• Title/Summary/Keyword: Crystal phase

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Change in the Order of the Phase Transition in Triglycine Selenate Crystal

  • Song, Yong-Won
    • The Korean Journal of Ceramics
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    • v.6 no.1
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    • pp.6-8
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    • 2000
  • The specific heat of a partly deuterated triglycine selenage (DTGSe) crystal under $\gamma$-irradiation was measured. It was shown that $\gamma$-irradiation defects changed the thermodynamic behavior of DTGSe crystal in a small dose region. The order of the phase transition changed from the first to the second at D=0.3 MR.

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Two dimensional Phase Transition of Liquid Crystal Film (액정박막에서의 2차원 상전이)

  • Jung, C.S.;Xue, J.Z.;Kim, M.W.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1993.05a
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    • pp.119-121
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    • 1993
  • Two dimensional phase transition and three dimensional propagation of layer structures of liquid crystal film are investigated by using surface second harmonic generation method. We have found a distinctive first order phase transition between a monolayer phase and a stable 3-layer phase of 8CB liquid crystal film.

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Dual Frequency Switchable Flexoelectric Cholesteric Devices

  • Chien, Liang-Chy;Shi, Lei
    • 한국정보디스플레이학회:학술대회논문집
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    • 2005.07a
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    • pp.105-108
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    • 2005
  • We demonstrate an electro-optical device based on the flexoelectric effect of a short-pitched cholesteric liquid crystal. By using a dual-frequency switchable nematic, a small amount of chiral dopant and a small amount of phase-separated polymer localized on the surface, we were able to create a device that operates in amplitude (flexoelectric) and phase(dielectric) modes. At high frequency the dual frequency liquid crystal suppresses the phase mode at higher voltage, which improves the switching speed, and thereby preserving the in-plane-switching mode.

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A Low Close-in Phase Noise 2.4 GHz RF Hybrid Oscillator using a Frequency Multiplier

  • Moon, Hyunwon
    • Journal of Korea Society of Industrial Information Systems
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    • v.20 no.1
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    • pp.49-55
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    • 2015
  • This paper proposes a 2.4 GHz RF oscillator with a very low close-in phase noise performance. This is composed of a low frequency crystal oscillator and three frequency multipliers such as two doubler (X2) and one tripler (X3). The proposed oscillator is implemented as a hybrid type circuit design using a discrete silicon bipolar transistor. The measurement results of the proposed oscillator structure show -115 dBc/Hz close-in phase noise at 10 kHz offset frequency, while only dissipating 5 mW from a 1-V supply. Its close-in phase noise level is very close to that of a low frequency crystal oscillator with little degradation of noise performance. The proposed structure which is consisted of a low frequency crystal oscillator and a frequency multiplier provides new method to implement a low power low close-in phase noise RF local oscillator.

Experimental and Numerical Study on Anisotropic Phase Separation of Liquid Crystal and Polymer Composites Cell Gap Variation

  • Jin, Min-Young;Bae, Ji-Hong;Kim, Jae-Hoon
    • 한국정보디스플레이학회:학술대회논문집
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    • 2007.08a
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    • pp.567-570
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    • 2007
  • Cell gap dependence on anisotropic phase separation was studied. The results showed that the morphology of phase separation depended on cell gap and material parameters. With numerical simulation and experiments, the optimal range of cell gap in the formation of polymer layer and liquid crystal was suggested for given material parameters.

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Synthesis and Mesomorphic Properties of New Achiral Liquid Crystals with 3-Alkoxy-2-(alkoxymethyl)-1-propoxy Swallow-Tails

  • Kang, Kyung-Tae;Kim, Jeong-Tak;Hwang, Ryeo-Yun;Park, Song-Ju;Lee, Seng-Kue;Lee, Jong-Gun;Kim, Yong-Bae
    • Bulletin of the Korean Chemical Society
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    • v.28 no.11
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    • pp.1939-1944
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    • 2007
  • New liquid crystalline (biphenylcarbonyloxy)benzoates with an achiral swallow-tail derived from 3-alkoxy-2- (alkoxymethyl)-1-propanol [(ROCH2)2CHCH2OH, R = Me, Et, Pr, Bu] were prepared. These liquid crystals exhibited the phase sequence (I-SmA-SmCalt-(SmCX)-Cr) and showed antiferroelectric-like Smectic C phase (SmCalt) at temperature lower, and temperature range broader than do the compounds containing a branched alkyl group as a swallow-tail. The temperature ranges of antiferroelectric phase were found to be 30-90 oC and crystallization temperatures were 4-60 oC. The binary mixture of an achiral swallow-tailed liquid crystal and a chiral antiferroelectric liquid crystal, (S)-MHPOBC showed antiferroelectric smectic C phase at temperature much lower than the single chiral antiferroelectric liquid crystal does.

Electrical Conductivity Properties of the $a-In_{2}Se_{3}$ Single Crystal ($a-In_{2}Se_{3}$ 단결정의 전기전도도 특성 연구)

  • 김형곤;김남오;이우선
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.14 no.8
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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.

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The Physical Properties of Thermotropic Side-Chain Triblock Copolymers of n-Butyl Acrylate and a Comonomer with Azobenzene Group

  • Dan, Kyung-Sik;Kim, Byoung-Chul;Han, Yang-Kyoo
    • Macromolecular Research
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    • v.17 no.5
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    • pp.313-318
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    • 2009
  • The side chain liquid crystal triblock copolymers (TBCs), which underwent phase transitions below their decomposition temperature, were prepared by copolymerization of poly(n-butyl acrylate) and a comonomer containing the mesogenic azobenzene group. The physical properties of TBCs in the distinctive transition temperature ranges were investigated in terms of the liquid crystal (LC) content in the copolymers. The phase transition temperatures traced optically, thermally and rheologically were well coincided one another and clearly exhibited the phase transition of smectic-nematic-isotropic with increasing temperature. In the smectic phase, increasing temperature made the liquid crystal system more elastic, but viscosity (${\eta}'$) remained almost constant. In the nematic phase, increasing temperature abruptly decreased ${\eta}'$ and G', ultimately leading to isotropic phase. Both smectic and nematic phases exhibited Bingham viscosity behavior but the former gave much greater yield stress at the same LC content.

Investigations of the Phase Behavior of N-dodecanocyl-N-methyl amido polyol carboxyl alkyl ether/N-dodecanocyl-N-alkyl Glucamine/Water System (N-도데카노실-N-메틸 아미도 폴리올 카르복시 알킬 에테르/(N-도데카노실-N-알킬 글루카민)/물계에서의 상거동 관찰)

  • Kang, Yun-Seog;Nam, Ki-Dae
    • Journal of the Korean Applied Science and Technology
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    • v.14 no.3
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    • pp.23-28
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    • 1997
  • The phase diagram for the surfactant mixture system of N-dodecanocyl-N-methyl amido polyolcarboxyl alkyl ether(DGC)/N-dodecanocyl-N-alkyl glucamine(DG)/water was studied usingpolarized microscopy, differential scanning calorimetry(DSC) and rheological measurements respectively. Using polarized microscopy, the textures of liquid crystal phases obtained at various surfactantconcentrations were investigated as a function of surfactant concentration and temperature, and phasetransitions between anisotropic liquid crystal phases and isotropic liquid phase were examined usingDSC measurements. Viscoelastic properties of surfactant solutions determined between hexagonal andlamellar liquid crystal phase by rheological measurements were approximately consistent with the resultsobtained by polarized microscopy and DSC. In the study for the phase of DGC/DG(5:5 mol ratio)/water system. It could be found that the hexagonal liquid crystal phase appeared at 25${\sim}$60wt% ofsurfactant, the cubic liquid crystal phase at 50${\sim}$65wt% and the lamellar crystal phase at above 70wt%.

The Effect of Layer Spacing Changes in the SmA Phase on Defects Observed in SSFLC Devices.

  • Wang, Chenhui;Bos, Philip J.;Kumar, Satyendra;Wand, Michael;Handschy, Mark
    • 한국정보디스플레이학회:학술대회논문집
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    • 2004.08a
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    • pp.193-197
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    • 2004
  • The effect of the temperature dependence of the smectic layer spacing in the smectic-A (SmA) phase on the formation of defects in the ferroelectric smectic-$C^{\ast}$ ($SmC^{\ast}$) phase is investigated with x-ray scattering technique. The study is based on thin parallel-aligned surface stabilized ferroelectric liquid crystal cells with two different alignment conditions, high pretilt $SiO_x$, alignment and low pretilt polyimide films. It is found that defects observed in the $SmC^{\ast}$ phase have much more profound dependence on the layer changes and chevron formation in the SmA phase than in the $SmC^{\ast}$ phase. We find that thermal layer expansion with decreasing temperature in the SmA phase suppresses the formation of defects observed in the SmC phase.

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