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Ky-Nam Pham,이한복,한형수,강진규,이재신,Aman Ullah,안창원,김일원 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.2
The effects of niobium substitution on the crystal structure and on the ferroelectric and piezoelectric properties of Bi1/2(Na0.82K0.18)1/2(Ti)O3 (BNKT) ceramics have been investigated. X-ray diffraction analyses revealed that Nb-substitution induced a phase transition from the coexistence of rhombohedral-tetragonal symmetry to pseudocubic symmetry. Accordingly, the electric-fieldinduced polarization and strain hysteresis loops indicated that Nb substitution significantly disrupted the ferroelectric order of BNKT ceramics, leading to degradations in the remnant polarization,coercive field, and piezoelectric coefficient d33. However, the destabilization of the ferroelectric order was accompanied by a significant enhancement in the electric-field-induced strain (EFIS),which peaked at x = 0.03 with a value of 0.47%. The abnormal enhancement in the EFIS could be attributed to a phase transition from a non-polar to a polar phase under an applied electric field.
Bi1/2(Na0.8K0.2)1/2TiO3 세라믹스의 유전 및 압전 특성에 대한 Bi(Mg1/2Sn1/2)O3 변성 효과
Ky Nam Pham,딘티힌,이현영,공영민,이재신 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.3
The effect of Bi(Mg1/2Sn1/2)O3 (BMS) modification on the crystal structure, ferroelectric and piezoelectric properties of Bi1/2(Na0.8K0.2)1/2TiO3 (BNKT) ceramics has been investigated. The BMS-substitution induced a transition from a ferroelectric (FE) tetragonal to a nonpolar pseudocubic phase, leading to degradations in the remnant polarization, coercive field, and piezoelectric coefficient d33. However, the electric-fieldinduced strain was significantly enhanced by the BMS substitution-induced phase transition and reached a highest value of Smax/Emax=633 pm/V under an applied electric field of 6 kV/mm when the BMS content reached 6 mol%. The abnormal enhancement in strain was attributed to the field-induced transition of the pseudocubic symmetry to other asymmetrical structure, which was not clarified in this work.
Strain Enhancement of Lead-free Bi1/2(Na0.82K0.18)1/2TiO3 Ceramics by Sn Doping
이재신,Ky-Nam Pham,한형수,이한복,Vu Diem Ngoc Tran 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.2
The effects of Sn doping on the crystal structure, electric-field-induced strain (EFIS), and piezoelectric properties of Bi1/2(Na0.82K0.18)1/2TiO3 ceramics have been investigated. Sn doping resulted in a transition from ferroelectric (FE) tetragonal to electrostrictive (ES) pseudocubic symmetry,leading to degradations of the piezoelectric coupling coefficient, electromechanical quality factor,and piezoelectric coefficient d33. However, the EFIS was significantly enhanced by the Sn-dopinginduced phase transition and reached its highest value of Smax/Emax = 585 pm/V when 5 mol%SnO2 was doped, which is close to the FE-ES phase boundary. To explain the giant strain, we suggest a model on the basis of a field-induced phase transition from nonpolar to polar symmetry under external fields.
팜키남,딘치힌,이현영,공영민,이재신,Pham, Ky Nam,Dinh, Thi Hinh,Lee, Hyun-Young,Kong, Young-Min,Lee, Jae-Shin 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.3
The effect of $Bi(Mg_{1/2}Sn_{1/2})O_3$ (BMS) modification on the crystal structure, ferroelectric and piezoelectric properties of $Bi_{1/2}(Na_{0.8}K_{0.2})_{1/2}TiO_3$ (BNKT) ceramics has been investigated. The BMS-substitution induced a transition from a ferroelectric (FE) tetragonal to a nonpolar pseudocubic phase, leading to degradations in the remnant polarization, coercive field, and piezoelectric coefficient $d_{33}$. However, the electric-field-induced strain was significantly enhanced by the BMS substitution-induced phase transition and reached a highest value of $S_{max}/E_{max}$ = 633 pm/V under an applied electric field of 6 kV/mm when the BMS content reached 6 mol%. The abnormal enhancement in strain was attributed to the field-induced transition of the pseudocubic symmetry to other asymmetrical structure, which was not clarified in this work.
Kim, Dae-Uk,Lee, Han-Bok,Hung, Nguyen Viet,Pham, Ky Nam,Han, Hyoung-Su,Lee, Jae-Shin The Korean Powder Metallurgy Institute 2010 한국분말재료학회지 (KPMI) Vol.17 No.5
The effects of high energy ball-milling (HEBM) on the sintering behavior and piezoelectric properties of 0.1 wt% $Li_2CO_3$ doped 0.8Pb($Mg_{1/3}Nb_{2/3}$)$O_3$-0.2Pb($Zr_{0.475}Ti_{0.525}$)$O_3$ (PMN-PZT) ceramics were investigated. It was found that HEBM treatment was quite effective to reduce the average particle size down to 300 nm, leading to increased density as well as enhanced piezoelectric properties of a sintered specimen even though prolonged HEBM resulted in unwanted secondary phases that caused a degradation of piezoelectric properties. The dielectric constant ($\varepsilon_r$), piezoelectric coupling factor ($k_p$) and piezoelectric constant $d_{33}$ of 0.1 wt% $Li_2CO_3$ doped PMN-PZT ceramics prepared via HEBM for 10 h reached 2040, 0.68 and 554 pC/N, respectively.
Antioxidant Activities of Vietnamese Medicinal Plants
Phuong Thien Thuong,나민균,Nguyen Hai Dang,Tran Manh Hung,Pham Thanh Ky,Tran Van Thanh,Nguyen Hai Nam,Nguyen Duy Thuan,석대은,배기환 한국생약학회 2006 Natural Product Sciences Vol.12 No.1
hundred and twenty six Vietnamese traditional herbals belonging to 59 families were screened forof seven plants, including Euphorbia thymifolia (leaf), Gnetum montanum (stem), Heterosmilax erythrantha(root), Morus alba (leaf), Syzygium formosum (leaf), Jussiaea repens (aerial parts), and Camellia sinensis (leaf),exhibited significant antioxidant activities. All of these herbs showed remarkable free radical scavenging activitieswith IC50 values of 11.0, 14.5, 17.0, 13.6, 10.8, 7.7, and 8.5g/ml, respectively, and significant inhibitory effectsconcentration of 50g/ml.KeywordsVietnamese medicinal plants, antioxidant activity, free radical scavenging, lipid peroxidation
Giant Strain in Lead-free Relaxor/Ferroelectric Piezocomposite Ceramics
Thi Hinh Dinh,Jin-Kyu Kang,Hoang Thien Khoi Nguyen,Trang An Duong,Jae-Shin Lee,Vu Diem Ngoc Tran,Ky Nam Pham 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12
The crystal structural, ferroelectric, and electric-field-induced-strain (EFIS) properties of leadfree relaxor/ferroelectric piezocomposites were investigated. The relaxor-matrix phases were mixed with the ferroelectric-seed phases by using a conventional ceramic processing route. The addition of the ferroelectric seed phase dramatically enhanced the EFIS of the relaxor matrix phase at low electric fields. Giant strains of 745 pm/V at 4 kV/mm and 466 pm/V at 3 kV/mm were obtained when the seed contents were 30 wt% and 50 wt%, respectively, which are much higher than those of the relaxor matrix phase without ferroelectric seeds (575 pm/V at 4 kV/mm and 327 pm/V at 3 kV/mm).