• Journal of Magnetics
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• v.12 no.3
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• pp.97-102
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• 2007

We have investigated the electronic structures and magnetism of a full Heusler alloy $Co_2CrGa(001)$ surface by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered two types of different terminations: the Co-terminated (Co-Term) and the CrGa-terminated (CrGa-Term) surfaces. From the calculated layer-projected density of states (LDOS), we found that the surface of the CrGa-Term shows nearly half-metallic character while that of the Co-Term is far from the half-metallic. For the Co-Term, the surface Co atom moves down to the bulk region by $0.05{\AA}A$, while the subsurface Cr and Ga atoms move up to the surface layer by 0.05 and $0.01{\AA}$, respectively. For the CrGa-Term, there is a large inward relaxation of the surface Ga atom $(0.07{\AA})$, but the relaxation of the surface Cr atom is very small $(0.01{\AA})$. The relaxations affect not much to the overall shapes of DOS for both terminations, but make the surface states of the surface Cr and Ga atoms for the CrGa-Term shift to higher energy that enhances the nearly half-metallic character of the CrGa-Term. The magnetic moments of the surface $Cr(2.98{\mu}_B)$ in the CrGa-Term and the surface $Co(1.17{\mu}_B)$ in the Co-Term were much increased compared to those of the inner-layers $(1.79\;and\;0.77{\mu}_B)$, respectively, while that of the subsurface Cr atom in the Co-Term was decreased to $1.19{\mu}_B$.

• Journal of the Korean Magnetics Society
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• v.25 no.2
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• pp.31-38
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• 2015

Recently, a first-principles study led to a prediction that quaternary Heusler compounds, CoFeCrZ (Z = Ga, Ge) are excellent half-metallic ferromagnets. In this study, we investigate the electronic and the magnetic properties at the (001) surfaces of CoFeCrGa and CoFeCrGe by means of the full-potential linearized augmented plane wave (FLAPW) method within generalized gradient approximation. We considered two types of surface termination: CoFe-terminated and CrZ-terminated surfaces, Z being either Ga or Ge. From the calculated total magnetic moments and the local density of states, we found that half-metallicity is not preserved for all the surfaces. But the calculated atomic density of states showed that CrGa-terminated surface of the CoFeCrGa is almost half-metallic. The magnetic moment of the Co, Fe, or Cr atoms at the surface or subsurface layers in each system had very different values.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.1
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• pp.83-91
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• 1994

We have constructed a vertical gradient freeze (VGF) grower for GaAs single crystals 2 inch in diameter and have grown semi-insulating GaAs co-doped with Cr and In. For the co-doped crystal, the segregation coefficients of the dopants remain unchanged when compared to those doped with only Cr or In. The concentration of Cr and in atoms range from about $2{\Times}10_{16} to 3{imes}10^{17} cm^{-3}$ and $2{\Times}10^{19} to 3{\Times}10^{20} cm^{-3}$ at the seed to the tail part of the grown crystal, respectively. The averaged dislocation etch pit density is found to be less than $8000 cm^{-2}$ throughout the ingot. It is also found that there is some evidence of lattice hardening for the crystal in which the dislocation density is decreased to less than $1000 cm^{-2}$ as In concentration increases. The resistivity increases abruptly from $10^{-2}$ up to $10^8$ Ohm-cm, while the carrier concentration decreases from $10^{16}$ to $10^8 cm^{-3}$ along the growth direction of the GaAs crystal. Semi-insulating properties can be obtained above a critical concentration of Cr of about $6{\Times}10{^16} cm^{-3}$ in the crystal. The main deep levels existing in the GaAs: Cr,In sample are two electron traps at $E_C-0.81eV, E_C-0.35eV$, and two hole traps at $E_V+0.89eV, E_V+0.65eV$.

• Bulletin of the Korean Chemical Society
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• v.19 no.4
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• pp.466-470
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• 1998

Catalytic hydrogenation of carbon dioxide for the simultaneous synthesis of methanol and dimethyl ether (together called oxygenates) over a combination of methanol synthesis and methanol dehydration catalysts has been studied. Various methanol synthesis and methanol dehydration catalysts were examined for this reaction. The addition of promotors like $Ga_2O_3\; and\; Cr_2O_3$ to Cu/ZnO catalyst gave much more enhanced yield on the formation of oxygenates. From the results, the promotional effect of $Cr_2O_3$ has been explained in terms of increase in the intrinsic activity of Cu while that of $Ga_2O_3$ being increase in the dispersion of Cu. Among the methanol dehydration catalysts examined, the solid acids bearing high population of intermediate-strength acid sites were found to be very effective for the production of oxygenates. HY zeolite which contains strong acid sites produce small amount of hydrocarbons as by-products. However, CuNaY zeolite in which the presence of strong acid sites are minimum gives very high oxygenates yield without the formation of hydrocarbons.

• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.816-820
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• 2005

The doped-ceria is a strong candidate material for an intermediate temperature SOFC. However, the mechanical strength and the magnitude of electrical conductivity need to be increased at low sintering temperature. In this study, to improve both properties, $1at\% $ of Mg, Ca, Cr, Fe, Co, Ni, Cu, Ga, and Zr were added to the GDC20 ($20at\%$ Gd-doped Ceria) and sintered at $1350^{\circ}C$ that is $250^{\circ}C$ lower than $1600^{\circ}C$. With addition, the relative density of the sintered sample increased. Fe, Co, Ni, Cu, Ga doped-GDC20 showed high relative density over $92\%$. Among them, Ga doped-GDC20 showed the most improved sinterability. The conductivity of doped­GDC20 increased by $\~10$ times at $300\~700^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.715-719
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• 2007

STS444 with or without $La_{0.9}Sr_{0.1}MnO_3$ (LSM)-coating was contacted to $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$ (LSCF) cathode on various electrolyte materials and the polarization resistance $(R_p)$ was measured by impedance spectroscopy. By making a symmetric half-cell and contacting only one side of the cathode with the interconnect, the effect of chromium (Cr) poisoning was separated from the aging effects. When the LSCF cathode was contacted with LSM-coated STS (stainless steel), $R_p$ of LSCF was lower than that contacted with the uncoated STS. Impedance patterns measured for the working electrode (W.E.), the counter electrode (C.E.) at $600^{\circ}C$ in air were analyzed. Normalized data of net Cr effect showed that $Ce_{0.9}Gd_{0.1}O_2$ (GDC) electrolyte is more tolerant to the chromium poisoning than $La_{0.9}Sr_{0.1}Ga_{0.8}Mg_{0.2}$ (LSGM) or 8 mol% $Y_2O_3-doped$ $ZrO_2$ (YSZ) electrolytes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.84-91
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• 2002

The stochiometric composition of $AgGaS_2$/GaAs polycrystal source materials for the $AgGaS_2$/GaAs epilayer was prepared from horizontal furnace. From the extrapolation method of X-ray diffraction patterns it was found that the polycrystal $AgGaS_2$/GaAs has tetragonal structure of which lattice constant an and Co were 5.756 $\AA$ and 10.305 $\AA$, respectively. $AgGaS_2$/GaAs epilayer was deposited on throughly etched GaAs(100) substrate from mixed crystal $AgGaS_2$/GaAs by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $590^{\circ}C$ and $440^{\circ}C$ respectively. The crystallinity of the grown $AgGaS_2$/GaAs epilayer was investigated by the DCRC (double crystal X-ray diffraction rocking curve). The optical energy gaps were found to be 2.61 eV for $AgGaS_2$/GaAs epilayer at room temperature. The temperature dependence of the photocurrent peak energy is well explained by the Varshni equation, then the constants in the Varshni equation are given by $\alpha=8.695{\times}10^{-4}$ eV/K, and $\beta=332K$. From the photocurrent spectra by illumination of polarized light of the $AgGaS_2$/GaAs epilayer, we have found that crystal field splitting ${\Delta}Cr$ was 0.28 eV at 20 K. From the PL spectra at 20 K, the peaks corresponding to free and bound excitons and a broad emission band due to D-A pairs are identified. The binding energy of the free excitons are determined to be 0.2676 eV and 0.2430 eV and the dissociation energy of the bound excitons to be 0.4695 eV.

• Korean Journal of Plant Resources
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• v.3 no.2
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• pp.107-114
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• 1990

In view of the results to have measured metallic elements which is included in 45 sorts of herb medicines and surveyed their distribution, 8 kinds ofmetals including Co, Ge, Ga, TL, Cd, As, 8i, Pb, are never or little includedin almost herb medicines . Other twenty-five sorts of elements (Mo, Sc, Be, V,Ni, Sn, Se, Ba, Cr, Sb, Si, Ti, B, Li, Mg, Ca, Cr, Mn, Fe, Cu, Zn, p, Al, Na,K) are more or Less included in all herb Bedicines ana Na, Ca, p and K aremetals that are included in Large quentities in comrarison with others . Patri-uiae Radix Contains 7 kinds of metal lic elements more than other herb medicinesdoes .

• Korean Journal of Plant Resources
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• v.3 no.2
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• pp.115-121
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• 1990

In view of the results to have measured metallic elements which is included in 40 sorts of herb medicines and surveyed their distribution, ninekinds of metals including Co, Ce, Ga, 71, Cd, As, Sbr Bu. Pb, are never orlittle included in almost herb medicines. Other twenty four sorts of ele-ments (Mo, Sc, Be, V, Ni, Su, Se, Ba, Cr, Su, Ti, B, Li, Mg, Ca, Sr, Mnl Fe,Cu, Zn. p, Al, Na, K) are metals that are included in large quentities incomparison with others. Selagirellae Radix contains is kinds of metallicelements more then other herb medicines does. The content of elements ofinorganic metal differs greatly according to the part of herb medicines .

• Korean Journal of Plant Resources
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• v.4 no.2
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• pp.39-45
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• 1991

Proximate compositions of the roots of cultured and wild Codonopsis lanceolata were examined as tile basic reasearch for the study of their source of processed foods.No significant difference in the contents was found between the wild root and thecultivated at 3$0^{\circ}C$ in biotronroom. In view of the results to have measured mineralswhich is included in 14 sorts of Codonopsis lanceolata and surveyed their distribution.12 kinds of minerals including T1, Co, Ge, Sm, Mo, Sc, Be, Cd, As, Ga, Bi, ph are ne-vel or little included in almost source. Other twenty-one sorts of minerals (Ni, Se,Ba, Sb, Si, Ti, B, Li, Ifs, Ca, Sr, Mn, Fe, Cu, Zn, p, Al, Na, V, Cr, K) are more or less in-cluded in all source and Ca, Mg, p, K, and Fe are metals that are included in large qu-entities in comparison with others. No minerals difference in the contents was foundbetween the cultivated temperature. The content of elements of inorganic metal differsaccording to the part of C. lanceolata.