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고영호,Muhtar Ahart,고재현,송종현 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.4
High-pressure Brillouin spectroscopy was applied to clarify quantitatively the physical and mechanical differences of a polymer with distinct structures consisting of the same elements. The pressure dependences of elastic properties, Young’s modulus, the shear modulus, the bulk modulus, and Poisson’s ratio for an amorphous poly (-ethylene terephthalate-) [(-PET-)] and a semi-crystalline PET were compared for pressures up to 11 GPa. A collapse of the free volume for the two PETs was ascertained at the different values of the pressure with different slopes for the elastic properties, Young’s modulus, the shear modulus, and the bulk modulus. Although the Poisson’s ratios of a semi-crystalline PET increased linearly with increasing pressure, those of an amorphous PET were almost constant. The P-V equation of state (EOS) for an amorphous PET was also determined, and isothermal bulk moduli extracted from the Birch-Murnaghan and the Vinet EOSs were 6.3 ± 0.2 GPa and 6.7 ± 0.1 GPa, respectively.
Raman Scattering Study of Relaxor Ferroelectric Pb(Sc1/2Nb1/2)O3 Crystals
Kohei Suzuki,SeijiKojima,Muhtar Ahart,Yonghong Bing,Zuo-Guang Ye 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8
The effects of B-site ordering and vacancies were studied in the relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 (PSN) family by using Raman scattering spectroscopy. Differences with Raman spectra and the depolarization ratios were clearly observed among B-site disordered PSN (PSN-D),B-site ordered with lead/oxygen vacancies PSN (PSN-OV ), and 0.7Pb(Sc1/2Nb1/2)O3-0.3PbTiO3(PSN-30PT) single crystals. The temperature dependence of the depolarization ratio of PSN-30PT was also studied to clarify the ferroelectric phase transitions and the polarization fluctuations in the polar nanoregions.
김재현,최진영,Min-Seok Jeong,고재현,Muhtar Ahart,고영호,김광주 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
A high-pressure Brillouin spectrometer with which the elastic properties of condensed matter could be measured over a wide pressure range was developed. A wide-angle, symmetric-type diamond anvil cell and an optical microscope were combined with a tandem Fabry-Perot interferometer and an optical stage to carry out both symmetric forward scattering and backscattering experiments under the same conditions. The constructed high-pressure Brillouin spectrometer was applied to ethylene-vinyl acetate (EVA) over a pressure range from ambient pressure to ∼13 GPa. The observed Brillouin spectra consisted of one Brillouin doublet caused by longitudinal acoustic waves. The Brillouin shift and the corresponding longitudinal sound velocity increased with increasing pressure. The combination of the two scattering geometries enabled us to obtain the refractive index of EVA at ambient pressure. This experimental technique will be useful in obtaining the equation of states of various types of condensed matter.
Ko, Jae-Hyeon,Jeong, Min-Seok,Lee, Byoung Wan,Kim, Jae Hyun,Ko, Young Ho,Kim, Kwang Joo,Kim, Tae Hyun,Kojima, Seiji,Ahart, Muhtar Optical Society of Korea 2013 한국광학회지 Vol.24 No.5
Brillouin spectroscopy has been widely used for the investigation of acoustic properties of condensed matters in the hypersonic region. A high-pressure Brillouin spectrometer was set up by combining a diamond anvil cell and a tandem multi-pass Fabry-Perot interferometer. It was successfully applied to liquid ethanol, and the pressure dependence of the sound velocity, the refractive index and other acoustic properties were derived based on the measurements. The detailed optical setup and experimental procedure are described.