Browsing by Author "Moon, KH"

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    Crystal structure and optical property of complex perovskite oxynitrides ALi0.2Nb0.8O2.8N0.2, ANa0.2Nb0.8O2.8N0.2, and AMg0.2Nb0.8O2.6N0.4 (A = Sr, Ba)
    (Elsevier, 2017-10-01) Moon, KH; Avdeev, M; Kim, YI
    Oxynitride type complex perovskites AM0.2Nb0.8O3−xNx (A = Sr, Ba; M = Li, Na, Mg) were newly synthesized by the solid state diffusion of Li+, Na+, or Mg2+ into the layered oxide, A5Nb4O15, with concurrent O/N substitution. Neutron and synchrotron X-ray Rietveld refinement showed that SrLi0.2Nb0.8O2.8N0.2, SrNa0.2Nb0.8O2.8N0.2, and SrMg0.2Nb0.8O2.6N0.4 had body-centered tetragonal symmetry (I4/mcm), while those with A = Ba had simple cubic symmetry (Pm ̅ m). In the tetragonal Sr-compounds, the nitrogen atoms were localized on the c-axial 4a site. However, the octahedral cations, M/Nb (M = Li, Na, Mg) were distributed randomly in all six compounds. The lattice volume of AM0.2Nb0.8O3−xNx was dependent on various factors including the type of A and the electronegativity of M. Compared to the simple perovskites, ANbO2N (A = Sr, Ba), AM0.2Nb0.8O3−xNx had wider band gaps (1.76–2.15 eV for A = Sr and 1.65–2.10 eV for A = Ba), but significantly lower sub-gap absorption. © 2017 Elsevier Inc.
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    Crystal structures and color properties of new complex perovskite oxynitrides AMg0.2Ta0.8O2.6N0.4 (A = Sr, Ba)
    (Royal Society of Chemistry, 2016-02-26) Moon, KH; Kim, JM; Sohn, Y; Cho, DW; Kim, YI; Avdeev, M
    New complex perovskite oxynitrides AMg0.2Ta0.8O2.6N0.4 (A = Sr, Ba) were synthesized by reacting A5Ta4O15 with MgCl2 in flowing NH3. The formation of AMg0.2Ta0.8O2.6N0.4 can be described as the cooperative insertion of Mg2+ + 2N3− and the release of 2O2− from the layered oxide, A5Ta4O15. Rietveld refinement of the neutron and synchrotron X-ray diffraction patterns indicated that BaMg0.2Ta0.8O2.6N0.4 is simple cubic (Pm[3 with combining macron]m) and SrMg0.2Ta0.8O2.6N0.4 is body-centered tetragonal (I4/mcm), isostructural with BaM0.2Ta0.8O2.8N0.2 and SrM0.2Ta0.8O2.8N0.2 (M = Li, Na), respectively. The nitrogen in SrMg0.2Ta0.8O2.6N0.4 is partially ordered favoring the c-axial site over the ab-plane of the tetragonal cell, which is a different O/N order pattern from that of SrLi0.2Ta0.8O2.8N0.2 and SrNa0.2Ta0.8O2.8N0.2. The group of simple and complex perovskites, ATaO2N, ALi0.2Ta0.8O2.8N0.2, ANa0.2Ta0.8O2.8N0.2, and AMg0.2Ta0.8O2.6N0.4 (A = Sr, Ba) covers the band gap range, 1.9–2.4 eV, and the color ranges from yellow to dark brown. © Royal Society of Chemistry 2021