• Korean Journal of Materials Research
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• v.23 no.2
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• pp.98-103
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• 2013

$Mg_{3-x}Zn_xSb_2$ powders with x = 0-1.2 were fabricated by mechanical alloying in a planetary ball mill with a speed of 350 rpm for 24 hrs and then hot pressed under a pressure of 70 MPa at 773 K for 2 hrs. It was found that there were systematic shifts in the X-ray diffraction peaks of $Mg_3Sb_2$ (x = 0) toward a higher angle with increasing Zn for both the powder and the bulk sample and finally the phase of $Mg_{1.86}Zn_{1.14}Sb_2$ was formed at the Zn content of x = 1.2. The $Mg_{3-x}Zn_xSb_2$ compounds had nano-sized grains of 21-30 nm for the powder and 28-66 nm for the hot pressed specimens. The electrical conductivity of hot pressed $Mg_{3-x}Zn_xSb_2$ increased with increasing Zn content and temperature from 33 $Sm^{-1}$ for x = 0 to 13,026 $Sm^{-1}$ for x = 1.2 at 323 K. The samples for all the compositions from x = 0 to x = 1.2 had positive Seebeck coefficients, which decreased with increasing Zn content and temperature, which resulted from the increased charge carrier concentration. Most of the samples had relatively low thermal conductivities comparable to the high performance thermoelectric materials. The dimensionless figure of merit of $Mg_{3-x}Zn_xSb_2$ was directly proportional to the Zn content except for the compound with Zn = 1.2 at high temperature. The $Mg_{3-x}Zn_xSb_2$ compound with Zn = 0.8 had the largest value of ZT, 0.33 at 723 K.

• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.262-267
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• 2010

$LiNi_{1-x}Mg_xO_2$(x=0, 0.025, 0.05, 0.075, 0.1) samples were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. $LiNi_{1-x}Mg_xO_2$samples give single phases of hexagonal layered structures with a space group of R-3m. The calculated cation-anion distances and angles from the Rietveld refinement were changed with Mg contents in $LiNi_{1-x}Mg_xO_2$. The thicknesses of $NiO_2$ slabs were increased and the distances between the $NiO_2$ slabs were decreased with the increase in Mg contents in the samples. The electrical conductivities of sintered $LiNi_{1-x}Mg_xO_2$ samples were around $10^{-2}$ S/cm at room temperature. The electrochemical performances of $LiNi_{1-x}Mg_xO_2$were evaluated by coin cell test. Compared to $LiNiO_2$, $LiNi_{0.95}Mg_{0.05}O_2$ exhibited improved high-rate capability and cyclability due to the well-ordered layered structure by doping of Mg ion.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.831-832
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• 2006

Solid-state processing via the bulk mechanical alloying enables us to directly fabricate $Mg_2X$ semi-conductive material performs. Precise control of chemical composition leads to investigation on the dilution and enrichment of X in $Mg_2X$. Two types of solid-state reactivity are introduced: e.g. synthesis of $Mg_2Si$ from elemental mixture Mg-Si is nucleation-controlled process while synthesis of $Mg_2Sn$ from Mg-Sn, diffusion-controlled process. Thermoelectricity of these $Mg_2X$ is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.75-76
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• 2006

New PM route via bulk mechanical alloying is developed to fabricate the solid solution semi-conductive materials with $Mg_2Si_{1-x}Ge_x$ and $Mg_2Si_{1-y}Sn_y$ for 0 < x, y < 1 and to investigate their thermoelectric materials. Since $Mg_2Si$ is n-type and both $Mg_2Ge$ and $Mg_2Sn$ are p-type, pn-transition takes place at the specified range of germanium content, x, and tin content, y. Through optimization of chemical composition, solid-solution type thermoelectric semi-conductive materials are designed both for n-and p-type materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.248-251
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• 1999

The microwave dielectric properties of The Dielectric Properties of $Ba_{1-x}$A$_{x}$(Mg$_{1}$3/Nb$_{2}$3/)O$_3$ (A = Sr, Ca, x = 0, 0.2 ,0.4 ,0.6, 0.8, 1.0) were investigated. In composition of $Ba_{1-x}$A$_{x}$(Mg$_{1}$3/Nb$_{2}$3/)O, densities are decreased with increasing x values. Grain sizes are decreased with Sr content and Increased with Ca content. The hexagonally ordered superstructure was observed in $Ba_{1-x}$Sr$_{x}$(Mg$_{1}$3/Nb$_{2}$3/)O$_3$(BSMN) systems, the intensity of superlattice increased with x value. In $Ba_{1-x}$Cr$_{x}$(Mg$_{1}$3/Nb$_{2}$3/)O$_3$(BSMN) systems, the additional diffraction patterns were shown. The highest value of $\varepsilon$$_{r}$ was shown in x=0.2 of BCMN systems and the value was 41.9. The highest Q$\times$f was shown in x=0.2 of BSMN systems and the value was 68,000. $\tau$$_{f}$ were shown 0 ppm/$^{\circ}C$ near x=0.8.TEX> near x=0.8.0.8.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.840-845
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• 2004

The microstructure and microwave dielectric properties of $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics were investigated. The specimens were prepared by the conventional mixed oxide method with sintering temperature of 140$0^{\circ}C$∼150$0^{\circ}C$. To improve the quality factor and the temperature coefficient of resonant frequency,$ Ti{O}_2(\varepsilon\Gamma=100, Q\times f_\Gamma=40,000 GHz,\ta_f= +450 ppm\diagup^{\circ}C $ was added in ${Mg}_4{Ta}_2{O}_9$ceramics. The dielectric and structural properties were investigated. According to the XRD patterns, $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics had the ${Mg}_4{Ta}_2{O}_9$ phase(hexagonal) and ${MgTi}_2{O}_5$phase(orthorhombic). The dielectric constant($\varepsilon_r$). quality($Qtimes{f}_r$${\tau}_f$) of the $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics were 8.12∼18.59, 18,750∼186,410 GHz and －36.02∼＋3.46 ppm/$^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.280-286
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• 2001

10 이하의 저유전율을 갖는 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스의 미세구조와 고주파 유전특성을 조사하였다. (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스는 정방정(tetragonal) 구조를 가진다. 0.1BaWO$_4$-0.9Mg$_2$SiO$_4$세라믹스는 BaWO$_4$와 $Mg_2$SiO$_4$의 상들이 공존하는 혼합상을 보였으며, $Mg_2$SiO$_4$가 이차사으로 형성된 것이 관찰되었다. 120$0^{\circ}C$~140$0^{\circ}C$에서 2시간 동안 소결된 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x=0.1~0.9) 세라믹스는 $\varepsilon$$_{r}$=6.37~8.21, Q.f=15000~99422 그리고 $ au$$_{f}$=73.9~48.9 ppm/$^{\circ}C$의 고주파 유전특성을 가졌다. $\tau$$_{f}$를 보정하기 위해, CaTiO$_3$(1,5 wt%)가 (1-x)BaWO$_4$-xMg$_2$SiO$_4$(x$\geq$0.9) 세라믹스에 첨가되었다. 135$0^{\circ}C$에서 2시간 동안 소결된 0.1BaWO$_4$-0.9Mg$_2$SiO$_4$+CaTiO$_3$(5 wt%) 세라믹스는 $\varepsilon$$_{r}$=7.3, Q.f=30532 그리고 $\tau$$_{f}$=-30 ppm/$^{\circ}C$의 고주파 유전특성을 얻었다. 얻었다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.7
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• pp.344-348
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• 2006

The effect of x on microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics for microwave components were investigated. All spcecimens prepared by the conventional mixed oxied method and sintered at $1450^{\circ}C$. Microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-xTiO_2$ ceramics were influenced by $MgTi_2O_5$ phase. Also the microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were dominated with an addition of $CaTiO_3\;and\;SrTiO_3$. The dielectric constant $(\varepsilon_r)$, quality factor $(Q{\times}f_r)$ and temperature coefficient of the resonant frequency $(TCRF,\;\tau_f)$ of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were $12.96\sim70.98,\;5,132\sim186,410GHZ$ and $-35.82\sim+75.96ppm/^{\circ}C$, respectively, and depend on x and addition materials.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.1
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• pp.6-13
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• 2001

By using a vertical Bridgeman method, single crystalline structures of $Mg_xZn_{1-x}Te(0{\le}X{\le}0.48)$ were grown for various Mg mole compositions. With the increasing Mg fraction, the lattice constant is linearly increased from 6.103 to 6.239$\AA$ for the range of $0{\le}X{\le}0.48$ and the lattice constant of zincblende MgTe was linearly extrapolated to the value of 6.433$\pm$0.002$\AA$. The optical properties of the crystalline structure were characterized with photocurrent measurements. As a results of photocurrent spectra, the single crystalline $Mg_xZn_{1-x}Te$ show the energy bandgap of 2.380 and 2.260eV at 4.2 and 294 K, respectively. The photocurrent peak blueshifts with increasing Mg mole fraction and show the linear dependence of energy bandgap, $E_g$(X)=b+(0.8)X. The extrapolation shows the energy bandgaps of MgTe of 3.18 and 3.06eV at the temperatures of 4.2 and 294K, respectively. Furthermore, the photocurrent peaks redshifts with increasing temperature and the temperature coefficient is given to the value of $dE_g$/dT=-(5.6~$6.1){\times}10^{-4}$eV/K. for the temperature range above 100K.

• Journal of Korea Foundry Society
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• v.31 no.6
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• pp.362-365
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• 2011

In the present work, the corrosion properties of Mg-xSn (x = 1, 3, 5, 7 and 9 wt.%) alloys have been investigated. Potentiodynamic polarization and immersion tests were carried out in 3.5% NaCl solution of pH 7.2 at room temperature to measure the corrosion properties of Mg-xSn (x = 1, 3, 5, 7 and 9 wt.%) alloys. With increase of the Sn contents, the volume fraction of the $Mg_2Sn$ phase was increased. The corrosion rate of Mg-xSn alloys was increased up to 7 wt.%Sn and decreased above 9 wt.%Sn. Initiation of galvanic site during immersion mainly occurred at Mg/$Mg_2Sn$ interface and propagation went into ${\alpha}$-Mg. For this reason, corrosion properties of Mg-xSn (added from 1 wt.%Sn to 7 wt.%Sn alloys) alloys are decreased because the galvanic site was increased with increasing Sn addition. In Mg-9wt.%Sn alloy, however, the corrosion site were changed from Mg/$Mg_2Sn$ interface to ${\alpha}$-Mg/$M_2Sng$ interface in lamellar structure. Preferentially corrosion of ${\alpha}$-Mg/$M_2Sn$ interface in lamellar structure impeded corrosion propagation went into ${\alpha}$-Mg.