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김재형,이광세,김정배 인제대학교 1992 仁濟論叢 Vol.8 No.2
Ferroelectric Pb5Ge3011 single crystal was grown from the melt by the Czochra1ski method. From the complex dielectric measurements and the pyroelectric measurements, it was confirmed that Pb5Ge3011 undergoes a displacive second order phase transition at 177 ℃. Arrehnius' activation energy was estimated as 1.2eV from the measurements of electric conductivities. Refractive indices obtained by using the Brewster's law are no=2.111, ne=2.140for λ=6328Å at room temperature and thermo-optical coefficients are 4.26×10-5/℃ in the ferroelectric phase and 2.71×10-5/℃in the paraelectric phase. An impedance relaxation was observed over a wide temperature range, including the Curie temperature. The relaxation was composed of two mechanisms, the one due to a charge carrier hopping Process and the other one resulting from the intrinsic polarization of the ferroelectric material.
Raman Spectra of Paraelectric NH₄H₂PO₄Crystal
Lee, Kwang-Sei,Kim, Jae-Hyung 인제대학교 1989 仁濟論叢 Vol.5 No.1
NH4H2PO4 단결정의 상유전상에서의 라만 활성 모우드를 광산란 실험으로 조사하였다. 이때 파수범위는 10-3600cm-1 이고, 실온에서 측정하였다. 라만 스펙트럼을 분석하므로써, 양성자 진동, 가로광학 포논, 내부진동, O-H-O 진동을 분류하여 진동 대칭성을 결정하였다. Light scattering measurements of the Raman active modes of vibration in the range 10-3600 cm-1 are reported for the paraelectric phase of NH4H2PO4 at room temperature. Through examination of these spectra we have identified the protonic, transverse optic, internal, and O-H-O valence vibrations and determined their symmetries.
High-Temperature Phase Transformation in Ferroelectric LiH3(SeO3)2 and Topochemical Nature
Kwang-Sei Lee,Jin Soo Kim,Jeong-Bae Kim 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The high-temperature anomalies of LiH3(SeO3)2 were optically studied in the rst heating process. Optical observation shows an appreciable change of surface, revealing some kind of viscous liquid ow at the surface. The sample history is very important for the high-temperature properties. Phase transformations are actually due to changes in the conditions at the surface. The conditions under which a sample is prepared at room temperature can affect the temperature at which a phase transformation occurs when the sample is heated. The wide scatter of the transformation temperature indicates that the nature of the high-temperature anomaly is obeyed by the topochemical factors, i:e:, controlled by the defect structures at the surface of crystals. The temperature 75-90 C (Tp1) is interpreted as an onset of partial melting related to thermal decomposition at reaction sites at or near the surface of solids. The physicochemical state above Tp1, at least on the surface, is regarded as a transitory liquid one that is, with multi-component, consisting of unreacted remaining ferroelectric LiH3(SeO3)2 and reacted intermediate products, neither being the hypothetical paraelectric phase or being the molten state of LiH3(SeO3)2 itself. The surface layer formed between bulk and electrode may result in space charge and aect severely the apparent capacitance and conductance of the specimen, which is the origin of the very large values of dielectric constant and electrical conductivity above Tp1.
Three-month Treatment Response and Exacerbation in Chronic Obstructive Pulmonary Disease
Lee, Jung Su,Rhee, Chin Kook,Yoo, Kwang Ha,Lee, Ji-Hyun,Yoon, Ho Il,Kim, Tae-Hyung,Kim, Woo Jin,Lee, JinHwa,Lim, Seong Yong,Park, Tai Sun,Lee, Jae Seung,Lee, Sei Won,Lee, Sang-Do,Oh, Yeon-Mok The Korean Academy of Medical Sciences 2015 JOURNAL OF KOREAN MEDICAL SCIENCE Vol.30 No.1
Antiferroelectric Phase Transition of NH?H?(PO?)?-?(A?O?)? Mixed Crystals
Lee, kwang-Sei,Kim, Jae-Hyung 인제대학교 1988 仁濟論叢 Vol.4 No.1
반강유전체인 NH4H2PO4(ADP)와 NH4H2AsO2(ADA)간의 고용체의 상전이 현상에 대한 유전상수 측정결과, 고용체의 상전이 온도는 순수한 두 결정의 상전이 온도 사이에 있으며 강한 일차 상전이가 유지됨을 관측하였다. The solid solutions between two different KH2PO4- type antiferroelectrics were studied by dielectric constant measurements. The transition temperature was found to fall between the temperatures of the end components and a strong first-order transition was retained.
Raman Scattering Study of Ferroelastic Pb3(PO4)2 at High Pressures
Kwang-Sei Lee,Y.S. Yu,Sung-Hwan Eom 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
Pb3(PO4)2 undergoes a frst-order ferroelastic phase transition at about Tc = 180C between a high-temperature (HT) trigonal (rhombohedral) phase (space group R3m D5 3d) and a lowtemperature (LT) monoclinic phase (space group C2=c C6 2h). An earlier Raman scattering study for high-pressure phase transition of Pb3(PO4)2 has been reported only to 3.5 GPa. In this work, we extended the pressure domain up to 9 GPa by Raman scattering in order to search for new phases and throw some light on the nature of the high-pressure phase transition. The Raman spectra showed a high-pressure transition at about 2.0 GPa and did not reveal any additional signifcant change of vibrational modes above 2.0 GPa, indicating the persistence of the trigonal phase up to 9 GPa. By combining the previously reported results of neutron, X-ray and Raman experiments with the present Raman results, phase diagrams of Pb3(PO4)2 are constructed. Linear extrapolation of experimentally observed dTc=dp indicates transition pressure 5 GPa at absolute zero, as plotted. However, quantum uctuation at low temperatures may induce the bowing of dTc=dp, not yet experimentally found. Then Pb3(PO4)2 may be a `quantum paraelastic' or `incipient ferroelastic' at low temperatures just like a `quantum paraelectric' or `incipient ferroelectric'.
Surface Transformation of Ferroelectric LiH3(SeO$_3$)$_2$ and Topochemical Nature
Kwang-Sei Lee,Jin Soo Kim,Yun-Sik Yu 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
The high-temperature phenomenon of ferroelectric LiH3(SeO3)2 was studied by thermal analyses and impedance spectroscopy. Dierential scanning calorimetry reveals an anomalous increase at about 70 C in agreement with thermogravimetry and a peak at 114 C. Dielectric constant and electrical conductivity show an anomaly at about 87 C and 105 C. The large and irreversible thermal hysteresis in dielectric constant and electrical conductivity is interpreted in terms of proton transport and thermal decomposition. Optical observation showed a drastic surface transformation. Present study indicates that the high temperature anomaly around Td is controlled by topochemical factors.
Raman Scattering Study of LiH2PO4
Kwang-Sei Lee,고재현,V.H. Schmidt 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
The structural evolution of polycrystalline LiH2PO4 has been studied between room temperature and 13 K by using dielectric measurement and Raman-scattering study. No signicant change is observed over the temperature range, indicating that the room-temperature orthogonal phase persists to 13 K. Assignments of vibrational modes are qualitatively proposed: low-frequency (0 300 cm1) external modes and high-frequency (300- 4000 cm1) internal modes. In addition to the internal modes of PO4 tetrahedra, the internal modes of LiO4 are spectroscopically found. This is a peculiar structural aspect of LiH2PO4, compared to other MX2RO4-type (M = K, Rb, Cs, NH4,Tl; X = H, D; R = P, As) crystals without MO4 tetrahedra. The modes in the frequency rangeof 390-500 cmက1 are assigned as the internal modes of LiO4. This frequency range overlaps with those of 2(PO4) and 4(PO4), and may complicate the assignment of internal modes of LiH2PO4. The LiO4 tetrahedron shares oxygens with the four neighbor PO4 tetrahedra. The frequencies of O-H vibration of LiH2PO4 indicate that there are two types of hydrogen bonds, including an intermediate one and a strong one.
An UltraWideBand BALUN on Thin Film Substrate using MCM-D Technology
Chan-Sei Yoo,Ji-Min Maeng,Sang-Sub Song,Kwang-Hoon Lee,Jae-Hyun Yoon,Dongsu Kim,Hee-Seok Lee,Woo-Sung Lee,Kwang-Seok Seo 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
This paper presents a integrated balun using MCM-D technology for UWB application(3.1∼4.8 ㎓). Two types of circuit was suggested and compared. The first one using distributed circuit shows good power diving but poor phase shifting. On the other hand, the balun using lumped circuit shows good phase shifting but poor power dividing. To get good performance in both region, that is power dividing and phase shifting, the circuit using lumped and distributed one together was suggested and evaluated on the silicon substrate. Finally, the suggested balun shows good power imbalance(2 ㏈) and phase imbalance(10°). That can be integrated with the chipset using BEOL(back end of line) process.