The structural distortion by a Substituent : Monosubstituted Benzene Derivative cases

Mhin, Byung-Jin 배재대학교 자연과학연구소 2004 自然科學論文集 Vol.15 No.1

The substituent dependence of geometric distortion through the two independent electronic substituent effects is analyzed for mono-substituted benzene derivatives of C_(2v). Based on resonance structures, quantitative relationships expressing the resonance and field/inductive contribution terms in bond distortions are derived. The calculated field-effect parts of C_(ipso)_C_(ortho) ring bonds increase and decrease compared to benzene for electropositive and electronegative substituents respectively. The nonbonded axial distance, C_(ipso) ‥‥C_(para') decreases for electronegative substituents and increases for electropositive substituents. As the electronegativity increases, the distance C_(ortho)‥‥C_(ortho') increases. With the π-donors, C_(meta)‥‥C_(meta') nonbonded distances are shorter compared to the ones of benzene, and for π-acceptors, they are longer. Our model based on valence bond approach predicts that the average bond length determines the area of ring, and the sum of the angle ∠C_(ortho)_C_(ipso)_C_(ortho) and ∠C_(meta)_C_(para)_C_(meta) determines the axial distance.

Pulsed-Laser-Induced Simple Synthetic Route for Tb ₃ Al ₅ O ₁₂ :Ce ³⁺ Colloidal Nanocrystals and Their Luminescent Properties

Mhin, SungWook,Ryu, JeongHo,Kim, KangMin,Park, GyeongSeon,Ryu, HanWool,Shim, KwangBo,Sasaki, Takeshi,Koshizaki, Naoto Springer 2009 NANOSCALE RESEARCH LETTERS Vol.4 No.8

<P>Cerium-doped Tb<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB>(TAG:Ce<SUP>3+</SUP>) colloidal nanocrystals were synthesized by pulsed laser ablation (PLA) in de-ionized water and lauryl dimethylaminoacetic acid betain (LDA) aqueous solution for luminescent bio-labeling application. The influence of LDA molecules on the crystallinity, crystal morphology, crystallite size, and luminescent properties of the prepared TAG:Ce<SUP>3+</SUP>colloidal nanocrystals was investigated in detail. When the LDA solution was used, smaller average crystallite size, narrower size distribution, and enhanced luminescence were observed. These characteristics were explained by the effective role of occupying the oxygen defects on the surface of TAG:Ce<SUP>3+</SUP>colloidal nanocrystal because the amphoteric LDA molecules were attached by positively charged TAG:Ce<SUP>3+</SUP>colloidal nanocrystals. The blue-shifted phenomena found in luminescent spectra of the TAG:Ce<SUP>3+</SUP>colloidal nanocrystals could not be explained by previous crystal field theory. We discuss the 5d energy level of Ce<SUP>3+</SUP>with decreased crystal size with a phenomenological model that explains the relationship between bond distance with 5d energy level of Ce<SUP>3+</SUP>based on the concept of crystal field theory modified by covalency contribution.</P>

Simple synthetic route for hydroxyapatite colloidal nanoparticles via a Nd:YAG laser ablation in liquid medium

Mhin, Sung Wook,Ryu, Jeong Ho,Kim, Kang Min,Park, Gyeong Seon,Ryu, Han Wool,Shim, Kwang Bo,Sasaki, Takeshi,Koshizaki, Naoto Springer-Verlag 2009 APPLIED PHYSICS A MATERIALS SCIENCE AND PROCESSING Vol.96 No.2

Phase evolution of (Ni, Co, Mn)O₄ during heat treatment with high temperature in situ X-ray diffraction

Mhin, S.,Han, H.,Kim, D.,Yeo, S.,Lee, J.I.,Ryu, J.H. Ceramurgica ; Elsevier Science Ltd 2016 CERAMICS INTERNATIONAL Vol.42 No.4

Phase evolution of (Ni, Co, Mn)O<SUB>4</SUB> (NMC) for negative thermal coefficient (NTC) thermistor is investigated using high temperature X-ray diffraction. Diffraction patterns were collected during heating and cooling, allowing the observation of chemical reactions in the range of temperature between 25 and 1400<SUP>o</SUP>C. NiO, Mn<SUB>3</SUB>O<SUB>4</SUB> and CO<SUB>3</SUB>O<SUB>4</SUB> as the reactant materials were prepared using spray drying. As increasing temperature, phase transformation of Mn<SUB>3</SUB>O<SUB>4</SUB> to Mn<SUB>2</SUB>O<SUB>3</SUB> was first observed prior to the formation of NMC spinel structure at 700<SUP>o</SUP>C. Between 1000 and 1200<SUP>o</SUP>C, only spinel NMC was observed without any other phases. Also, grain growth of NMC was observed. Phase transition from cubic to tetragonal was observed during cooling. With further increasing temperature up to 1400<SUP>o</SUP>C, thermal stability of NMC decrease, which was confirmed by NiO separation due to the thermal decomposition. Thermogravimetric and differential thermal analysis are performed on NMC compound and the results support the mechanism of phase formation presented by high temperature XRD data. Also, electrical resistance of NMC is measured as a function of temperature (-40-80<SUP>o</SUP>C) and the factor of thermal sensitivity (B value) is calculated.

Theoretical Study of 1,4,6,9-Tetra chlorinated dibenzo-$\rho$-dioxin anion

Mhin, Byung-Jin,Odde, Srinivas,Han, Kang-Hyun,Lee, Jung-Eun,Choi, Won-Yong 배재대학교 자연과학연구소 2005 自然科學論文集 Vol.16 No.1

The equilibrium geometry, adiabatic electron affinity, harmonic vibrational frequencies, and infrared intensities of 1,4,6,9-Tetra chlorinated dibenzo-$\rho$-dioxin anion have been studied using B3LYP method. The local minimum conformation is found to be twisted form with $D_2$ symmetry. The predicted adiabatic electron affinity is 0.54 eV. The predicted inversion barrier between twisted and planar conformers was 0.9 kcal/mol, thus we expect that experimentally observed structure seems to be planar. the characteristic IR band of 1,4,6,9-TCDD anion appears at 1510 $cm^4$, which is a benzene ring skeleton vibration mode related with CaCb and C2C3 bond. this characteristic band could be sued for identication of 1,4,6,9-TCDD anion.

Processing, structure, and properties of lead-free piezoelectric NBT-BT

Mhin, Sungwook,Lee, Jung-Il,Ryu, Jeong Ho The Korea Association of Crystal Growth 2015 한국결정성장학회지 Vol.25 No.4

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, $Pb(Zr_xTi_{1-x}O_3)$, which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, $Na_{0.5}Bi_{0.5}TiO_3$ (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, $(Na_{0.5}Bi_{0.5})_{0.93}Ba_{0.7}TiO_3$ (abbreviated as NBT-7BT), at the region of MPB using 7 % $BaTiO_3$ as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

Electrochemically activated cobalt nickel sulfide for an efficient oxygen evolution reaction: partial amorphization and phase control

Sungwook Mhin,Hyuksu Han 한국자기학회 2019 한국자기학회 학술연구발표회 논문개요집 Vol.29 No.1

High-Density Crystalline/Amorphous Phase Boundaries in Electrochemically Activated Nickel-Doped Cobalt Sulfide for Efficient Oxygen Evolution Reaction

Sungwook Mhin 한국자기학회 2018 한국자기학회 학술연구발표회 논문개요집 Vol.2018 No.3

사물 인터넷 기반 스마트 센서를 활용한 실시간 모니터링 시스템

민성욱(Sungwook Mhin),이재웅(Jaewoong Lee),김동응(Dongeung Kim),김문조(Moon-jo Kim),한혁수(Hyuksu Han),이빈(Bin Lee) 한국소성가공학회 2019 한국소성가공학회 학술대회 논문집 Vol.2019 No.5

The Structural distortion by a Substituent : Monosubstituted Benzene Derivative cases

민병진,Mhin, Byung-Jin 배재대학교 자연과학연구소 2005 自然科學論文集 Vol.15 No.1

The substituent dependence of geometric distortion through the two independent electronic substituent effects is analyzed for mono-substituted benzene derivatives of $C_{2v}$. Based on resonance structures, quantitative relationships expressing the resonance and field/inductive contribution terms in bond distortions are derived. The calculated field-effect parts of $C_{ipso}$_$C_{ortho}$ ring bonds increase and decrease compared to benzene for electropositive and electronegative substituents respectively. The nonbonded axial distance, $C_{ipso}$....$C_{para'}$ decreases for electronegative substituents and increases for electropositive substituents. As the electronegativity increases, the distance $C_{ortho}$....$C_{ortho'}$ increases. With the $\pi$-donors, $C_{meta}$....$C_{meta'}$ nonbonded distances are shorter compared to the ones of benzene, and for $\pi$-acceptors, the are longer. Our model based on valence bond approach predicts that the average bond length determined the area of ring, and the sum of the angles <$C_{ortho}$_$C_{ispo}$_$C_{ortho}$ and <$C_{meta}$_$C_{para}$_$C_{meta}$ determines the axial distance.