Browsing by Author "Zhang, T"

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    Immobilization of Na ions for substantial power factor enhancement: site-specific defect engineering in Na0.8CoO2
    (American Chemical Society, 2012-02-16) Tsai, PH; Assadi, MHN; Zhang, T; Ulrich, C; Tan, TT; Donelson, R; Li, S
    Simultaneous enhancement of the interdependent Seebeck coefficient and electrical conductivity has been achieved through defect engineering by doping Mg into specific sites of Na0.8CoO2. Results from thermoelectric measurement demonstrate that the power factor was substantially increased by 50% at ambient. Experimental and theoretical analyses show that the occupation of divalent Mg in the disordered Na layer immobilizes the Na ions and thus induces a long-range ordering of Na ions. This phenomenon improves the carrier mobility significantly, giving rise to the observed exotic thermoelectric performance. Moreover, it is predicted that other electronically closed-shell dopants in sodium cobaltate play a similar role in enhancing the thermoelectric conversion efficiency. © 2012, American Chemical Society.
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    Using neutron diffraction to explore lithium displacement within cubic phase stabilised Ga-doped Li6.75La3Zr1.75Ta0.25O12 lithium garnet oxides
    (Elsevier, 2023-12-15) Christopher, TD; Zhang, T; Huang, S; Zujovic, Z; Avdeev, M; Cao, P; Söhnel, T
    Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY licence.