Fanah Selorm Joy, Ramezanipour Farshid
Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States.
Inorg Chem. 2020 Jul 20;59(14):9718-9727. doi: 10.1021/acs.inorgchem.0c00962. Epub 2020 Jun 28.
We report strategies of enhancing the ionic conductivity of triple-layered Ruddlesden-Popper oxides through design and synthesis of seven compounds belonging to the series AA'BO (A = Li, A' = La, B = Ti/Nb), investigated by neutron diffraction, impedance spectroscopy, and dielectric analyses. We demonstrate, for the first time, that lithium diffusion in triple-layered Ruddlesden-Popper oxides is a result of cooperative effect of both inter- and intrastack sites, i.e., A and A'. As shown by neutron diffraction, the structure of these materials comprises triple-layered stacks of octahedra (BO), separated by A-site cations, while A' ions reside in intrastack spaces. We first synthesized LiLaTiO and showed that its lithium-ion conductivity can be systematically enhanced by incorporation of cation deficiency in interstack sites through synthesis of LiLaTiNbO, LiLaTiNbO, and LiLaTiNbO. The latter represents the limit of cation deficiency on the A-site and has the highest conductivity among the A-site-deficient materials. We then investigated the enhancement of lithium-ion conductivity by incorporation of cation defects in intrastack A'-sites through synthesis of LiLaTiNbO and LiLaTiNbO, where the latter represents the limit of cation deficiency on the A'-site and has the best conductivity among the A'-deficient materials. Finally, we hypothesized that cooperative effect of defects in both inter- and intrastack sites should have an even higher impact on ionic conductivity. This hypothesis was confirmed by synthesis of LiLaTiNbO, which showed the highest conductivity among all materials synthesized in this work. Detailed analysis of real and imaginary components of impedance spectroscopy, as well as dielectric and loss tangent, have been conducted. This systematic study is aimed at answering a fundamental question related to materials chemistry of Ruddlesden-Popper oxides, namely, determination of the sites that contribute to ionic conductivity.
我们报告了通过设计和合成属于AA'BO系列的七种化合物（A = Li，A' = La，B = Ti/Nb）来提高三层Ruddlesden-Popper氧化物离子电导率的策略，这些化合物通过中子衍射、阻抗谱和介电分析进行了研究。我们首次证明，三层Ruddlesden-Popper氧化物中的锂扩散是层间和层内位点（即A和A'）协同作用的结果。如中子衍射所示，这些材料的结构由八面体（BO）的三层堆叠组成，由A位阳离子隔开，而A'离子位于层内空间。我们首先合成了LiLaTiO，并表明通过合成LiLaTiNbO、LiLaTiNbO和LiLaTiNbO在层间位点引入阳离子缺陷，可以系统地提高其锂离子电导率。后者代表了A位阳离子缺陷的极限，并且在A位缺陷材料中具有最高的电导率。然后，我们通过合成LiLaTiNbO和LiLaTiNbO研究了在层内A'位点引入阳离子缺陷对锂离子电导率的提高，其中后者代表了A'位阳离子缺陷的极限，并且在A'位缺陷材料中具有最佳的电导率。最后，我们假设层间和层内位点缺陷的协同作用对离子电导率应该有更高的影响。通过合成LiLaTiNbO证实了这一假设，该化合物在本工作合成的所有材料中显示出最高的电导率。我们还对阻抗谱的实部和虚部以及介电常数和损耗角正切进行了详细分析。这项系统研究旨在回答一个与Ruddlesden-Popper氧化物材料化学相关的基本问题，即确定对离子电导率有贡献的位点。
