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- 주제어 : Mg substitution (검색결과 5 건)
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비화학양론적 Na<sup>+</sup>β-alumina를 위한 Mg 원자의 치환: 제일원리 계산
김대현,김대희,정용찬,서화일,김영철,Kim, Dae-Hyun,Kim, Dae-Hee,Jeong, Yong-Chan,Seo, Hwa-Il,Kim, Yeong-Cheol 한국재료학회 2010 한국재료학회지 Vol.20 No.2
$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.
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Kim, Chungman,Kim, Soohyun,Hong, Yang-Ki,Oh, Min-Wook,Jung, Myung-Hwa Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.690 No.-
<P><B>Abstract</B></P> <P>Single crystals of Mg<SUB>2−<I>x</I> </SUB>Mn<SUB> <I>x</I> </SUB>Si (<I>x</I> = 0, 0.1, 0.2, 0.3, and 0.4) were prepared using a vertical Bridgman method. The formation of desired materials was confirmed using single-crystal and powder X-ray diffraction. The thermoelectric and magnetic properties were investigated for various Mn contents in the temperature range between 2 and 300 K and in magnetic fields up to 70 kOe. For various <I>x</I> values, Mg<SUB>2−<I>x</I> </SUB>Mn<SUB> <I>x</I> </SUB>Si with <I>x</I> = 0.2 possesses the highest figure of merit. The experimental results revealed that the substitutional Mn atoms exhibit mixed valences of +3 (majority) and +2, giving rise to dramatic changes of carrier density and magnetic interaction. At the same time, the Seebeck coefficient and magnetic susceptibility show a sudden change at the same temperature. These results imply that the thermoelectric properties are correlated with the magnetic properties in the Mg<SUB>2−<I>x</I> </SUB>Mn<SUB> <I>x</I> </SUB>Si crystals.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Single crystals of Mg<SUB>2−x</SUB>Mn<SUB>x</SUB>Si were prepared by using a vertical Bridgman method. </LI> <LI> The thermoelectric performance was improved as doping Mn into Mg<SUB>2</SUB>Si. </LI> <LI> The magnetic properties were enhanced with Mn dopants. </LI> <LI> The thermoelectric and magnetic properties were strongly correlated in Mg<SUB>2−x</SUB>Mn<SUB>x</SUB>Si. </LI> </UL> </P>
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Na-Ion Anode Based on Na(Li,Ti)O<sub>2</sub> System: Effects of Mg Addition
Kim, Soo Hwa,Bae, Dong-Sik,Kim, Chang-Sam,Lee, June Gunn The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.3
This study involves enhancing the performance of the $Na(Li,Ti)O_2$ system as an Na-ion battery anode with the addition of Mg, which partially replaces Li ions. We perform both computational and experimental approaches to achieve a higher reversible capacity and a faster transport of Na ions for the devised system. Computational results indicate that the $Na(Li,Mg,Ti)O_2$ system can provide a lower-barrier path for Na-ion diffusion than can a system without the addition of Mg. Experimentally, we synthesize various $Na_z(Li_y,Mg_x,Ti)O_2$ systems and evaluate their electrochemical characteristics. In agreement with the theoretical study, Mg addition to such systems improves general cell performance. For example, the prepared $Na_{0.646}(Li_{0.207}Mg_{0.013}Ti_{0.78})O_2$ system displays an increase in reversible capacity of 8.5% and in rate performance of 13.5%, compared to those characteristics of a system without the addition of Mg. Computational results indicate that these improvements can be attributed to the slight widening of the Na-$O_6$ layer in the presence of Mg in the $(Li,Ti)O_6$ layer.
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Dielectric Characteristics of BaTiO3 Solid Solution Substituted with Nb5+, Ta5+, Bi3+, and Sb3+ Ions
김연중 한국진공학회 2023 Applied Science and Convergence Technology Vol.32 No.5
The structural and electrical properties of ferroelectrics can be altered through different mechanisms to meet necessary conditions, depending on the additive type in appropriate proportions. This study investigates the growth process of four types of BaTiO3 (BT), each substituted with 0.1 mol% of trivalent and pentavalent elements: Nb5+, Ta5+, Bi3+, and Sb3+. The relationship between the dielectric properties of perovskite formation and grain growth is explored across the four dopants. The results confirm the proficient growth of these four BT compositions when substituted with trivalent and pentavalent ions, yielding relatively high-density particles. Moreover, the fundamental dielectric properties of the ferroelectrics satisfied the required levels. X-ray diffraction studies revealed that both Nb- and Ta-doped BT, prepared by substituting 0.1 mol% of Nb5+ and Ta5+, demonstrated distinctive splitting of the (200) and (002) peaks within the range of 45.10–45.45∘. However, no clear evidence was observed for Bi- and Sb-doped BT compositions containing trivalent Bi3+ and Sb3+ ions. In particular, the transition temperature of the four substituted BT compositions exhibited negligible divergence from that of pure BT, with a marginal shift toward lower temperatures. In addition, contrary to pure BT, the characteristics of ln(T-Tm) vs. ln[(1/K)-(1/Km)] and 1/K vs. T, which elucidate high-temperature phase transitions, exhibited relatively well-satisfied behavior with the modified Curie–Weiss law.
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Alam Mohammad Mujahid,Atkore Sandeep T.,Kamble Vinod T.,Varala Ravi 대한화학회 2022 Bulletin of the Korean Chemical Society Vol.43 No.4
This work describes the highly efficient acetylation (acylation) of alcohols with acetic acid for the ester synthesis in the presence of newly designed a new composite zirconium (IV) chloride and magnesium catalyst which is used bimetallic acidic catalyst ZrCl4-Mg(ClO4)2, which is formed by grinding ZrCl4 and Mg(ClO4)2 in the molar ratio of 1:2, respectively. Thus, the powder X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller surface area, and thermogravimetric analysis of the ZrCl4, Mg(ClO4)2, and non-calcined ZrCl4-Mg (ClO4)2 were recorded. In each case, structural analysis was carried by grinding the catalyst in mortar and pestle.
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