• Title/Summary/Keyword: phase transition

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Molecular Dynamics Study on the Structural Phase Transition of Crystalline Silver Iodide

  • Jun Sik Lee;Mee Kyung Song;Mu Shik Jhon
    • Bulletin of the Korean Chemical Society
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    • v.12 no.5
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    • pp.490-494
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    • 1991
  • The ${\beta} to {\alpha}$ phase transition in silver iodide is studied with the (N, V, E) and (N, P, T) molecular dynamics (MD) method. In experiments, the phase transition temperature is 420 K. Upon heating of ${\beta}$ form, the iodine ions undergo hcp to bcc transformation and silver ions become mobile. MD simulations for the ${\beta}$ and ${\alpha}$ phases are carried out at several temperatures and the radial distribution functions (rdf) are obtained at those temperatures in the (N, V, E) ensemble. But the phase transition is not found in our calculation. Next the phase transition is studied with the (N, P, T) MD and we find some evidences of phase transition. At 3 Kbars and 2 Kbars the phase transition temperatu re is about 300 K. For 3.55 Kbars, the phase transition is higher (420 K) than the low pressure case. The phase transition temperature is somewhat dependent on the pressure in our calculations.

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Ferroelectric Phase Transition of Lead Free (1-x)(Na0.5K0.5)NbO3-xLiNbO3 Ceramics

  • Park, Jong-Ho;Park, Hui-Jin;Choi, Byung-Chun
    • Transactions on Electrical and Electronic Materials
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    • v.13 no.6
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    • pp.297-300
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    • 2012
  • Lead-free (1-x)$(Na_{0.5}K_{0.5})NbO_3-xLiNbO_3$, i.e., NKN-LNx (x=0.0, 0.1, 0.2, 0.3, 0.4 mol) was prepared using the conventional solid state reaction method. The effects of LN mixing on the ferroelectric properties of NKN-LNx ceramics were studied using a dielectric constant and P-E (Polarization-electric field) measurements. Ferroelectricity was observed in the composition for x approximately varying between 0.0 and 0.4. Minimum remanent polarization $2P_r=5C/cm^2$ was achieved in the composition for x = 0.2. The ferroelectric phase transition temperature $T_C$ increased with increasing LN content. The ferroelectric phase transition of NKN-LNx ($x{\geq}0.1$) is a second-order phase transition, and that of NKN-LNx ($x{\leq}0.2$) is a first-order phase transition. These results indicate that the ferroelectric phase transition temperature of NKN-LNx change from that of second-order to weak first-order phase transition according to the LN content.

Electric Field-Induced Phase Transition Behavior in Tetragonal Pb(Zn1/3Nb2/3)O3-PbTiO3 Single Crystals

  • Jeong, Dae-Yong;Kim, Jin-Sang;Kim, Hyun-Jai;Yoon, Seok-Jin
    • Journal of the Korean Ceramic Society
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    • v.43 no.7
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    • pp.389-392
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    • 2006
  • Electric field-induced phase transition from the tetragonal to rhombohedral phase was investigated for the <111> direction in tetragonal PZN-PT single crystals, which have spontaneous polarization along the <001> direction. From the strain and dielectric data, it was confirmed that the samples followed a tetragonal-orthorhombic-rhombohedral phase transition sequence with application of an electric field. This transition is different from the rhombohedral-tetragonal phase transition of <001> rhombohedral composition single crystals, in which a phase transition occurred without showing the intermediate orthorhombic phase.

The Effect of Salt and pH on the Phase Transition Behaviors of pH and Temperature-Responsive Poly(N,N-diethylacrylamide-co-methylacrylic acid)

  • Liu, Tonghuan;Fang, Jian;Zhang, Yaping;Zeng, Zhengzhi
    • Macromolecular Research
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    • v.16 no.8
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    • pp.670-675
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    • 2008
  • A series of pH and temperature-responsive (N,N-diethylacrylamide-co-methylacrylic acid) copolymers were synthesized by radical copolymerization and characterized by elemental analysis, Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR) $^1H$, $^{13}C$ and LLS. The effects of salt and pH on the phase transition behaviors of the copolymers were investigated by uv. With increasing NaCl concentration, significant salt effects on their phase transition behaviors were observed. UV spectroscopic studies showed that the phase transition became faster with increasing NaCl concentration. In addition, the phase transition behaviors of copolymers were sensitive to pH. The pH and temperature sensitivity of these copolymers would make an interesting drug delivery system.

Velume Phase Transition of Poly (N-isopropylacrylamide-co-sodium methacrylate) Hydrogel Crosslinked with Poly(ethylene glycol) diacrylate (Poly(ethylene glyco1) diacrylate로 가교된 Poly(N-isopropylacrylamide) Hydrogel의 부피 상전이 특성)

  • 김선아;한영아;손성옥;지병철
    • Polymer(Korea)
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    • v.26 no.5
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    • pp.653-660
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    • 2002
  • The volume phase transition of poly(N-isopropylacrylamide) (PNIPAAm) and poly (N-isopropylacrylamide-co-sodium methacrylate) (P (NIPAAm-co-SMA)) hydrogels crosslinked with poly (ethylene glycol) diacrylate (PEGDA) was investigated in consideration of water content and surface area. The volume phase transition temperature of hydrogel was not affected by the concentration of crosslinking agent, which increased over 40$\^{C}$ by incorporating a small amount of SMA. Higher volume phase transition temperature was obtained when PEGAD was used as a crosslinking agent, suggesting that the chain length of crosslinking agent had a significant effect on the volume phase transition temperature. The surface area of PNIPAAm and P (NIPAAm-co-SMA) gels fell off around the volume phase transition temperature, resulting from the fact that the size of pores reduced remarkably in the course of the volume phase transition. Hence, the surface area and the pore size were considered to be important factors indicating the volume phase transition.

OPTIMAL CONTROL OF GLOBAL PRESS FOR AN ADSORBATE-INDUCED PHASE TRANSITION MODEL

  • Ryu, Sang-Uk
    • Journal of the Chungcheong Mathematical Society
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    • v.21 no.4
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    • pp.543-553
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    • 2008
  • This paper is concerned with the optimal control problem of global press for an adsorbate-induced phase transition model. That is, we show the existence of the optimal control and derive the optimality conditions. Moreover, we obtain the uniqueness of the optimal control.

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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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Nanoscopic Understanding of Phase Transition of Epitaxial VO2 Thin Films (에피택셜 VO2 박막의 상전이에 대한 미시적 이해)

  • Kim, Dong-Wook;Sohn, Ahrum
    • Journal of the Korean institute of surface engineering
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    • v.50 no.3
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    • pp.141-146
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    • 2017
  • We investigated configuration of metallic and insulating domains in $VO_2$ thin films, while spanning metal-insulator phase transition. Kelvin probe force microscopy, of which spatial resolution is less than 100 nm, enables us to measure local work function (WF) at the sample surface. The WF of $VO_2$ thin films decreased (increased) as increasing (decreasing) the sample temperature, during the phase transition. The higher and lower WF regions corresponded to the insulating and metallic domains, respectively. The metallic fraction, estimated from the WF maps, well explained the temperature-dependent resistivity based on the percolation model. The WF mapping also showed us how the structural defects affected the phase transition behaviors.

On the strong attractive force dependence of the surface phase transition : Qualitative consideration from the occupation statistics (표면상변이의 강인력 의존성 : 점유통계를 이용한 정성적 고찰)

  • 김철호
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.7 no.4
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    • pp.573-577
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    • 1997
  • Surface phase transition is known to be observed at the system that there exists a strong attractive potential between particles adsorbed. This study presents a dependence of the surface phase transition on strong attractive force using a simple occupation statistical method. It was found that the system exhibits a phase transition from the vacuum phase into the population phase and the critical pressure also increases with the temperature. This fact indicates that these results explain well qualitatively the surface phase transition.

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Molecular Dynamic Simulations of the Phase Transition of $\alpha-quartz$ and $\alpha-quartz-type$-type $GeO_2$ under High Pressure (고압력하에서의 $\alpha-quartz$$\alpha-quartz$$GeO_2$의 상전이에 관한 분자동력학시뮬레이션)

  • ;;;;河村雄;Zenbe-e Nakagawa
    • Journal of the Korean Ceramic Society
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    • v.34 no.7
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    • pp.713-721
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    • 1997
  • Molecular dynamic (MD) simulations with new interatomic potential function including the covalent bond were performed on the phase transition of $\alpha$-quartz-type GeO2 under high pressure. The optimized crystal structure and the pressure dependence of the lattice constant showed higher reproducibility than the previous models and were in very good agreement with the experimental data. A phase transition of $\alpha$-quartz and $\alpha$-quartz-type GeO2 by simulation was found approximately 24 GPa and 6-7 GPa, respectively. This phase transition involved an abrupt volume shrinkage and showed 4-6 coordination mixed structure with the increasing in the coordination number of cation.

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