Browsing by Author "Gu, W"

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    Effects of penta- and trivalent dopants on structure and conductivity of Li7La3Zr2O12
    (Elsevier, 2015-06-01) Gu, W; Ezbiri, M; Prasada Rao, R; Avdeev, M; Adams, S
    Due to their high ionic conductivity and stability versus metallic lithium, garnet-related Li7La3Zr2O12 (LLZ) are of interest as Li+ solid electrolytes. The correlation between structure and ion mobility in undoped, Ta5 +, Nb5 +, Ga3 + or Al3 + doped LLZ is studied combining molecular dynamics (MD) simulations and experimental characterisation. Neutron and in situ XRD powder diffraction are employed to analyse the Li and dopant distribution and temperature dependence of the structure. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping Al3 + or Ga3 + on the Li site is slightly less effective in enhancing conductivity. Ga3 + doping on the La3 + site only helps to retain the cubic phase, but does not affect the mobile charge carrier concentration. The cooling rate after sintering is found to strongly affect both the ionic conductivity and its hysteresis on subsequent thermal cycling in the low temperature range, which can be attributed to local Li ordering as manifested by non-linear variations of the lattice parameters. © 2015 Elsevier B.V.
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    In situ neutron diffraction monitoring of Li7La3Zr2O12 formation: towards a rational synthesis of garnet solid electrolytes
    (American Chemical Society, 2015-04-01) Rao, RP; Gu, W; Sharma, N; Peterson, VK; Avdeev, M; Adams, S
    The favorable combination of fast-ionic conductivity and high electrochemical stability of Li-stuffed garnet type Li7La3Zr2O12 (LLZ) makes this material a promising candidate for applications as a solid-state electrolyte in high-energy-density batteries. However, a widespread technical use of LLZ is impeded by difficulty in reliable formation and densification of the pure fast-ion conducting phase. The present study of the phase-formation process enables rational fabrication procedures to be devised based on a thorough understanding of the complex phase formation of LLZ. In situ neutron powder diffraction monitoring of the phase formation revealed an influence of the partial melting of precursors on the formation of the fast-ion conducting phase, indicating that in the typical synthesis route LLZ is not formed in a solid-state reaction but from a partial carbonate melt that decomposes on further heating. The cooling rate critically influences lithium ordering and ionic conductivity. © 2015 American Chemical Society