• 한국세라믹학회지
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• 제46권4호
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• pp.419-424
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• 2009

Congruent or stoichiometric $LiNbO_3$ fiber single crystals were grown by the $\mu$-PD method, and the grown fiber crystals have the several (2 or 3) ridges with a diameter of $1.35{\sim}1.5\;mm$ and a length of $40{\sim}100\;mm$. In this $\mu$-PD process, different growth rates ($10{\sim}60\;mm/h$) were applied. Pt wire or $LiNbO_3$ crystal was used as a seed. The properties of grown $LiNbO_3$ fiber single crystals having a-axis or c-axis according to seeds were effected by the grown conditions(Pt tube diameter, pulling speed, after heater etc.). Disk-type $LiNbO_3$ samples were poled in condition of DC 5 V/cm at 1050, 1075 or $1100^{\circ}C$. XRD, SEM, conoscope image through the polarized microscope, $T_C$ measuring apparatus, optical transmittance measuring instrument are used to identify the properties of $LiNbO_3$.

• 한국전기전자재료학회논문지
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• 제26권12호
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• pp.863-866
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• 2013

SiC crystal ingots were grown on 6H-SiC dual-seed crystals with different surface roughness and different seed orientation by a PVT (Physical Vapor Transport) method. 4H and 15R-SiC were grown on seed crystal with high root-mean-square (rms) value. The polytype of grown crystal on the seed crystal with lower rms value was confirmed to be 6H-SiC. On the other hand, all SiC crystals grown on seed crystals with different seed orientation were proven to be 6H-SiC. The surface roughness of seed crystals had no effect on the crystal structure of the grown crystals. However, the crystal quality of 6H-SiC single crystals grown on the on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on the off-axis seed.

• 한국결정성장학회지
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• 제5권3호
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• pp.223-232
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• 1995

Urea($(NH_2)_2CO$) 및 THAMP(Tris(hydroxymethyl)aminomethane phosphate) 유기 단결정은 레이저의 파장변환소자등의 응용에 유용한 새로운 유기 비선형 광학재료(NLO)이다. 온도하강법과 온도차법을 이용하여 urea와 THAMP 유기 단결정의 육성을 시도하였으며 이들 방법에 따른 육성조건을 확립하였다. Urea의 용매로는 용해도의 측정을 통하여 메탄올이 가장 적합하였으며, 용해도에 대한 온도계수는 posotive였으며, 용해열은 - 2.58 kcal/mol이었다. 육성된 urea 결정은 z축의 성장이 지배적이었고, z축의 성장제어와 x, y축의 성장을 위하여 $NH_4_H_2PO_4$, KCL, $H_3PO_4$, $CaCl_2{\cdot}2H_2O$, $C_2H_5OH$의 첨가제를 사용하여 z축의 성장제어와 x, y축의 성장을 증진시켰다. THAM과 $H_3PO_4$의 화학 양론적 혼합비 1 : 1의 몰비로부터 양질의 THAMP 유기 단결정을 육성하였고 용해도에 대한 온도계수는 positive였으며, 용해열은 - 1.70 kcal/mol이었다.

• 한국결정성장학회지
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• 제9권5호
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• pp.463-469
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• 1999

$K_3$$Li_2$$Nb_5$$O_{15}$KLN) 단결정을 $K_x$$Li_{1-x}$$NbO_3$의 조성에서 x= 0.04~0.6으로 결정성장방법으로 성장시켰다. 균열이 없는 양질의 결정성장을 위해 c축 및 a축 방향을 택하였고, 단결정 성장을 위한 최적의 조건에 대하여 연구하였다. 성장된 결정은 편광현미경 관찰을 통해 일축성 무늬를 볼수 있었고, X-선 회절실험에서 결정된 격자상수는 a=b=12.500 $\AA$, c=3.996$\AA$이었으며, 1HF : $2HNO_3$ 용액의 부식에서 c축 방향으로 정사각형 및 a축 방향으로 직사각형의 부식상을 볼수 있었다. 광투과율 측정과 온도에 따른 유전상수 측정등을 통해 KLN 결정의 광학적 특성 및 다른 조성을 갖는 시료에서 유전특성을 조사하였다. $420^{\circ}C$에서 상전이 온도를 갖는 결정은 확산상전이(diffuse phase transition) 특성을 갖는 반면 $493^{\circ}C$에서 상전이 온도를 보이는 결정은 날카로운(shap) 유전특성을 나타내었다.

• Progress in Superconductivity
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• 제12권1호
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• pp.36-40
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• 2010

We have studied the anisotropy of the London penetration depth of carbon doped $MgB_2$ single crystals, which was obtained from reversible magnetization measurements with the magnetic field both parallel and perpendicular to the c-axis. Similar to the pure $MgB_2$, the anisotropy of the upper critical field ${\gamma}_H$ decrease with temperature while the anisotropy of the London penetration depth ${\gamma}_{\lambda}$ slowly increases with temperature. However, the temperature dependence of ${\gamma}_H$ is drastically reduced and the value of ${\gamma}_{\lambda}$ becomes nearly ~1 as C is introduced. These results indicate that C substitution increases impurity scattering mainly in the $\sigma$ bands. The temperature dependence of the anisotropies agree well with the theoretical predictions with impurity scattering.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.260-260
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• 1999

We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

• Progress in Superconductivity
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• 제8권2호
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• pp.132-137
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• 2007

We have studied superconducting parameters of $MgB_2$ single crystals from reversible magnetization measurements with the magnetic field both parallel and perpendicular to the c-axis of the crystals. The temperature dependence of the London penetration depth, ${\lambda}_{ab}{^{-2}}(T)$, obtained from the Hao-Clem analysis on reversible magnetization, shows a clear discrepancy from single-band theories. It is also found that the anisotropies of the London penetration depth, ${\gamma}_{\lambda}$, slowly increases with temperature while the anisotropy of the upper critical field, ${\gamma}_H$, decreases with temperature. These behaviors are in sharp contrast with the behavior of superconductors with a single band. The temperature dependence of ${\lambda}_{ab}{^{-2}}$, and the opposite temperature dependences of ${\gamma}_{\lambda}\;and\;{\gamma}_H$ can be well explained with the theory of the two-band superconductivity.

• 한국전기전자재료학회논문지
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• 제14권8호
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• pp.629-633
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• 2001

Electrical properties of the $\alpha$-In$_2$Se$_3$ single crystals grown by use of the Bridgman technique were examined in the transition temperature range between $\alpha$-phase and $\beta$-phase. $\alpha$-In$_2$Se$_3$ single crystal has ' the rhombohedral structure and lattice constants are a=4.025 $\AA$, c=28.771 $\AA$ in c-axis. The transition temperatures of the stoichiometric $\alpha$-In$_2$Se$_3$ single crystal is 198.8$^{\circ}C$ according to the specimens. The temperature of $\alpha$longrightarrow$\beta$ phase transition decreased but the temperature of $\beta$longrightarrow$\alpha$ phase transition increased as the number of heating-cooling cycle increased.

• 한국결정학회지
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• 제3권1호
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• pp.37-43
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• 1992

비선형광학 단결정인 KTiOP04는 Nd:YAG 레 이저의 제2고조파 발생장치로 가장 널리 이용되 는 물질이다. 본 연구에서는 낮은 점도를 갖는 3K2W04. P2O5 응제를 이용하여 TSSG법에 의한 KTiOP04 단결 정 육성 실 험 을 하였다. KTiOP04 육 성에 적합하도록 온도구배가 작은 전기로와 정밀 한 회전인상장치를 제작하였으며,용액 내 수직온도 구배는 용액표면과 용액 밑부분의 온도차가 1℃로 매우 작았다. 성장 과정의 관찰과 조절이 용이하도록 종자정을 용액 표면에 위치시켰다. 용액의 조성은 66.7mol%의 KTiOP04를 포함하도록 고정하였으며 이 용액의 포화온도는 1020℃ 였다. 냉각속도가 0 2℃/h, 결정의 회전속도가 50 rpm인 성장조건에서 a-, b-, c-축으로의 길이 가 각각 23 ×25 ×25mm3인 포유물이 없는 양질의 단결정을 얻을 수 있었다. 성장된 K,Tiop04 단결정은 크게 발달한 (201)면과 (011), (110), (100) 면들로 이루어져 있었으며 (101) 면이 관찰되기도 하였다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.321-335
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• 1999

Erbium(Er) doped LiNbO3(Er:LiNbO3) single crystal gibers were grown free of cracks along the c-axis by micro-pulling down method. the Er3+ concentration was distributed homogeneously along the growth axis. The samples for optical characterization were cut from as-grown single crystal fibers and polished. When the 980 nm light was incident on the sample, upconversion phenomena were observed at the green range of wavelength 510~570 nm. In addition, the intensity of upconversion was remarkably increased by increasing the concentration of Er2O3 dopant in as-grown Er:LiNbO3 crystals.