• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.197-201
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• 2010

$ZnWO_4$ nanocrystallines were prepared from polymeric complex method using microwave irradiation. The average nanocrystalline sizes were 18~25 nm showing an ordinary tendency to increase with the temperatures from 400 to $600^{\circ}C$. Bulk type single crystals of $ZnWO_4$ were grown successfully in the [100], [010] and [001] directions using the Czochralski method. The effect of the growth parameters, such as the rotation speed, pulling rate and diameter of the grown crystals, were examined. The hardness, thermal expansion coefficients and dielectric constants of the crystals were evaluated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.265-271
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• 2013

Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal for LED application. In this study, the inductively-heated CZ growth processes for the sapphire crystal of 300 mm length have been analyzed numerically using finite element method. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The results show that the solid-liquid interface height decreased from about 80 mm at initial stage to 40 mm after mid-stage due to achieve the growth speed balance. Also the optimal input power of the modified system was similar with the original one due to the compensation effects of the crucible geometry and additional insulation. The crystal temperature grown by the modified CZ grower was increased about 10 K than the original one. Therefore the sapphire crystal of 300 mm height was grown successfully.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.179-184
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• 2018

To lessen oxygen concentrations in a wafer through modifying the length of graphite heaters, we investigated the influence of relative distance from heater to quartz crucible on temperature profile of hot-zone in Czochralski silicon-crystal growth by simulation. In particular, ATC temperature and power profiles as a function of different ingot body positions were investigated for five different heater designs; (a) typical side heater (SH), (b) short side heater-up (SSH-up), (c) short side heater-low (SSH-low), (d) bottom heater without side heater (Only-BH), and (e) side heater with bottom heater (SH + BH). It was confirmed that lower short side heater exhibited the highest ATC temperature, which was attributed to the longest distance from triple point to heater center. In addition, for the viewpoint of energy efficiency, it was observed that the typical side heater showed the lowest power because it heated more area of quartz crucible than that of others. This result provides the possibility to predict the feed-forward delta temperature profile as a function of various heater designs.

• Journal of Sensor Science and Technology
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• v.6 no.1
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• pp.16-23
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• 1997

Bismuth germanate crystals well known as scintillator were grown by Czochralski method. In order to understand a mechanism of radiation resistance in Eu-doped BGO, we measured radiation induced-absorption spectra, excitation spectra, emission spectra and luminescence lifetimes of BGO crystals. We found that the charge transfer state of $Eu^{3+}$ ion is to play a key role to enhance the radiation resistance in BGO crystal. The $^{5}D_{0}$ emission of $Eu^{3+}$ ions that is not suitable for the radiation detectors due to a long decay time was found to be increased with increasing europium concentration. In the BGO crystal doped with 0.1 mole%, the density of radiation induced color centers was reduced about twenty times and the light output of $^{5}D_{0}$ was negligible by comparing to that of BGO.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.359-365
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• 1997

$K_2CoCl_4$, single crystals were grown by the Czochralski method in Ar atmosphere. The thermal hysteresis of the dielectric constant at $T_c$ was investigated. $K_2CoCl_4$ crystal shows ionic hopping mechanism due to $K^+$ ion and the activation energy is nearly 0.62 eV. Thermal expansions along a-, b-, and c-axis of $K_2CoCl_4$, were measured on heating and the thermal expansion coefficients in each phase were calculated. From the result of the optical absorption measurement, we interpreted the absorption peak as transition energy between the splitted energy levels of the Co ion in the crystal field and it showed the possibility of the application to the optical band filter between 800 nm and 1200 nm.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.111-119
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• 1992

Alexandrite crystals were grown by the Czochralski method. Relationships between or ystal quality and crystal growth factors such as pulling rate, rotation rate, purity of BeO po wders and evaporation loss compensation of BeO and Cr3+/Al3+substitution ratio were investigated. As a result, 1) high purity (more than 99.99p,) of BeO, as a raw material, is requisite condition for single crystal growth, 2) evaporation loss comp ensation is also requisite for high quality crystal growth. This compensation depends on pulling rate and Cr3+/Al3+ ratio. And 3) optimum pulling and rotation rate for alexandrite growth were 0.5∼1.0mm/hr and 20∼25rpm, respectively. Ale xandrite crystals were grown to (001) direction. Various types of defects were detected by the polarizing microscope and we discussed how to remove these defects. And room tempo rature absorption and fluorescence spectra were measured.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.525-531
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• 1998

A series of $LiNbO_3$ single crystals were grown by the Czochralski method from a congruent melt, a congruent melt with 0.05 mol% $Fe_2O_3$, a congruent melt with 6 wt.% $K_2O$ and a congruent melt with 6 wt.% $K_2O$ and 0.05 mol% $Fe_2O_3$ respectively. The growth of $LiNbO_3$ crystal from a congruent melt 6 wt.% $K_2O$ leads to nearly stoichiometric specimens. This is established by studying the following properties; XRD patterns, temperature dependences of the phase transition temperature, energy of the fundamental absorption edge, the shape of the absorption band of the $OH^-$vibration and linewidths of the ESR of $Fe_{Li}^{3+}$.

• Journal of Korean Ophthalmic Optics Society
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• v.2 no.1
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• pp.9-16
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• 1997

Ferroelectric $Pb_5Ge_{3-x}Ti_xO_{11}$(x=0, 0.015, 0.021, 0.03) single crystals were obtained from the melt by the Czochralski method. Grown crystals were pale brownish yellow and fully transparent. The dielectric relaxation of the $Pb_5Ge_{3-x}Ti_xO_{11}$ single crystals has been studied in the frequency range from 100 Hz to 10 MHz between $20^{\circ}C$ and $600^{\circ}C$. From the results of the these measurements. the temperature of the permittivity maximum was shifted to low temperature with increasing Ti content and the permittivity maximum decreased with increasing Ti content. The frequency dependent dielectric response of $Pb_5Ge_{3-x}Ti_xO_{11}$ single crystals exhibits a Debye type relaxation, with a distribution of relaxation times. Dielectric behavior is characteristic of carrier-dominated response.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.1
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• pp.20-29
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• 1992

In $BaTiO_3-NaNbO_3$ system, complete series of solid solution occurs and $30BaTiO_3{cdot}70NaNbO_3$ composition is congruently melted. Single crystals of $30BaTiO_3{cdot}70NaNbO_3$, composition were grown by Czochralski method in this investigation. Single crystals with dimensions of 15 - 20mm diameter and 20 - 30mm length, were grown at the pulling rate of 2.0mm/h and the rotation rate of 5.0 -l0rpm. Core structures were found in the grown crystals and inclusions, cellular boundaries existed at the core region. The origin of core occuring was unstability of the crystal- melt interface due to the poor conductivity of latent heat through the crystal during the crystal growing process. Obtained crystals were optically homogeneous except the core region and showed high optical transmittance in the visible range.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.278-285
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• 1998

It was known that the C-IC transition in the mixed crystal $(A_{1-x}A^'_x)_2ZnCl_4$ is smeared out with increasing x, which is attributed to the pinning effect of the doped A' ions. In this study, we introduce a new mixed crystal system $K_2Zn_{1-X}Co_XCl_4$, where doped Co ions do not destroy the orientation of the polarization in C phase and preserve the long range ordering of IC phase. We grew a series of mixed crystals $K_2Zn_{1-X}Co_XCl_4$ for x=0, 0.001, 0.005, 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 1 by the Czochralski method and investigated the real composition of the mixed crystals, structure and the change of the C-IC phase transition with increasing x by the thermal analysis.