Zeier Wolfgang G, Zhou Shiliang, Lopez-Bermudez Beatriz, Page Katharine, Melot Brent C
Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
ACS Appl Mater Interfaces. 2014 Jul 23;6(14):10900-7. doi: 10.1021/am4060194. Epub 2014 Mar 26.
Inspired by the promising ionic conductivities of the lithium conducting garnets, we present a comparative study on the influence of the ionic radius of M(2+) on the 8-coordinate site and the crystal structure on the ionic transport in the solid solution Li6MLa2Ta2O12. Neutron diffraction and synchrotron diffraction in combination with AC impedance measurements are employed to understand the systematic substitution with different-sized alkaline earth cations M(2+). As may be expected, the unit-cell parameters increase linearly with increasing ionic radius from Ca(2+) over Sr(2+) to Ba(2+), accompanied by an increase in the polyhedral volumes of the dodecahedral, and tetrahedral positions and the ionic conductivities. While the TaO6 octahedral volume remain constant, the anisotropic thermal parameters of the coordinating oxygen anions suggest a high degree of rotational freedom with increasing unit-cell size. These structural parameters lead to lower activation energies because of broader Li conduction pathways and a higher flexibility in the crystal lattice, ultimately controlling the ionic conductivities in this class of materials.
受锂导电石榴石有前景的离子电导率启发，我们对Li6MLa2Ta2O12固溶体中8配位位点上M(2+)的离子半径以及晶体结构对离子传输的影响进行了比较研究。采用中子衍射和同步辐射衍射结合交流阻抗测量来理解用不同尺寸碱土金属阳离子M(2+)进行的系统取代。不出所料，随着离子半径从Ca(2+)经Sr(2+)到Ba(2+)增加，晶胞参数线性增加，同时十二面体、四面体位置的多面体体积以及离子电导率也增加。虽然TaO6八面体体积保持不变，但配位氧阴离子的各向异性热参数表明随着晶胞尺寸增加有高度的旋转自由度。这些结构参数因更宽的锂传导路径和晶格中更高的灵活性而导致更低的活化能，最终控制了这类材料中的离子电导率。
