Browsing by Author "Wang, R"

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    A3A′3Zn6Te4O24 (A = Na, A′ = rare earth) garnets: A-site ordered noncentrosymmetric structure, photoluminescence, and Na-ion conductivity
    (American Chemical Society, 2021-11-16) Fang, Z; Jiang, P; Avdeev, M; Wei, H; Wang, R; Jiang, X; Yang, T
    A large number of oxides that adopt the centrosymmetric (CS) garnet-type structure (space group Ia3̅d) have been widely studied as promising magnetic and host materials. Hitherto, no noncentrosymmetric (NCS) garnet has been reported yet, and a strategy to NCS garnet design is therefore significant for expanding the application scope. Herein, for the series A3A′3Zn6Te4O24 (A = Na, A′ = La, Eu, Nd, Y, and Lu), we demonstrated that the structural symmetry evolution from CS Ia3̅d (A′ = La) to NCS I4122 (A′ = Eu, Nd, Y, and Lu) could be achieved due to the A-site cationic ordering-driven inversion symmetry breaking. Na3A′3Zn6Te4O24 (A′ = rare earth) are the first garnets that possess NCS structures with A-site cationic ordering. Diffuse reflectance spectra and theoretic calculations demonstrated that all these NCS garnets are indirect semiconductors. Moreover, their potential applications as host materials for red phosphors and Na-ion conductors were also investigated in detail, which firmly confirmed the NCS structure and A-site cationic ordering. Our findings have paved the way to design NCS or even polar garnets that show intriguing functional properties, such as ferroelectricity, multiferroicity, and second harmonic generation. © 2021 American Chemical Society
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    Optimizing the structure of layered cathode material for higher electrochemical performance by elucidating structural evolution during heat processing
    (Elsevier, 2020-12-01) Huang, ZY; Chu, MH; Wang, R; Zhu, WM; Zhao, WG; Wang, CQ; Zhang, YJ; He, LH; Chen, J; Deng, SH; Mei, LW; Kan, WH; Avdeev, M; Pan, F; Xiao, YG
    Improving electrochemical performance of cathode materials for lithium-ion batteries requires comprehensive understanding of their structural properties which could facilitate or impede the diffusion of lithium during charge-discharge. In order to optimize the structure and improve the electrochemical performance of layered cathode material, the detailed structural evolution as a function of heat treatment temperature in LiNi0.8Co0.1Mn0.1O2 was investigated by in-situ and ex-situ neutron powder diffraction methods. We show that both cycling stability and rate performance of LiNi0.8Co0.1Mn0.1O2 can be improved by performing heat treatment at 400 °C, which is attributed to the optimization of surface structure and the enlargement of c/a ratio. Heat treatment of LiNi0.8Co0.1Mn0.1O2 at higher temperature induces a layered-to-rock-salt structure phase transition accompanied with the precipitation of lithium oxide. A 3D phase diagram, which correlates the high temperature phases and room temperature phases, is constructed. The presentation of comprehensive phase diagrams up to 1000 °C could provide the basis for further research on not only synthesis strategy but also thermal stability in Ni-rich layered cathode materials. © 2020 Elsevier Ltd.