• 한국결정성장학회지
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• 제5권4호
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• pp.394-399
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• 1995

산소 팔면체의 tilting에 의한 초격자 구조를 하고 있는 $(Na_{0.5}Sr_{0.5})(Ti_{0.5}Nb_{0.5})O_{3}$의 온도 변화에 다른 유전 특성 및 X-선 회절에 의한 구조의 변화를 살펴보았다. 유전 손실 측정에서 관측되는 380 K 부근의 peak는 primitive cell이 정방정에서 입방정으로 변화함에 따라 생기는 peak임을 알 수 있었으며 이 때 유전율의 변화는 관측되지 않았다. 따라서 유전 손실이 재료 내의 구조적 변화를 인지하는데 유전율보다 민감하다는 것을 알 수 있었다. Primitive cell 이 입방정으로 변화한 후에도 산소 팔면체의 tilting에 의한 초격자 회절선은 여전히 관측되었으며 500 K 정도에서 완전히 사라짐을 알 수 있었다. 하지만 이때 유전 특성의 변화는 관측되지 않았다.

• 한국세라믹학회지
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• 제23권5호
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• pp.25-34
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• 1986

This study was to refined the crystal structure of solid solution to determine the position and amount of Al in diopside and to relate crystal structure changes and properties of solid solution. Single crystals of the solid solution in the system CaO.MgO.$2 SiO_2-Al_2O_3$ were made from the melt with slow cooling and used to refine the structure. The following were obtained. 1. Tetrahedra rotated around axis parallel to the direction which the angle 03-03-03 became small. 2. Tetrahedron became large and regular. Average T-O bond distance increased 0.53 percent. 3. M1 octahedron became small and average M1-O bond distance decreased 1.1 percent. 4, M2 polyhedron became small and average M2-O bond distance decreased 0.37 percent Polythedron was affected not so much compared with any cation site. 5. Distance between metal ions distances between T and oxygens which were coordinated with M2 and meighboring tetrahedron distances between M2 and oxygens which coordinated with M1 and M2 were not changed almost. 6. $Al^{3+}$ substituted 4Mg^{2+}$ and $Si^{4+}$

• 한국세라믹학회지
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• 제48권6호
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• pp.493-498
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• 2011

Optimal atomic configurations in a nanoparticle were predicted by genetic algorithm. A truncated octahedron with a fixed composition of 1 : 1 was investigated as a model system. A Python code for genetic algorithm linked with a molecular dynamics method was developed. Various operators were implemented to accelerate the optimization of atomic configuration for a given composition and a given morphology of a nanoparticle. The combination of random mix as a crossover operator and total_inversion as a mutation operator showed the most stable structure within the shortest calculation time. Pt-Ag core-shell structure was predicted as the most stable structure for a nanoparticle of approximately 4 nm in diameter. The calculation results in this study led to successful prediction of the atomic configuration of nanoparticle, the size of which is comparable to that of practical nanoparticls for the application to the nanocatalyst.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.452-452
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• 2011

Using ab initio calculations, we reveal the origins of the extraordinarily increased electric conductivity of the LaAlO3/SrTiO3 interface. In both of the two (LaAlO3)m/ SrTiO3 heterojunction models (m=3, 5), the oxygen atoms in the cells were displaced toward the n-type interface and the Ti-centered octahedron structure was compressed along the [001] direction by the atomic reconstructions at the (LaAlO3)m/(SrTiO3)4 interfaces. As a result, the 3dxy orbital of the Ti atom was preferentially occupied due to the lowered energy state of the 3dxy orbital, which arises from the crystal field asymmetry. We reason that the extra electrons occupy the 3dxy orbital are accumulated at the interface by the displacement of the oxygen atoms. This accumulation contributes to the conductivity of the n-type interface. In addition, through a comparison of the atomic displacements and charge accumulation amounts between the two thickness models (m=3, 5), the thickness-dependency of the conductivity can be explained.

• 반도체디스플레이기술학회지
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• 제10권1호
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• pp.95-99
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• 2011

$(1-x)BaTiO_3+(x)Cd_5(PO_4)_3Cl$ ceramics were prepared by the conventional ceramic technique, i.e., solid state reaction at high temperature. The concentration of $Cd_5(PO_4)_3C$ was varied from 0.01 to 0.15 mole fraction. In order to study the phase transitions of our ceramics, the Raman scattering spectra were measured as functions of concentration x and temperature. It was found that the soluble limit of $Cd_5(PO_4)_3Cl$ in $BaTiO_3$ was the x=0.05 composition and $BaTiO_3$ phase disappeared above x=0.10. A new phase identified as $Ba_4Ti_3P_2O_{15}$ was detected in all samples of our compositions. The Curie temperature shifts up to $130^{\circ}C$ as the concentration x increases from zero to 0.05 and shift down to $95^{\circ}C$ as further increases to 0.08. For the increase of the Curie temperature, it is suggested that it can result from the inhibition of displacement of $Ti^{4+}$ in the distorted octahedron due to well dispersed $Ba_4Ti_3P_2O_{15}$ and $Cd_5(PO_4)_3Cl$ phase.

• 한국결정학회지
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• 제13권1호
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• pp.17-20
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• 2002

[Zn(L)₂(H₂O)₄] (1) (L = isonicotinate) 착물을 합성하고 구조를 규명하였다 이 착물은 삼사정계, 공간군 P1, a = 6.9062(4) , b = 9.2618(7) , c = 6.3313(3) , α = 104.986(6)°, β = 112.865(4)°, γ = 96.213(6)°, V : 350.41(4) ³, Z = 1로 결정화 되었다. 이 착물의 구조는 최소자승법으로 정밀화하였으며, 최종신뢰도 R₁(wR₂)값은 1225개의 회절반점에 대하여 0.0209및 0.0591이었다. Zn 원자의 배위환경은 isonicotinate 리간드가 서로 trans에 위치한 팔면체 구조를 갖는다 . 또한 화합物 1은 수소결합에 의한 이차원의 사슬 구조로 연결되어 있다

• 한국자기학회지
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• 제22권4호
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• pp.121-124
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• 2012

Cubane-type $Mn_4$ 클러스터의 전기구조 및 자기적 성질을 제1원리의 범밀도함수법을 이용하여 계산하였다. 그 결과, 전자구조는 벌크 MnO와 비슷한 Mn 주위의 팔면체 산소 원자에 의해 $t_{2g}$, $e_g$ 에너지 준위로 분리되어 있었다. 총에너지계산에서는 초교환작용으로 인해 반강자성적 상호작용이 가장 낮은 에너지를 가지고 있었고, Mn 원자 사이의 교환 상호작용 크기를 얻었다. Mn 사이의 교환 상호작용은 스핀이 평행인 원자사이보다 반평행인 원자사이에서 더 큰 값을 가지고 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.391-394
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• 2006

Growth characteristics of methane-propane clathrate hydrate, growing under different undercooling conditions, was investigated. After the water within pressurized vessel was fully saturated with guest gas molecules by agitation, medium was rapidly undercooled and maintained at the constant temperature. The growth of hydrate was always Initiated with film formations at the upper bounding surface of liquid pool. The visual observation using microscope revealed detailed features of subsequent crystal nucleation, migration, growth and interference occurring within liquid pool. A number of small crystals ascended and settled at the hydrate film. When undercooling was small $({\Delta}T=3.2K)$, some of the settled crystals slowly grew into faceted columns. As the undercooling increased, the downward growth of crystals underneath the hydrate film became dendritic and occurred with greater rate and with finer arm spacing. The shapes of the floating crystals were diverse and included octahedron and triangular or hexagonal platelet When the undercooling was small, the octahedral crystals were found dominant. As the undercooling increased, the shape of the floating crystals also became dendritic. The detailed characteristics of floating crystals were reported in this study.

• Bulletin of the Korean Chemical Society
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• 제18권6호
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• pp.653-656
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• 1997

The new unsymmetric $N_6$ ligand 1-amino-13-(2-pyridyl)-3,6,9,12-tetraazatridecane (aptatd) containing one pyridyl group has been synthesized and characterized by EA, IR, and NMR. Its proton association constants $(log K_H^n)$ and stability constants $(log K_{ML})$ for Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ), and Zn(Ⅱ) ions were determined at 298.1 K and ionic strength 0.100 mol $dm^{-3}$ (KNO₃) in aqueous solution by potentiometry: log $K_H^1$=8.80, log $K_H^2$=8.49, log $K_H^3$=6.84, log $K_H^4$=4.17, log $K_H^5$=3.47; log $K_{ML}(Co^{2+})$=18.00, log $K_{ML}(Ni^{2+})$=21.31, log $K_{ML}(Cu^{2+})$=23.62, log $K_{ML}(Zn^{2+})$=15.60. The X-ray structure of its nickel(Ⅱ) complex [Ni(aptatd)]$(ClO_4)_2$ are reported: orthorhombic space group Pbca, a=15.715(1) Å, b=14.280(2) Å, c=19.443(2) Å, V=4363.4 (9) ų with Z=8. The geometry around nickel is a distorted octahedron with the pyridine nitrogen atom being cis to the nitrogen atom of the terminal primary amine.

• 한국자기학회지
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• 제9권3호
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• pp.131-135
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• 1999

층상 페로브스카이트형 구조를 가진 망간 산화물의 전자구조를 이해하기 위하여 단일 층상을 가진 LaSrMnO4의 전자구조를 제1원리의 국소 밀도 범함수 이론을 근거로 사용하는 Full Potential Linearized Augmented Plane Wave(FLAPW)방법으로 구하였다. 또한 홀 농도 변환에 따른 자기구조의 변화의 이해를 위해 Mn4+의 Sr2MnO4의 전자구조 계산을 행하여 전자구조를 비교하였다. 총에너지 계산 결과, LaSrMnO4는 면내의 반강자성 구조가 강자성 구조보다 더 낮은 에너지를 가지고 있었다. 또한, Mn-O 팔면체의 c축으로의 야안-텔러 왜곡(Jahn-Teller distortion)에 의해 에너지 갭이 나타나며, 이에 따른 3z2-r2 궤도 정렬에 의해 2차원 면내의 반강자성 상태가 안정됨을 볼 수 있었다.