• 한국재료학회지
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• 제21권7호
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• pp.391-395
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• 2011

The structure and dielectric properties of poled <001>-oriented 0.7Pb($Mg_{1/3}Nb_{2/3})O_3-0.3PbTiO_3$ (PMN-0.3PT) crystals have been investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric field induced monoclinic phase was observed for the initial poled sample. The phase remained stable after the field was removed. A quite different temperature dependence of dielectric constant has been observed between heating and cooling due to an irreversible phase transformation. The results of mesh scans and temperature dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase at 370K and to a paraelectric cubic phase at 405K upon heating. However, upon subsequent cooling from the unpoled state, the cubic phase changes to a poly domain tetragonal phase and to a rhombohedral phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that of the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary and at the phase transition temperature.

• 한국재료학회지
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• 제18권1호
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• pp.1-4
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• 2008

The phase transformations and luminescent properties of Eu-doped $Ca_{1-x}Sr_xAl_2O_4$ phosphors were investigated. $Ca_{1-x}Sr_xAl_2O_4:Eu^{2+}$ phosphors were synthesized by a solid-state reaction with a flux, $H_3BO_3$. A phase transformation from monoclinic $CaAl_2O_4$ to monoclinic $SrAl_2O_4$ was observed as the x values increased. A high-temperature hexagonal phase of $SrAl_2O_4$ was formed during this transformation as an intermediate phase under an $H_2$ atmosphere due to oxygen vacancies; this did not occur in an air atmosphere. Accordingly, the emission spectra shifted from a blue region to a green region as x increased.

• 폴리머
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• 제33권2호
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• pp.183-188
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• 2009

일축인장에 의하여 변형핀 1-옥텐 공단량체를 함유하는 폴리에틸렌과 고밀도 폴리에틸렌을 대상으로 이들의 온도 상승에 따른 구조 이완 거동을 방사광 가속기를 이용한 실시간 광각 및 소각 X-선 산란법으로 연구하였다. 일축 변형된 폴리에틸렌은 온도가 상승함에 따라 결정의 전이, 부서진 라멜라의 재배열 등 구조적 변화거동이 수반 되었으며 이는 공단량체의 합량에 따라 매우 다르게 나타났다. 공단량체 함량이 2 wt% 이하인 폴리에틸렌의 경우 일축 변형 과정에서 마르텐사이트 전이에 의해 생성된 monoclinic 격자가 온도 상승에 따라 orthorhombic 결정격자로 재전이되고 부서진 라멜라간 재배열 거동을 보였으나 9.5 wt%의 고함량에서는 라멜라의 재배열 거동이 관찰되지 않았으며 결정 격자의 전이 거동도 관찰되지 않았다.

• 한국재료학회지
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• 제29권9호
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• pp.519-524
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• 2019

Spherical $Li_3V_2(PO_4)_3$ (LVP) and carbon-coated LVP with a monoclinic phase for the cathode materials are synthesized by a hydrothermal method using $N_2H_4$ as the reducing agent and saccharose as the carbon source. The results show that single phase monoclinic LVP without impurity phases such as $LiV(P_2O_7)$, $Li(VO)(PO_4)$ and $Li_3(PO_4)$ can be obtained after calcination at $800^{\circ}C$ for 4 h. SEM and TEM images show that the particle sizes are $0.5{\sim}2{\mu}m$ and the thickness of the amorphous carbon layer is approximately 3~4 nm. CV curves for the test cell are recorded in the potential ranges of 3.0~4.3 V and 3.0~4.8 V at a scan rate of $0.01mV\;s^{-1}$ and at room temperature. At potentials between 3.0 and 4.8 V, the third $Li^+$ ions from the carbon-coated LVP can be completely extracted, at voltages close to 4.51 V. The carbon-coated LVP exhibits an initial specific discharge capacity of $118mAh\;g^{-1}$ in the voltage region of 3.0 to 4.3 V at a current rate of 0.2 C. The results indicate that the reducing agent and carbon source can affect the crystal structure and electrochemical properties of the cathode materials.

• 한국표면공학회지
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• 제55권6호
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• pp.368-375
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• 2022

YSZ (Yttria Stabilized Zirconia) is used as a thermal barrier coating material for gas turbines due to its low thermal conductivity and high fracture toughness. However, the operating temperature of the gas turbine is rising according to the market demand, and the problem that the coating layer of YSZ is peeled off due to the volume change due to the phase transformation at a high temperature of 1400℃ or higher is emerging. To solve this problem, various studies have been carried out to have phase stability, low thermal conductivity, and high fracture toughness in a high temperature environment of 1400℃ or higher by doping trivalent and tetravalent oxides to YSZ. In this study, the monoclinic phase formation behavior and crystallinity were comparatively analyzed according to the total doping amount of oxides by controlling the doping amounts of Sc₂O₃ and Gd₂O₃, which are trivalent oxides, and TiO₂, which are tetravalent oxides, in YSZ. Through comparative analysis of monoclinic phase formation and crystallinity, the thermal conductivity of the thermal barrier coating layer according to the amount of doping was predicted.

• 한국분말재료학회지
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• 제29권6호
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• 분석과학
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• 제19권4호
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• pp.309-315
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• 2006

Two piperazine-templated metal sulfate complexes, $(C_4N_2H_{12})[Ni(H_2O)_6](SO_4)_2$, I and ($C_4N_2H_{12}$) $[Co(H_2O)_6](SO_4)_2$, II, have been synthesized by hydro/solvothermal reactions and their crystal structures analyzed by single crystal X-ray diffraction methods. Complex I crystallizes in the monoclinic system, $P2_1/n$ space group, a=12.920(3), b=10.616(2), $c=13.303(2){\AA}$, ${\beta}=114.09(1)^{\circ}$, Z=4, $R_1=0.030$ for 3683 reflections; II: monoclinic $P2_1/n$, a=12.906(3), b=10.711(2), $c=13.303(2){\AA}$, ${\beta}=114.10(2)^{\circ}$, Z=4, $R_1=0.032$ for 4010 reflections. The crystal structures of the piperazine-templated metal(II) sulfates demonstrate zero-dimensional compound constituted by diprotonated piperazine cations, metal(II) cations and sulfate anions. The structures of complex I and II are substantially isostructural to that of the previously reported our piperazine-templated copper(II) sulfate complex $(C_4N_2H_{12})[Cu(H_2O)_6](SO_4)_2$. The central metal(II) atoms are coordinated by six water molecules in the octahedral geometry. The crystal structures are stabilized by three-dimensional networks of the $O_{water}-H{\cdots}O_{sulfate}$ and $N_{pip}-H{\cdots}O_{sulfate}$ hydrogen bonds between the water molecules and sulfate anions and protonated piperazine cations. Based on the results of thermal analysis, the thermal decomposition reactions of the complex I was analyzed to have three distinctive stages whereas the complex II proceed through several stages.

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.620-626
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• 2015

$Ho^{3+}$가 도핑된 $SrAl_2O_4$ 상향전환 형광체 분말을 분무열분해법으로 제조하고 활성제의 농도, 후 열처리 온도 변화에 따른 결정학적 구조와 발광 특성을 조사하였다. 또한 유기 첨가제 사용에 따른 형광체의 결정구조, 표면적 및 휘도 변화를 조사하였다. $SrAl_2O_4:Ho^{3+}$는 $Ho^{3+}$의 $^5F_4/^5S_2{\rightarrow}^5I_8$ 전이에 기인한 강한 녹색 발광을 보였다. 가장 높은 발광 강도를 보이는 $Ho^{3+}$ 농도는 0.1%였고, 그 이상의 농도에서는 활성 이온간 쌍극자-쌍극자 상호 작용에 의에 농도소강이 일어나 발광 휘도는 급격히 감소하였다. 여기 광원의 전력 세기에 따른 발광 휘도 변화 관찰로부터 $SrAl_2O_4:Ho^{3+}$의 녹색 발광은 2광자가 관여된 바닥상태흡수-여기상태흡수 과정을 통해 효율적으로 일어남이 확인되었다. 합성된 분말의 주상은 단사정계이고 일부 육방정계 상이 존재하였다. 후 열처리 온도를 $1000^{\circ}C$에서 $1350^{\circ}C$로 증가시킴에 따라 $SrAl_2O_4:Ho^{3+}$는 육방정계 상이 줄어 들면서 단상정계의 결정성이 향상되었다. 그러나 $1350^{\circ}C$에서도 일부 육방정계 상은 존재하였다. 구연산(CA)과 에틸렌 글리콜(EG)을 첨가해준 분무 용액으로부터 제조한 경우, 육방정계 상이 없는 순수한 단사정계 상으로 향상된 결정성을 가지는 $SrAl_2O_4:Ho^{3+}$가 제조되었다. 또한 유기 첨가제와 함께 N,N-Dimethylformamide(DMF)를 분무용액에 넣어 줌으로써 형광체의 표면적을 크게 감소시킬 수 있었다. 그 결과 CA/EG/DMF를 넣고 제조한 $SrAl_2O_4:Ho^{3+}$ 형광체는 유기 첨가물 없이 제조한 형광체에 비해 발광 휘도가 약 168% 향상되었다. 이러한 휘도 증대는 $SrAl_2O_4:Ho^{3+}$ 형광체의 결정상이 순수해졌고, 결정성 증대와 표면 결함을 최소화시킨 결과라고 결론지었다.

• 대한화학회지
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• 제39권9호
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• pp.715-721
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• 1995

Trans-$[Co(py)_4/Ci_2]^+(py=pyridine)$과 L-proline 및 diimine(=2,2'-bipyridine,1,10-phenanthroline)과의 반응에서 $[Co(L-pro)_2/(bipy)]^+$(L-pro=bipy=2,2'-bipyridine)과 $[Co(L-pro)_2(phen)]^+$(phen=1,10-phenathroline)이 각각 생성되었다. 관 크로마토그래피상에서 입체특이성을 가지는 L-prolinato의 입체선택성으로 인하여 $[Co(L-pro)_2(bipy)]^+$에서는 $Lambda$-trans(N)만이 얻어졌고 $[Co(L-pro)_2(bipy)]^+$에서는 ${\Delta}$-trans(N)과 $Lambda$-cis(O)cis(N)이 얻어졌다. 결정구조 연구의 결과는 다음과 같다: $Lambda$-trans(N)-$[Co(L-pro)_2(bipy)]CIO_4{\cdot}2H_2O$ (1): monoclinic, space group $P2_1(#4)$, a = 9.807(3), b = 10.421(1), c = 12.778(2)${\AA}$, ${\beta}=109.90(2)^{\circ}$, V = 1227.8(5)${\AA}^3$, Z = 2; 1571 data(I>3.0${\sigma}$(I)) R = 0.060 and $R_W = 0.067$; ${\Delta}$-trans(N)-$[Co(L-pro)_2(phen)]Cl{\cdot}_3H_2O$ (2): monoclinic, space group $P2_1(#4)$, a = 9.838(2), b = 12.892(2), c = 10.747(2)${\AA}$, ${\beta}=113.79(2)^{\circ}$, V = 1247.2(4)${\AA}^3$, Z = 2; 2433 data(I>3.0${\sigma}$(I)) R = 0.043 and $R_W = 0.050$.

• Archives of Pharmacal Research
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• 제9권4호
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• pp.223-227
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• 1986

The structure of alclofenac was determined by single crystal X-ray diffraction analysis. The compound was recrystallized from chloroform solution in monoclinic system space group $C_{2}$/c, with Z = 8, a = 8, a = 23.349(9), b =14.295 (3), c = 7.192 (2) $\AA$, $\beta$ = 111.32 (3)$^{\circ}$, and $d_{dbs}$ = 1.29, $d_{caic}$ = 1.30. The structure was solved by direct method and refined by least-squares procedure to the final R-value being 0.044 for 1055 reflections (F ${\geq}6${\sigma}$(F)). The molecules are dimerized by OH..O type hydrogen bonds related by two-fold axis.