Browsing by Author "Lee, JF"

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    Studying the effects of Zr-doping in (Bi0.5Na0.5)TiO3 via diffraction and spectroscopy
    (Royal Society of Chemistry, 2014-10-13) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Zhang, Z; Avdeev, M; Jang, LY; Lee, JF; Pao, CW; Chen, JL
    The structural properties of (Bi0.5Na0.5)Ti1−xZrxO3 (where 0 ≤ x ≤ 0.7) have been investigated using powder diffraction and X-ray absorption spectroscopy. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Doping small amounts of Zr into the B site of (Bi0.5Na0.5)TiO3 initially stabilizes the rhombohedral phase before the orthorhombic Pnma phase begins to form at x = 0.5. Analysis of the Ti K-edge and Zr L3-edge XANES spectra show that the crystallographic phase change has very little effect on the local structure of Ti4+/Zr4+ cations, suggesting that there is little change in the cation off-center displacement within the BO6 octahedra with each successive phase change. © The Royal Society of Chemistry 2014
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    Vanadium substitution of LiFePO4 cathode materials to enhance the capacity of LiFePO4-based lithium-Ion batteries
    (American Chemical Society, 2012-11-22) Chiang, CY; Su, HC; Wu, PJ; Liu, HJ; Hu, CW; Sharma, N; Peterson, VK; Hsieh, HW; Lin, YF; Chou, WC; Lee, CH; Lee, JF; Shew, BY
    The mechanism of enhancing the capacity of the LiFePO(4) cathodes in lithium ion batteries by the addition of a small amount of vanadium, which locate on the lithium site and induce lithium vacancies in the crystal structure, is reported in this article. As a result, the capacity increases from 138 mAh/g found for pristine LiFePO(4) to 155 mAh/g for the V-added compound, and the conductivity increases from 4.75 x 10(-4) S/cm for the LiFePO(4) without V addition to 1.9 x 10(-2) S/cm for the V-added compound. A possible model to facilitate the enhancement of conductivity and capacity is described with evidence supported by X-ray powder diffraction, X-ray absorption spectroscopy, and neutron powder diffraction data. © 2012, American Chemical Society.