• The Korean Journal of Ceramics
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• 제6권4호
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• pp.339-342
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• 2000

In the present study, we attempted to apply DV-X$\alpha$ method to expressing the reactivity of materials. The expression of reactivity was discussed by comparison between ${\gamma}$-C$_2$G having hydraulic activity and ${\gamma}$-C$_2$S not having hydraulic activity at normal conditions. It was found that the model cluster used for calculation can finely reproduce the bulk and surface states using with and without point charge, respectively. The hydration state was also represented by placing OH￣ on the surface of the cluster. It was calculated that the bond strength of the first layer (as surface) was bigger than that of inner layers (as bulk) for ${\gamma}$-C$_2$S while that of the first layer for ${\gamma}$-C$_2$G was smaller than that of inner layers. Subsequently a model in which OH￣ is coordinated on Ca at the surface was also calculated. The bond strength with OH￣ was stronger than that without OH￣, while for ${\gamma}$-C$_2$G the bond strength with OH￣ was weaker than that without OH￣. From these results, it is concluded that the hydraulic activity depends on whether the bond strength for hydrated state becomes weaker than that unhydrated state or not.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.900-903
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• 2003

Using $DV-X{\alpha}$ method, it is calculated that nickel reduces the energy band gap of manganese oxide in 3 additives of titanium, nickel and tin. Therefore, it is estimated that the electrical conductivity of manganese-nickel oxide has the lowest value in 3 kinds of manganese oxide. The manganese oxide and manganese-nickel oxide which were produced by anodic deposition under $30mA/cm^2$ at room temperature in manganese sulfate and manganese-nickel sulfate solution were thermal-analyzed by DTA and TGA. The weight change of manganese oxide continuously decreased below $508^{\circ}C$ and kept constant at $518{\sim}600^{\circ}C$. However, the manganeses-nickel oxide transformed at the temperature range of $510{\sim}537^{\circ}C$. It is observed that the nickel addition to manganese oxide increases transformation temperature and its range.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.259-262
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• 2003

The surface electronic state of rutile $TiO_2$, which is an oxide semiconductor and has a wide band gap of 3.1 $\sim$ 3.5 eV, was calculated by DV-$X_{\alpha}$ method, which is a sort of the first principle molecular orbital method and uses Hartre-Fock-Slater approximation. The $[Ti_{15}O_{56}]^{-52}$ cluster model was used for the calculation of bulk state and the $[OTi_{11}O_{34}]^{-24}$ model for the surface state calculation. After calculations, the energy level diagrams and the deformation electron density distribution map were compared in both models. As results, it was identified that the surface energy levels are found between the valence and conduction band of bulk $TiO_2$ on the surface area. The energy values of these surface-induced levels are lower than conduction band of bulk $TiO_2$ by 0.1 $\sim$ 1 eV. From this fact, it is expected that the surface energy levels act as donar levels in n-type semiconductor.

• 한국재료학회지
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• 제25권11호
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• pp.642-646
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• 2015

Super alloys, which can be divided into three categories, i.e. Ni-base, Co-base, and Fe-base alloys, are widely used for high temperature applications. Since superalloys contain many alloying elements and precipitates, their chemistry and processing parameters need to be carefully designed. In this study, we designed a new Ni alloy to prevent corrosion due to water vapor and gases at high temperatures. The new alloy was designed using the theoretical value of the resulting energy electronic state calculation($DV-X{\alpha}$ method). The components that were finally used were Cr, Mo, and Ti, with Ni as a base. For these alloys, elements were selected in order to compare their values with that of the average theoretical basis for an Inconel 625 alloy. Finally, two kinds of Ni alloy were designed: Ni-28Cr-4Mo-2Ti and Ni-20Cr-10Mo-1Ti.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1535-1537
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• 2003

Manganese oxide electrode was designed to improve electrical conductivity for dimensionally stable anode(DSA) using discreet variation (DV)-X${\alpha}$ method. It was calculated in DV-X${\alpha}$ method that the addition of nickel to manganese oxide reduce the energy band gap of manganese oxide electrode. Therefore, it is estimated that nickel in 3 additive elements of Ti, Ni and Sn is the best candidate to improve the electrical conductivity of manganese oxide. The anodically deposited manganese oxide which was produced in 0.2M $MnSO_4$ and 0.2M (Mn,Ni)$SO_4$ solution had $MnSO_4$ structure which was identified by XRD. The $MnSO_4$ films produced in both solutions over than 50mA/$cm^2$ of current density and long deposition time of 600sec showed low adhesion with Ti substrate.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.691-696
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• 2004

The electronic state and chemical bonding of $\beta$-MnO$_2$ with transition metal dopants were theoretically investigated by DV-X$_{\alpha}$ (the discrete variational X$_{\alpha}$) method, which is a sort of the first principles molecular orbital method using the Hartree-Fock-Slater approximation. The calculations were performed with a $_Mn_{14}$ MO$_{56}$ )$^{-52}$ (M = transition metals) cluster model. The electron energy level, the density of states (DOS), the overlap population, the charge density distribution, and the net charges, were calculated. The energy level diagram of MnO$_2$ shows the different band structure and electron occupancy between the up spin states and down spin states. The dopant levels decrease between the conduction band and the valence band with the increase of the atomic number of dopants. The covalency of chemical bonding was shown to increase and ionicity decreased in increasing the atomic number of dopants. Calculated results were discussed on the basis of the interaction between transition metal 3d and oxygen 2p orbital. In conclusion it is expected that when the transition metals are added to MnO$_2$ the band gap decreases and the electronic conductivity increases with the increase of the atomic number of dopants. the atomic number of dopants.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.148-151
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• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.

• 한국재료학회지
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• 제12권11호
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• pp.860-864
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• 2002

$Li^{+}$ extraction reactions with ion-exchange type lithium manganese oxide in an aqueous phase were examined using chemical and x-ray diffraction (XRD) analysis. In the process of extraction reaction, the lithium manganese oxide showed a topotactic extraction of $Li^{+ }$ in the aqueous phase mainly through an ion-exchange mechanism, and the $Li^{+}$ extracted samples indicated a high selectivity and a large capacity for $Li^{+}$ . The electronic structures and chemical bonding properties were also studied using a discrete variational (DV)-X$\alpha$ molecular orbital method with cluster model of (Li$Mn_{12}$ $O_{40}$ )$^{27-}$ for tetrahedral sites and ($Li_{7}$ Mn $O_{38}$ )$^{3}$ for octahedral site in $Li_{1.33}$ $Mn_{1.67}$ / $O_{4}$ respectively. Li in the manganese oxides is highly ionized in both sites, but the net charge of Li was greater for tetrahedral sites than octahedral. These calculations suggest that the tetrahedral sites have higher $Li^{+}$ $H^{+}$ exchangeability than the octahedral sites, and are preferable for the selective adsorption for L $i^{+}$ ions.s.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1994년도 추계 학술발표 강연 및 논문 개요집
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• pp.1-1
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• 1994

;The electronic state calculations for various types of ceramic materials have beell performed by the use of $DV-X\;{\alpha}$ cluster method. The molecular orbital levels and wave functions for model clusters have been computed to study the electronic properties ami chemical bonding of the ceramics. For ${\beta}-sialon(Si_{6-z}Al_zO_zN_{8-z})$ which is a high temperature structural material based on ${\beta}-Si_3N_4$, we have made model cluster calculations to estimate the strength of chemical bonding between atoms by the Mulliken population analysis. It is found that the covalent bonding between Si and N atoms is very strong in pure ${\beta}-Si_3N_4$, but the covalency around solute atom is considerably weakened when Si atom is substituted by AI. This tendency is enhanced by an additional substitution of oxygen atom for N. The result calculated can well explain the experimental data of changes in mechanical properties such as the reductions of Young's modulus and Vickers hardness with increment of z-value in ${\beta}-sialon$. Various model clusters for transition metal oxides which show many interesting physical and chemical properties have also been calculated. High-valent perovskite-type iron oxides EMFe0_3E(M=Ca and Sr) possess very interesting magnetic and chemical properties. In these oxides, iron exists as $Fe^{4+}$ state, but the experimental measurement of Mossba~er effect suggests that disproportionation $2Fe^{4+}=Fe^{3+}+Fe^{5+}$ takes place for $CaFe0_3$ at low temperatures. The model cluster calculations for these compounds indicated the existence of considerably strong covalent bonding of Fe-O. The calculations of hyperfine interaction at iron neucleus show very good agreement with the experimental Mossbauer measurements. The result calculated also implies that the disproportionation reaction is strongly possible by assuming the quenching of breathing phonon mode at low temperatures.tures.

• 대한화학회지
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• 제43권2호
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• pp.206-212
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• 1999

본 연구의 목적은 기존의 $Zn_2SiO_4:Mn$형광체에 새로운 co-dopant를 첨가하여 발광특성을 향상시키는 것이다. co-dopant로서 선정한 Mg와 Cr이온들은 Zn자리를 치환하는 것으로 알려져 있으며 실제로 co-doping 시 각각 발광휘도와 decay time을 개선시키는 효과를 거두었다. $Zn_2SiO_4:Mn$에 Mg와 Cr이온들이 co-doping될 시에는 lattice 및 $Mn^{2+}$의 에너지 준위를 변화시키는 것으로 추정되어 발광휘도 및 decay time의 변화를 일으키는 것으로 해석된다. 특히 이 원소들은 발광과정에 긍정정인 영향을 끼쳐 Mg는 발광휘도를 중가시키고 Cr은 decay time을 감소시키는 결과를 얻었다. $Zn_2SiO_4:Mn,\;Mg$ 형광체의 발광휘도 개선은 DV-X${\alpha}$ embedded cluster 계산방법으로 설명할 수 있었고 반면에 $Zn_2SiO_4:Mn,\;Cr$ 형광체가 decay time을 줄이는 원인은 Mn이온과 Cr이온사이에 energy transfer가 일어나 발생되는 것으로 추정된다.