• Title/Summary/Keyword: nonstoichiometric

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Proton Conduction in Nonstoichiometric Σ3 BaZrO3 (210)[001] Tilt Grain Boundary Using Density Functional Theory

  • Kim, Ji-Su;Kim, Yeong-Cheol
    • 한국세라믹학회지
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    • 제53권3호
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    • pp.301-305
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    • 2016

  • We investigate proton conduction in a nonstoichiometric ${\Sigma}3$ $BaZrO_3$ (210)[001] tilt grain boundary using density functional theory (DFT). We employ the space charge layer (SCL) and structural disorder (SD) models with the introduction of protons and oxygen vacancies into the system. The segregation energies of proton and oxygen vacancy are determined as -0.70 and -0.54 eV, respectively. Based on this data, we obtain a Schottky barrier height of 0.52 V and defect concentrations at 600K, in agreement with the reported experimental values. We calculate the energy barrier for proton migration across the grain boundary core as 0.61 eV, from which we derive proton mobility. We also obtain the proton conductivity from the knowledge of proton concentration and mobility. We find that the calculated conductivity of the nonstoichiometric grain boundary is similar to those of the stoichiometric ones in the literature.

  • https://doi.org/10.4191/kcers.2016.53.3.301 인용 PDF KSCI

비화학양론적 Na+β-alumina를 위한 Mg 원자의 치환: 제일원리 계산 (Mg Atom Substitution for Nonstoichiometric Na+ β-Alumina: A First Principles Study)

  • 김대현;김대희;정용찬;서화일;김영철
    • 한국재료학회지
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    • 제20권2호
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    • pp.55-59
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    • 2010

  • $Na^+$ 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.

  • https://doi.org/10.3740/MRSK.2010.20.2.55 인용 PDF KSCI

Effect of Zinc Vacancy on Carrier Concentrations of Nonstoichiometric ZnO

  • Kim, Eun-Dong;Bahng, Wook
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2001년도 춘계학술대회 논문집 반도체재료
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    • pp.17-21
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    • 2001

  • We proposed that concentrations of cartier electron as well as ionized donor defects in nonstoichiometric ZnO are proportional to $P^{-1/2}_{O_2}$, whenever they ionizes singly or doubly, by employing the Fermi-Dirac (FD) statistics for ionization of the native thermal defects $Zn_i$ and $V_o$. The effect of acceptor defect, zinc vacancy $V_{Zn}$made by the Frenkel and Schottky disorder reactions, on carrier concentrations was discussed. By application of the FD statistics law to their ionization while the formation of defects is assumed governed by the mass-action law, the calculation results indicate; 1. ZnO shows n-type conductivity with $N_D>$N_A$ and majority concentration of $n{\propto}\;P^{-1/2}_{O_2}$ in a range of $P_{O_2}$, lower than a critical value. 2. As the concentration of acceptor $V_{Zn}$ increases proportional to $P^{1/2}_{O_{2}}$, ZnO made at extremely high $P_{O_{2}}$, can have p-type conductivity with majority concentration of p ${\propto}\;P^{-1/2}_{O_{2}}$. One may not, however, obtain p-type ZnO if the pressure for $N_{D}<$N_{A}$ is too high.

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Study of Nonstoichiometry and Physical Properties of the $Nd_{1-x}(Ba_{0.40}Mg_{0.60})_{1+x}FeO_{4-y}$ System

  • 요철현;노권순;장순호
    • Bulletin of the Korean Chemical Society
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    • 제16권3호
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    • pp.261-264
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    • 1995

  • A series of samples of the Nd1-x(Ba0.40Mg0.60)1+xFeO4-y (x=0.00, 0.10, 0.20, and 0.30) system has been synthesized at 1450 ℃ under an atmospheric air pressure. The x-ray powder diffraction analysis of the solid solutions assigns the structure of all the compositions to orthorhombic system. Mohr salt analysis shows that τ and y values increase with x value and nonstoichiometric chemical formulas of the system can be formulated from the x, τ, and y values. Oxygen vacancies are distributed along c-axis in the perovskite layer. The magnetic ordering temperature remains unchanged with x value. Electrical conductivity and activation energy depend only on the mixed valence state of Fe ion. Conduction mechanism can be suggested as the hopping of electron between eg orbitals of Fe3+ and Fe4+ ions through Fe3+-O-Fe4+ bonds. Magnetic susceptibility and electrical conductivity are discussed with the nonstoichiometric chemical formulas.

  • https://doi.org/10.5012/bkcs.1995.16.3.261 인용 PDF