• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.341-345
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• 2012

[Li0.055(K0.5Na0.5)0.945](Nb1-xTax)O3 (0.05 ≤ x ≤ 0.25) ceramics were prepared by the partial sol-gel (PSG) method to improve the microstructure homogeneity of Ta5+ ion and were compared to those prepared by the conventional mixed oxide (CMO) method. For the PSG method, Ta(OC2H5)5 was directly reacted with calcined [Li0.055(K0.5Na0.5)0.945]NbO3 powders and the specimens sintered at 1100 ℃ for 5 hrs showed a single phase with a perovskite structure. Compared to the specimens prepared by conventional mixed oxide powders, the relative ratio of tetragonal phase to orthorhombic phase of the sintered specimens prepared by Ta(OC2H5)5 was larger than that of the sintered specimens prepared by Ta2O5. The electromechanical coupling factor (kp), piezoelectric constant (d33) and dielectric constant (εr) of the sintered specimens were increased with Ta5+ content. These results could be attributed to the decrease of the orthorhombic-tetragonal polymorphic phase transition temperature (To-t), which could be evaluated by oxygen octahedral distortion. Strain of the sintered specimens prepared by the PSG method was higher than that of specimens prepared by the CMO method due to the increase of relative density. The effects of crystal structure on the strain characteristics of the specimens were also discussed.

• 한국세라믹학회지
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• 제40권2호
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• pp.206-211
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• 2003

Sol-gel 공정으로 제조된 YMnO$_3$박막의 결정상과 강유전특성에 미치는 기판종류와 버퍼층의 영향에 대하여 고찰하였다. Si(1OO) 기판위에는 hexagonal YMnO$_3$이 형성되었으나 Pt(111)/TiO$_2$/SiO$_2$/Si 기판위에는 hexagonal과 orthorhombic YMnO$_3$이 함께 형성되었다. 기판위에 미리 $Y_2$O$_3$버퍼층을 형성시킨 경우에는 Si(100)와 Pt(111)/TiO$_2$/SiO$_2$/Si 두가지 기판 모두 단일 hexagonal YMnO$_3$이 성장하였으며, 특히 c-축 배향성이 향상되었다. 박막내에 hexagonal과 orthorhombic YMnO$_3$이 혼재된 시편보다는 hexagonal 단일상이 형성된 시편이, 또한 단일상 시편중에서도 c-축 우선배향성이 좋은 시편이 그렇지 않은 시편에 비해 누설전류밀도 특성이 우수하였다. YMnO$_3$박막의 잔류분극값은 Si(100)기판을 사용했을 경우, 버퍼층 없이 제조된 시편은 0.14, 버퍼층이 삽입된 시편은 0.24$\mu$C/$ extrm{cm}^2$의 값을 나타내었다 한편 Pt(111)/TiO$_2$/SiO$_2$/Si 기판의 경우, 버퍼층 없이 형성된 YMnO$_3$시편은 이력곡선을 보여주지 못하였고, 버퍼층이 삽입된 시편은 1.14$\mu$C/$\textrm{cm}^2$의 잔류분극값을 나타내었다. 이상의 연구를 통하여 기판의 종류와 $Y_2$O$_3$버퍼층 삽입으로 YMnO$_3$박막의 결정상과 배향성을 제어함으로서 박막시편의 누설전류밀도 특성 및 강유전특성을 제어할 수 있음을 확인하였다.

• 한국결정학회지
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• 제16권2호
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• pp.138-140
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• 2005

A new crystal of helminth glutathione S-transferase, 28 kDa isozyme from Clonorchis sinensis has been grown from a 20% PEG MME 550 solution containing 50 mM $CaCl_{2}$ in 0.1 M bis-Tris buffer (pH 6.5) in $2{\sim}3$ days. The crystals diffract to $3.0{\AA}$ resolution and belong to the orthorhombic space group $P2_{1}2_{1}2_{1}$ with cell parameters $a=62.58{\AA},\;b=69.92{\AA},\;and\;c=339.67{\AA}$.

• Advances in materials Research
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• 제2권1호
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• pp.1-13
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• 2013

Lead-free compound $(Na_{0.5}Bi_{0.5})(Zr_{0.75}Ti_{0.25})O_3$ was prepared using conventional ceramic technique at $1070^{\circ}C$/4h in air atmosphere. X-ray diffraction analysis showed the formation of single-phase orthorhombic structure. Permittivity data showed low temperature coefficient of capacitance ($T_{CC}{\approx}5%$) up to $100^{\circ}C$. Complex impedance studies indicated the presence of grain boundary effect, non-Debye type dielectric relaxation and evidences of a negative temperature coefficient of resistance. The ac conductivity data were used to evaluate the density of states at Fermi level and apparent activation energy of the compound.

• Bulletin of the Korean Chemical Society
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• 제29권8호
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• pp.1485-1490
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• 2008

Dumbbell-shaped aromatic amphiphilic molecules consisting of a dodeca-p-phenylene as a rigid segment and oligoether dendrons as a flexible chains were synthesized, characterized, and their aggregation behavior was investigated in the bulk and at the air-water interface. In contrast to the molecule 2 which shows a nematic liquid crystalline state, molecule 1 based on shorter dendritic chains was observed to self-assemble into a 3-D primitive orthorhombic supercrystal. And molecule 1 at the air-water interface was observed to reorganize from circular plates to ring structures by lateral compressions.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.17-19
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• 2002

Melt textured YBCO superconductors were fabricated by the top seeding method using Sml.8($Sm_{1.8}$ $Ba_{2.4}$ $Cu_{3.4}$$O_{7-Y}$) seed. We investigated the twin structures using the optical microscope, SEM and TEM. The twin structures formed during the tetragonal to orthorhombic transition which occurred at $450^{\circ}C$ in sample oxygen annealing. The twin structures were clearly observed by SEM due to the chemical etching effects. The lengths of twin structures were increased as the oxygenation heat treatment time increased from 1hr to 10hr. We investigated twin structure by TEM. The twin spaces were considered to be related to the oxygen contents. The results suggested an oxygen diffusion model for the formation of the twin lengths.

• 반도체디스플레이기술학회지
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• 제6권4호
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• pp.65-68
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• 2007

An epitaxial NiSi structure on Si (001) substrate was studied by using density functional theory (DFT). Orhorhombic and B2-NiSi structures were compared first. B2 structure was further considered as it has same crystal structure as Si and the lattice mismatch between B2 and Si is small, compared to orthorhombic-NiSi. The lattice parameters of x- and y-direction in B2-NiSi structure were modified to match with those in Si (001). The size reduction of the lattice parameter of B2-NiSi to match with that of Si increased the lattice parameter of z-direction by 10.5%. Therefore, we propose that an optimum structure of NiSi for epitaxial growth on Si (001) is a tetragonal structure.

• 한국결정성장학회지
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• 제7권1호
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• pp.117-125
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• 1997

강탄성 $CsPbCl_3$ 결정을 Czochralski법 및 Bridgman법을 사용하여 육성하고 XRD, DTA, 유전상수 측정 등을 통하여 구조 조사 및 상전이 온도를 확인하고 편광현미경 조사를 통하여 강탄성 domain의 존재를 확인하였으며 domain의 온도 의존성 등을 관찰하였다. 또한 cubic상에서 tetragonal, orthorhombic을 거쳐 monoclinic으로 상전이하였을 때 나타나는 domain들의 orientation에 대해 결정학적 고찰을 통하여 그리고 이론적으로 조사하여 일치되는 결과를 얻었다.

• 한국초전도ㆍ저온공학회논문지
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• 제6권1호
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• pp.1-5
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• 2004

Long length of Bi-2223/Ag superconducting wives were fabricated by stacking and drawing process with advanced heat-treatment schedules. Intermediate annealing was carried out to increase the homogeneity and uniformity of the superconducting filaments embedded in the silver matrix. Phase modification from tetragonal to orthorhombic Bi-2212 by pre heat treatment(PHT) was executed to improve the texture and phase transformation of Bi-2223. Drawing stress was measured to predict the sausaging and stress limit. Rolling Parameters such as thickness. width and winding tension were investigated to roll the tape with uniformity. 1 km length of Bi-2223/Ag superconducting wires were fabricated without any breakage. Critical current (Je) of 270 m length of superconducting tapes was measured over than $70 A/cm^2$ continuously after final sintering.

• 자원환경지질
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• 제32권4호
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• pp.399-409
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• 1999

Mullitization of kaolinite and dickite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in dickite is identical with that in kaolinite except that cristobalite is crystallized at $50^{\circ}C$ higher temperature in dickite. Difference in phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metadickite and metakaolinite on the effect of impurities. A part of quartz is transformaed into cristobalite. Spinel-type phase produced in disordered kaolins including illite occurs over a short range of temperatures. Primary mullite is transformed into orthorhombic mullite at higher temperature as well. These results sustain the idea that disintegration of methkaolin and the spinel-type phase supplies extra sillica and promotes the growth of mullite cristobalite.