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고재현,신선협,장문규,원충재,허남정 한국물리학회 2018 Current Applied Physics Vol.18 No.1
The acoustic behaviors of oxygen-reduced barium titanate (BaTiO3-d) single crystals with d~0.04 were investigated as a function of temperature by using Brillouin spectroscopy. The longitudinal acoustic mode of the moderately-reduced BaTiO3 (BTO) showed two pronounced anomalies at approximately 112 C and 11 C, which correspond to the cubic-tetragonal and tetragonal-orthorhombic phase transition temperature, respectively. These temperatures were lower by more than 10 C compared to those of the pure BaTiO3 suggesting that the disorder introduced by oxygen vacancies lowers the phase transition temperatures. The paraelectric phase of the reduced BaTiO3 were characterized by substantial softening of the longitudinal acoustic mode and the growth of central peaks centered at zero frequency. These anomalies were observed in a certain temperature range above the Curie temperature, indicating that pretransitional precursor polar clusters exist in the cubic phase and that their dynamics are responsible for the acoustic anomalies caused by electrostrictive coupling between the strain and the polarization. The relaxation time of the precursor polar clusters derived from the central peak exhibited a critical slowing-down behavior showing that their dynamics becomes more sluggish as temperature approaches the Curie point.
Diffuse Phase Transition of Potassium Lithium Niobate Single Crystals Probed by Brillouin Scattering
고재현,Do Han Kim,Seiji Kojima,Byeong-Eog Jun,황윤홰 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
A Brillouin light scattering study has been carried out on tungsten-bronze K5.80Li3.82Nb10.12O30 (KLN-1) single crystals, which exhibited diffuse ferroelectric phase transitions at Tc 700 K. Polarized central peaks (CPs) were observed in the paraelectric phase, indicating the existence of precursor polar clusters. The relaxation time, estimated from the width of the CP, showed a substantial increase at T Tc + 100 K, at which the polar clusters seemed to become more correlated and longer lived than at higher temperatures, similar to the case of the most typical uniaxial relaxor, (Sr0.61Ba0.39)5Nb10O30 (SBN-61). The temperature dependence of the relaxation time showed a different behavior from that of the typical order-disorder-type ferroelectrics, which has been ascribed to the intrinsic disorder of the unfilled tungsten-bronze structure and the resulting quenched random electric fields. A Brillouin light scattering study has been carried out on tungsten-bronze K5.80Li3.82Nb10.12O30 (KLN-1) single crystals, which exhibited diffuse ferroelectric phase transitions at Tc 700 K. Polarized central peaks (CPs) were observed in the paraelectric phase, indicating the existence of precursor polar clusters. The relaxation time, estimated from the width of the CP, showed a substantial increase at T Tc + 100 K, at which the polar clusters seemed to become more correlated and longer lived than at higher temperatures, similar to the case of the most typical uniaxial relaxor, (Sr0.61Ba0.39)5Nb10O30 (SBN-61). The temperature dependence of the relaxation time showed a different behavior from that of the typical order-disorder-type ferroelectrics, which has been ascribed to the intrinsic disorder of the unfilled tungsten-bronze structure and the resulting quenched random electric fields.
(+)-데커시놀 (Decursinol)의 비정질화 가능성 및 단결정의 상전이에 대한 연구
고재현,김태현,정세훈,전종갑 한국물리학회 2013 새물리 Vol.63 No.4
(+)-Decursinol is a linear dihydrocoumarin isolated from the root of Angelica gigas Nakai (Umbelliferae) and is known to have cytotoxic activity, anti-Helicobacter pylori activity, and strong antinociceptive activity. The elastic properties of a (+)-decursinol single crystal were investigated by using a Brillouin light scattering technique. The acoustic phonons exhibited anomalous behaviors at about 65 $^\circ$C indicating the existence of structural phase transition at that temperature. The low-temperature elastic property of the (+)-decursinol single crystal could be explained by using two models based on normal lattice anharmonicity. The melted (+)-decursinol was quenched at liquid-nitrogen temperature to check whether it could be transformed into an amorphous state, but the quenched sample was crystallized even at the lowest temperature, indicating a high tendency for crystallization. 당귀에서 추출되는 물질 중 하나인 (+)-데커시놀은 항암, 항헬리코박터파이롤리 및 강력한 진통작용을 나타내는 약제물질이다. 본 연구에서는(+)-데커시놀 단결정의 탄성특성을 브릴루앙 분광법을 이용해조사하였다. 그 결과 측정된 음향포논의 주파수 및 반치폭이 섭씨 65도부근에서 비정상성을 보임을 확인하였고 이를 통해 (+)-데커시놀이 상온이상에서 구조상전이를 보임을 알 수 있었다. (+)-데커시놀의종음향포논이 저온 영역에서 보이는 탄성특성은 격자 비조화성에 기반한이론적 모델로 설명할 수 있었다. (+)-데커시놀이을 녹인 후에 10$^\circ$C/min의 냉각속도로 급냉하여 비정질상을 얻고자 하였으나 이물질은 액체질소 온도에서도 결정화가 일어나는 등 높은 결정화 경향성을가짐을 알 수 있었다.
고재현,이호 대한재활의학회 2004 Annals of Rehabilitation Medicine Vol.28 No.5
We presented a 64-year-old man who complained sudden onset of ulnar sided wrist pain, paresthesia in ulnar aspect of left hand after swinging a golf club. The intermittent pain was not relieved by physical therapy, local injection and medication on local clinics. Physical examination revealed tenderness on the area of the hook of hamate and weakness on flexion of 5th finger in the left side. Plane X-ray and electrodiagnostic study did not show abnormal findings. Bone scan revealed increased uptake localized on left ulnar site of wrist joint. For proper diagnosis, MRI and carpal tunnel view of left wrist were performed and fracture of the hook of hamate was found. We reported a case of non-union of golf related fracture of the hook of hamate by delayed diagnosis with the review of literatures.
고재현,T.H. Kim,S. Kojima,K. Roleder,D. Rytz,C.J. Won,허남정,정종훈,구태영,S.B. Kim,박기복 한국물리학회 2012 Current Applied Physics Vol.12 No.4
The temperature variations of the elastic constant C11 and the corresponding acoustic attenuation coefficient of barium titanate single crystals grown by two different methods in the paraelectric phase were obtained in a wide temperature by means of Brillouin light scattering. Two phenomenological approaches were adopted to attempt to explain the anomalous change in C11 (denoted as DC11) in the paraelectric phase. ΔC11 exhibited a logarithmic variation as log[(T-T0)/T0] in a certain temperature range from Tc to about Tc+ 80 ℃ instead of the other variation of (T-T0) predicted by the mean-field approach. This temperature range was almost the same as the range where precursor dynamics were theoretically predicted to set in. The fact that the logarithmic variation was proposed for uniaxial systems might indicate that the correlated deformation of precursor polar clusters is tetragonal, as was suggested from nuclear magnetic resonance study [7].
Elastic Anomalies Associated with the Antiferroelectric Phase Transitions of PbHfO3 Single Crystals
고재현,Krystian Roleder,Andrzej Majchrowski,Annette Bussmann-Holder 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.8
The temperature dependence of the elastic properties of antiferroelectric PbHfO3 was investigatedby using Brillouin scattering. The two structural phase transitions of antiferroelectricantiferroelectric-paraelectric phases were clearly identified from the discontinuous changes in theacoustic mode frequencies and the hypersonic damping. The substantial softening of the modefrequency, along with the remarkable increase in the acoustic damping observed in the paraelectricphase, indicated the formation of precursor noncentrosymmetric (polar) clusters and their couplingto the acoustic waves. This was corroborated by the observation of quasi-elastic central peaks,the intensity of which grew upon cooling toward the Curie point. The obtained relaxation timeexhibited a slowing-down behavior, suggesting that the dynamics of the precursor clusters becamemore sluggish on approaching the phase transition temperature.