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Light Scattering Study of Glass Transition Temperatures of Glucose-Water Mixtures
서정아,오지영,김형국,황윤회 부산대학교 유전체물성연구소 2004 유전체 논문집 Vol.3 No.
We studied glass transition temperatures of glucose-water mixtures by using Brillouin light scattering. We fitted the polarized components of the Brillouin spectra measured by backscattering geometry to simple Lorentzian form and estimated the glass transition temperature from the slope of the temperature-dependent Brillouin peak shift.
Binding Energy of Oxigen and Methane Adsorbed on Bundles of Open-Ended Single-Wall Carbon Nanotubes
서주연,유대황,곽진성,황윤회,김형국 부산대학교 유전체물성연구소 2004 유전체 논문집 Vol.3 No.
The adsorption of oxygen and methane on the bundles of open-ended single wall carbon nanotube(SWNT) was studied using the volumetric adsorption qst was obtained from the adsorption isotherm measurements performed at different temperatures. The trend in the values of the methane isosteric heat of adsorption showed three regions, representative of the adsorption on the different types of adsorption sites. In case of oxygen, on the other hand, such distinguishable regions were not appeared in the N-qst graph. From the results of qst the binding energies of oxygen and methane adsorbed on open-ended SWITs were estimated.
Dielectric properties of the near stochiometric KLN crystal in the ferroelectric Curie range
Yoon-Hwae Hwang,Byeong-Eog Jun,Chungsik Kim,Dong-Jin Kim,Hyung-Kook Kim,Jung-Nam Kim 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The dielectric constants of near-stoichiometric potassium lithium niobate (K2:83Li1:84Nb5:33O15:66 , KLN43) crystal in the frequency range from 100 Hz to 1 MHz showed a dielectric anomaly at maximum temperatures around Tmax = 510 C. At low frequencies, ranging from 100 Hz to 10 kHz, the dielectric maximum temperature Tmax shifted to higher temperature as the frequency increased in the Curie range. The impedance Cole-Cole plot in the Curie range could betted by the complex nonlinear least squares (CNLS) method with two parallel Rcircuits in series: Z(!) = R1=[1 + (i!)n11]+R2=[1 + (i!)n22], where 1 and 2 are the relaxation times,1;2 = R1;2C1;2. The universal capacitance Ce= C(i!)n1 was applied for each RCecircuit. This observation suggests that the universal dynamic response of KLN43 crystal in the Curie rangewas the superposition of the low-frequency dispersion (LFD) due to the mobile charge carriers and to the rotational dielectric relaxation mechanism in the dipolar regions.
The Ionic Conduction and Dielectric Properties of Pure and Na-Doped K3Li2..xNb5+xO15+2x Crystals
전병억,Yoon-Hwae Hwang,Chung Sik Kim,Dong Jin Kim,Gwang Soo Jeen,Hyung Kook Kim,Jung Nam Kim,Suk Chul Song 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Pure and Na-doped potassium lithium niobates (KLN) crystals were grown by r.f. heating Czochralski method from the melts composition Na2O : K2O : Li2O : Nb2O5 = x : 32 - x : 25 : 43 (x = 0, 2 mol%). Tetragonal cell volume of the Na-doped KLN crystal decreases compare to the pure KLN, because K+ ions in the A1 sites were partially replaced by Na+ ions. The ferroelectric phase transition was observed from the dielectric properties along the polar c-axis of pure and Na-doped KLN crystals. The Curie temperature of pure and Na-doped KLN were 502 C and 456 C, respectively. Both KLN crystals showed the strong low frequency dielectric dispersion at about phase transition temperatures in the frequency range of 100 Hz 10 kHz. The ac conductivity showed a slope change at the Curie temperature in the Arrhenius plot of log(kBT33) vs. 103=T . The electrical conduction in pure and Na-doped KLN crystals originates mainly from the ionic hopping. The Li+ ions in A1 sites are considered to be the main charge carriers. The activation energy at lower temperature of pure and Na-dope KLN were 0.83 eV and 0.72 eV, respectively.
Jeong, Hyewon,Yoon, Sinmyung,Kim, Jung Hwa,Kwak, Do-Hyun,Gu, Da Hwi,Heo, Seung Hwae,Kim, Hyunhong,Park, Sangmin,Ban, Hyeong Woo,Park, Jongnam,Lee, Zonghoon,Lee, Jong-Soo,An, Kwangjin,Son, Jae Sung American Chemical Society 2017 Chemistry of materials Vol.29 No.24
<P>We report a new family of inorganic ligands, namely, transition metal-based thiometallates, for the surface functionalization of colloidal nanocrystals (NCs). We synthesized Pt-, Fe-, Co-, and Ni-based thiometallates, in which transition metal ions were complexed with polysulfides. These inorganic anions easily exchanged the surface organic ligands of various nanocrystals of metal, semiconductor, and oxide materials, without affecting the NCs’ primary structural and optical characteristics. Furthermore, upon heating, these complexes were decomposed and transformed into crystalline phases of metal sulfides or pure metals, accompanied by the evaporation of S. Based on this effect, we selectively synthesized homogeneously distributed atomic Pt clusters or Pt nanoparticles on Fe<SUB>3</SUB>O<SUB>4</SUB> nanomaterials by heating thioplatinate-capped Fe<SUB>3</SUB>O<SUB>4</SUB> NCs. As a model application, we tested the prepared Pt-functionalized Fe<SUB>3</SUB>O<SUB>4</SUB> nanomaterial as a heterogeneous catalyst for CO oxidation reaction and Pt–Fe<SUB>3</SUB>O<SUB>4</SUB> catalysts exhibited the high turnover frequency due to the homogeneous distribution of atomic Pt over Fe<SUB>3</SUB>O<SUB>4</SUB> and the corresponding strong metal–support interaction. This approach opens up a new avenue to functionalize nanocrystals for catalytic applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2017/cmatex.2017.29.issue-24/acs.chemmater.7b04387/production/images/medium/cm-2017-04387v_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm7b04387'>ACS Electronic Supporting Info</A></P>
Sound Propagation in 5CB Liquid Crystals Homogeneously Confined in a Planar Cell
Ko, Jae-Hyeon,Hwang, Yoon-Hwae,Kim, Jong-Hyun The Korean Infomation Display Society 2009 Journal of information display Vol.10 No.2
The Brillouin spectrum of 4'-n-pentyl-4-cyano-biphenyl (5CB) liquid crystals homogeneously confined in a planar liquid crystal (LC) cell was measured using a 6-pass tandem Fabry-Perot interferometer. By adopting a special right-angle scattering geometry, the sound velocity of 5CB was estimated from the Brillouin shift without knowing the refractive index. The sound velocity of the longitudinal wave propagating along the direction of the directors aligned parallel to the glass plates of the LC cell was 1784${\pm}$7 m/s at 300 K. The attenuation coefficient $\alpha$ was estimated to be approximately $1.9{\times}10^6m^{-1}$, which is about twice as large as that of the longitudinal sound wave propagating along the direction perpendicular to the directors. The present method may be very useful in the evaluation of the elastic properties of the materials used in display devices, whose refractive indices are not known.
XPS studies of the ferroelectric potassium lithium niobate crystal
Byeong-Eog Jun,Yoon-Hwae Hwang,Chung-Sik Kim,Hyung-Kook Kim,Jong-suk Chae,Jung-Nam Kim 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Ar+-ion-sputtered surface of KLN crystal was studied by X-ray photoelectron spectroscopy in order to investigate the oxidation states and chemical environments of K, Li, Nb and O ions. As Ar+-sputtering time increased, the decreasing binding energy of Nb 3d and the peak broadening of mixed Nb 4s and Li 1s (namely Nb* 4s) levels were observed. Also, the binding-energy dierence between O 1s and Nb* 4s increased as Ar+-ion-sputtering time increased. The broad peak of Nb* 4s was considered to be related to the site occupancy of Li ion in A1 and C in tetragonal tungsten-bronze structure.
Dielectric Study on The Secondary Relaxation in Glucose-Water Mixtures
ji young oh,Yoon-hwae hwang,Hyung Kook Kim,Jeong-Ah Seo,Seiji Kojima 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.44 No.32
We have studied two types of relaxation phenomena, the and the secondary relaxations, in the glucose-water mixtures by applying frequency-dependent dielectric constant measurement. Dielectric measurements of 5 % and 10 % glucose-water mixtures were performed in the frequency range of 0.1 Hz-10 MHz and in the temperature range of 260-320 K. The addition of water to glucose is believed to enhance the contribution of the secondary relaxation.