turbulent model as well as laminar model was used in the calculation. The effects of crucible rotation rate, crystal rotation rate and wall temperature difference on the velocity and temperature distribution were also investigated. For the purpose of verifying the results of calculation, a cold model experiment using Woods metal was also conducted and the velocity distribution in the melt of the model was measured.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1015-1020
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• 1997

In the Nd;YAG crystal growth by Czochralski method, the relationship between the core formation and the solid-liquid interface was observed by controlling the temperature gradient in the furnace. When the crystal was grown along<111> direction, defects and core area were reduced as the temperature gradient increased. The optimum temperature gradient was found to be higher than 4$0^{\circ}C$/cm. The Nd3+ concentration analysis by ICP-Mass showed that the segregation coefficient was about 20% higher in the core region than core-free region, where the segregation coefficients of core region and core-free region were 0.22 and 0.18, respectively.

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.734-739
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• 2009

It is well known that the temperature and the flow pattern of the crystal-melt interface affect the qualities of the single crystal in the Czochralski process. Thus the temperature profile in the growth system is very important information. This work focuses on controlling the temperature of the silicon melt with a thermal gradient of the crucible. Therefore, the side heater is divided into three parts and an extra heater is added at the bottom for thermal gradient. The temperature of the silicon melt can be strongly influenced and controlled by the electric power of each heater.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.68-73
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• 2015

Single crystals of $Yb^{3+}$ doped $Y_3Al_5O_{12}$ up to 25 at.% were grown by the Czochralski method. Using the pulling rate of 0.8 mm/h and the rotation rate of 10 rpm, single crystals with diameters of up to 40 mm and lengths up to 160 mm were obtained. The growth atmosphere was either pure nitrogen or the mixture of nitrogen and oxygen. The crystal was bluish green when using pure nitrogen and the crystal was colorless when using the mixture of 99 % nitrogen and 1 % oxygen. The concentration of $Yb^{3+}$ ions decreased with increasing the length of the crystal and $Yb^{3+}$ concentration of core area was slightly higher than the other areas in the compositional analysis. The fluorescence lifetime decreased with increasing the doping concentration of $Yb^{3+}$ ions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.18-28
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• 1998

A laboratory experiment was made of a control of temperature oscillation in Czochralski convection. Numerical computation was also made to delineate the control of temperature oscillation. The suppression of temperature oscillation was achieved by varying the rotation rate of crystal rod ($\Omega=\Omega_0(1+A sin 2{\pi}ft/t_p)$), where A denotes the amplitude of rotation rate and f the frequency factor. Based on the inherent dimesionless time period of temperature oscillation ($t_p$), the suppression rate of temperature oscillation was characterized by the mixed convection parameter ($0.217{\leq}Ra/PrRe^2{\leq}1.658$). The optimal values of A and f were also scrutinized. To understand the suppression mechanism of temperature oscillation, the controls of isotherm($\theta$) and equi-vorticity($\omega$) were investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.4
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• pp.148-153
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• 2001

New piezoelectric $Ca_{3}NbGa_{3}Si_{2}O_{14}$ (CNGS) single crystal was grown using the Czochralski technique. The crystal structure of CNGS was found to be isostructural with $A_{3}BC_{3}D_{2}O_{14}$. The unit cell parameters were a=8.087 and c=4.983 and the space group was P321. The distribution of each cation was found to be ordered in each site. Some piezoelectric properties of CNGS are showed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.1
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• pp.1-10
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• 1996

A numerical study was conducted on the effects of the cusp magnetic field in 8" silicon single crystal grwoth by Czochralski method. For a damping effects simulation by magnetic field, low reynolds number ${\kappa} - {\varepsilon}$ model was adopted. Symmetrci cusp magnetic field has a effect of damping streamline crystal, is lowerd with the increasing cusp magnetic field intensity. The uniformity of the oxygen concentration was improved. The asymmetirc cusp magnetic field increased the oxygen concentration however, oxygen concentration distribution in the radial direction was remained uniform. Suitable combination of symmetric and asymmetric cusp magnetic fields could give uniform and low oxygen concentration in the axial direction.tion.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.526-526
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• 1996

The single crystal of LiTaO3 is well known eletro-optic material as well as the piezoelectric one applied to SAW filter. LiTaO3 has large electro-optic effects, so applied to optical switch, acosto-optic deflector, and optical memory device using photorefractive effects. The crystal growth of SAW-grade LiTaO3 has been studied many aspects, but there is no detail research about optic-grade crystal growth. The conditions of optic-grade LiTaO3 single crystal are as below. The optical transmittance must be over 75%, and axial and radial concentratiom uniformity below 1%. The variation of Curie temperature depending on Li/Ta ratio must be also below 2$^{\circ}C$ and no internal no internal cracks and defects. Because of the limitation of crystal quality, the growing of optic-grade LiTaO3 single crystal is very difficult compared with the growing of SAW-grade. In this research, upper conditions of optic-grade single crystal was investigated after growing of 1 inch diameter and 1.5 inch length LiTaO3 single crystal having no internal cracks and defects using Czochralski method. Curie temperature was determined with DSC and measuring capacitance and lattice parameter was calculated about the grown crystal and ceramic powder samples of various Li/Ta ratio. The result of Tc variation was below 1.2$^{\circ}C$ all over the grown crystal, so it is confirmed that LiTaO3 was grown under congruent melting composition having optical homogeniety. Also, the optical transmittance was about 78%, which was sufficient for optical device.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.6
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• pp.394-399
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• 2000

Langasite (LGS) is a material hoped to meet needs required of new base materials for future communication devices (e.g.SAW filters). In this study, synthesis of new materials was pursued by developing new compounds with the host structure of Langasite in hopes to obtain materials with improved characteristics; compounds including $La_3$$Ta_{0.5}$$Ga_{5.5}$$O_{14}$(LTG)and $La_3$$Nb_{0.25}$$Ta_{0.25}$$Ga_{5.5}$$O_{14}$(LNTG) were synthesized by solid state reactions. Characteristics of the compound synthesized in question were determined. The single crystals of Langasite-type were grown using the Czochralski method. The growth conditions for LTG and LNTG were studied and were found to be similar to those of LGS. The growth characteristics of LNTG were observed by studying etch pit formation density along the crystal length.