19F NMR Study of Fluorinated High Tc Superconductor YBa₂Cu₃OxF

Lee,Moohee 建國大學校基礎科學硏究所 1999 理學論集 Vol.24 No.-

YBCO 고온 초전도체에 불소를 치환한 YBa₂Cu₃OxF(x~6) 분말시료를 고온고상법으로 제조하고, 그 특성을 핵자기 공명실험과 핵사중극 공명실험으로 측정 분석하였다. 시료중 하나에 대한 핵자기 공명 결과, 불소원자가 85%까지 단일상으로 치환된 것으로 판명되었다. NMR 스핀-격자 완화율은 Korringa 온도 의존성을 보였는데 이것은 불소가 미약하지만 금속상태로 도입되었음 입증한다. 중성자 실험과 핵자기 공명실험 결과를 종합하여 분석하면, 불소가 사면체의 꼭지점에 있는 산소를 치환해 들어 간 것으로 보여진다. Polycrystalline samples of fluorinated high Tc superconductor with nominal composition YBa₂Cu₃OxF(x~6) (YBaCuOF) were prepared by solid state reaction techniques and studied by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. NMR results on one of YBaCuOF samples showed that 85% of the expected amount of fluorine was incorporated into a single phase. Korringa temperature dependence of NMR spin-lattice relaxation was observed in the normal state indicating that the fluorine is in a weak metallic environment. Analysis of neutron scattering indicates that the fluorine must substitute for oxygen and this result, combined with the NMR results, suggests that the fluorine is most likely substitutued for the apical oxygen site.

Orientation of a MgB2 Powder in a Magnetic Field

Lee, Moohee,Kang, Kihyeok,Mean, B. J.,Kim, Sung Hoon,Ndiaye, B.,Kim, J. Y.,Cho, B. K. Korean Physical Society 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6

19F NMR Study of Fluorinated High Tc Superconductor La Sr CuCo(O F)₄

Lee,Moohee 建國大學校基礎科學硏究所 1999 理學論集 Vol.24 No.-

불소를 치환한 (LaSrCuOF) 분말시료를 고온고상법으로 제조하고, 그 특성을 핵자기 공명실험으로 측정 분석하였다. ?? 핵자기 공명 결과, 불소원자가 65%까지 단일상으로 치환된 것으로 판명되었다. NMR 스핀-격자 완화율은 Korringa 온도 의존성을 보였는데, 이것은 불소가 미약하지만 금속상태로 도입되었음을 입증한다. 핵자기 공명실험과 X-ray 회절측정을 분석한 결과, 불소가 육면체의 꼭지점에 있는 산소를 치환해 들어 간 것으로 보여진다. Polycrystalline samples of fluorinated high Tc superconductor with nominal compositions (LaSrCuOF) were prepared by solid state reaction techniques and studied by pulsed nuclear magnetic resonance (NMR) measurements. NMR results on the sample showed that 65% of the expected amount of fluorine was incorporated in a single phase which became superconducting at 37 K. Korringa temperature dependence of spin-lattice relaxation time T₁ was observed in the normal state of LaSrCuOF suggesting that fluorine is in a weak metallic environment. Analysis of NMR data and X-ray diffraction experiments suggests that the substitutional site of fluorine is most likely the apical oxygen site.

1H NMR Measurements of the Phase Transition of (NH₄)₃H(SO₄)₂ Single Crystals

S. H. Choi,Moohee Lee,Ae Ran Lim,K. S. Han,S. K. Kwon,S. K. Nam 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

$^1$H nuclear magnetic resonance (NMR) experiments have been performed in the temperature range of 30 -- 300 K at 7 T to investigate the phase-dependent nature of the dynamic network of hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The crystal has six phases, which are ferroelectric, antiferroelectric, incommensurate, antiferroelectric, ferroelastic, and superionic with the respective transition temperatures of 63, 133, 139, 256 and 413 K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar for the ammonium protons and the hydrogen-bond protons over the entire range of experimental temperatures. The T₁, of ¹H NMR gradually decreases down to 120 K and starts to steeply increase below 100 K. Then, the T₁ shows an abrupt decrease below 68 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. The ¹H NMR spectrum shifts to the high-frequency side at temperatures below 63 K due to the ferroelectric phase transition. This behavior of the T₁ and the spectrum confirms a dramatic change in the dynamics of hydrogen bonds associated with the ferroelectric phase transition at 63 K. $^1$H nuclear magnetic resonance (NMR) experiments have been performed in the temperature range of 30 -- 300 K at 7 T to investigate the phase-dependent nature of the dynamic network of hydrogen bonds in a ((NH₄)₃H(SO₄)₂ single crystal. The crystal has six phases, which are ferroelectric, antiferroelectric, incommensurate, antiferroelectric, ferroelastic, and superionic with the respective transition temperatures of 63, 133, 139, 256 and 413 K. The spin-lattice relaxation time, T₁, of ¹H NMR is similar for the ammonium protons and the hydrogen-bond protons over the entire range of experimental temperatures. The T₁, of ¹H NMR gradually decreases down to 120 K and starts to steeply increase below 100 K. Then, the T₁ shows an abrupt decrease below 68 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. The ¹H NMR spectrum shifts to the high-frequency side at temperatures below 63 K due to the ferroelectric phase transition. This behavior of the T₁ and the spectrum confirms a dramatic change in the dynamics of hydrogen bonds associated with the ferroelectric phase transition at 63 K.

¹¹B NMR Study of the Spin Structure and Dynamics in TbB4 Single Crystals

S. K. Kwon,Moohee Lee,B. J. Mean,S. H. Choi,S. K. Nam,조병기 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

¹¹B nuclear magnetic resonance (NMR) measurements have been performed on single crystals of TbB₄ to investigate the 4f spin structure and dynamics. ¹¹B NMR spectrum and shift, as well as the spin-lattice and the spin-spin relaxation rates, have been measured down to 5 K at 8 T perpendicular to the (110) plane. ¹¹B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments of Tb. In addition, both are proportional to the magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below TN = 43 K, the single broad resonance peak of ¹¹B NMR splits into several peaks reflecting the onset of internal magnetic fields due to the antiferromagnetic spin arrangements. Assuming that the 4f moments are aligned antiferromagnetically and collinearly in the basal plane perpendicular to the c-axis, we have calculated the dipolar fields at the 16 boron nuclear sites from the 4f spins of Tb. The results show that the various peaks of the ¹¹B NMR spectrum at 5 K are generally consistent with the calculation, confirming that the collinear spin arrangement is correct. The longitudinal and the transverse relaxation rates, 1/T₁ and 1/T₂, are independent of temperature above TN, but decrease tremendously below TN, indicating a huge suppression of the spin fluctuations. ¹¹B nuclear magnetic resonance (NMR) measurements have been performed on single crystals of TbB₄ to investigate the 4f spin structure and dynamics. ¹¹B NMR spectrum and shift, as well as the spin-lattice and the spin-spin relaxation rates, have been measured down to 5 K at 8 T perpendicular to the (110) plane. ¹¹B NMR shift and linewidth are huge and strongly temperature-dependent due to the 4f moments of Tb. In addition, both are proportional to the magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below TN = 43 K, the single broad resonance peak of ¹¹B NMR splits into several peaks reflecting the onset of internal magnetic fields due to the antiferromagnetic spin arrangements. Assuming that the 4f moments are aligned antiferromagnetically and collinearly in the basal plane perpendicular to the c-axis, we have calculated the dipolar fields at the 16 boron nuclear sites from the 4f spins of Tb. The results show that the various peaks of the ¹¹B NMR spectrum at 5 K are generally consistent with the calculation, confirming that the collinear spin arrangement is correct. The longitudinal and the transverse relaxation rates, 1/T₁ and 1/T₂, are independent of temperature above TN, but decrease tremendously below TN, indicating a huge suppression of the spin fluctuations.

195Pt NMR Study of the Influence of Nafion Ionomer on the Enhanced Local Density of States at the Surface of Carbon-Supported Pt Catalysts

Kee Sung Han,Moohee Lee 한국자기공명학회 2009 Journal of the Korean Magnetic Resonance Society Vol.13 No.2

195Pt NMR measurements were performed to deduce the variation of local density of states at the Fermi energy (EF-LDOS) at the surface of carbon-supported Pt catalysts due to the addition of Nafion® ionomer in the metal-electrode-assembly for fuel cells. The results showed that the EF-LDOS at the surface of Pt particles was enhanced by the addition of Nafion® ionomers whereas it was uninfluenced in the inner (bulk) part of the Pt particles. This suggests that the effects of ionomers on the electronic states of the Pt particle surface are related to the electrochemical activity of the catalysts.

포항 분지 제3기층 시추코아 유기물의 석유 지화학적 특성

이영주,곽영훈,윤혜수,정태진,오재호,김학주,강무희,Lee Youngjoo,Kwak Young Hoon,Yun Hye Su,Cheong Tae Jin,Oh Jae Ho,Kim Hagju,Kang Moohee 한국석유지질학회 1997 한국석유지질학회지 Vol.5 No.1

포항 분지 신제3기 연일층군 퇴적물내 유기물의 석유 지화학적 특성연구를 위하여 시추공 B, E, F, H에서 이암 시추 시료를 채취하여 유기탄소 분석, Rock-Eval 열분석을 실시하였다. 또한 각 시추공의 선별된 시료에 대해서 케로젠을 분리하고 비투멘을 추출하여 광학 현미경 관찰, 적외선 분광 분석, 생물표기화합물 분석을 실시하였다 시추공 시료의 유기탄소 함량은 $0.55{\~}3.74{\%}$로 석유 근원암의 조건을 갖추었고 석유 생성 잠재력을 나타내는 S1+S2 값은 H공을 제외한 거의 모든 시료에서 각각 2mgHC/gRock 이상을 나타내어 시추공 시료의 유기물 함량 및 유기물의 석유 생성 잠재력은 대체로 양호한 것으로 나타났다. Rock-Eval 열분석, 적외선 분광 분석 및 케로젠의 현미경 관찰을 통해서 살펴본 B, E, F 시추시료의 유기물은 타이프 II에 비교되었고 H공의 시료는 육성 기원 유기물이 우세해서 타이프 III에 비교되었다 H공 시료의 유기물이 다른 시추공 시료의 그것에 비해 석유 생성 잠재력이 상대적으로 낮은데 이는 분지의 가장자리에 위치하여 육성 유기물의 함량이 상대적으로 많은데 기인하는 것으로 해석된다. 연일층군 유기물의 열 성숙도는 미성숙 단계이고 시추 심도에 따른 뚜렷한 열적 진화 양상을 나타내지 않았다. 석유 지화학적 분석 자료를 종합하면 포항 분지 연일층군은 유기탄소의 함량 및 석유 생성 잠재력은 양호하지만 열적으로 미성숙 상태라서 아직 석유 생성 단계에 이르지 못하였는데 이는 주로 퇴적층의 매몰 심도가 얕은 것에 기인하는 것으로 판단된다. 케로젠의 현미경 관찰 결과와 생물표기화합물 분석에 의하면 연일층군 유기물은 주로 해양기원 유기물로 구성되어 있으나 육상 기원 유기물도 상당히 포함되어 있었으며, 프리스테인/파이테인의 비율을 고려 할 때 환원 환경하에서 퇴적된 것으로 보인다. 이런 퇴적 환경 및 유기물 특징을 고려했을 때 포항 분지는 육지에서 가까운 바다로 주변 육상 기원 유기물의 유입이 용이했던 것으로 여겨진다. 시추공 분석 시료의 최하부 구간에는 육상 기원 유기물이 우세한데 이는 포항 분지 초기의 육성 퇴적 환경의 영향에 의한 것으로 해석된다. Core samples from the B, E, F, H wells in the Tertiary Pohang Basin were analysed for total organic carbon (TOC) content and subject to Rock-Eval pyrolysis in order to assess petroleum geochemical characteristics of organic matter. Following geochemical screening, we selected samples from each well for the study of bitumen and kerogens such as optical observation, infra-red spectroscopy and biomarker analyses. Sediments of the Tertiary Yonil Group contain total organic carbon ranging from $0.55{\%} to 3.74{\%}$ with S1+S2 values higher than 2mgHC/g Rock in B, E and F wells, which indicates fair hydrocarbon generation potential. Most organic matter in the B, E, F wells is compared to type II based on the Rock-Eval pyrolysis, infra-red spectroscopy and optical observation. However, organic matter in the H well is compared to type III because the well is located at the margin of the basin where the preservation of terrestrial material is dominant. Geochemical analyses show that organic matter in the Yonil Group is thermally immature although thermal maturity slightly increases with depth. Maturity levels of the extracted kerogens are similar to those of bulk samples ($Tmax<435^{\circ}C$. Petroleum geochemical charateristics of the sediments in the Tertairy Yonil Group is fair in terms of the organic richness and hydrocarbon genetic potential, but organic matter is thermally immature due to the shallow burial depth. Optical observation of the kerogens and biomarker analysis show that organic matter in the Yonil Group is both marine and terrestrial origin, although it was deposited in marine environment. Pristane/phytane ratio suggests rather anoxic depositional environment. Transitional characteristics of organic matter indicate that the marine Yonil Group was deposited near the terrestrial environments. Input of terrestrial organic matter is more prevalent in the samples recovered from the lowermost horizon in the wells due to the terrestrial environment at the time of basin formation.

1H Nuclear Magnetic Resonance study of Ferroelectric (NH4)3H(SO4)2

S. H. Choi,K. S. Han,S. K. Kwon,S. K. Nam,H. H. Choi,Moohee Lee,Ae Ran Lim 한국자기공명학회 2007 Journal of the Korean Magnetic Resonance Society Vol.11 No.2

1H nuclear magnetic resonance (NMR) experiments have been performed at 30 - 300 K and 7 T to investigate dynamics of hydrogen bond network in the single crystal (NH4)3H(SO4)2. The two proton sites, ammonium proton and hydrogen-bond proton, are identified from the 1H NMR MAS spectrum at 340 K. As temperature decreases, the 1H NMR spectrum shifts to the higher frequency side with a larger linewidth. The spectrum at 65 K shows a distinctive change in line shape toward the ferroelectric transition at 63 K. The measured values of T1 for ammonium and hydrogen-bond protons are similar in the whole range of temperature. T1 of 1H NMR shows a gradual decrease down to 120 K and starts to steeply increase below 100 K. Then T1 shows abrupt decrease below 70 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. This temperature dependence of spectrum and T1 clearly prove that the large change in the dynamics of hydrogen bond network is associated with the ferroelectric phase transition at 63 K.