准弹性中子散射研究锂在固体电解质La $_{2/3-x}$ Li PDMATHAAB TiO $_{3}$（$x=0.13$）单晶中扩散的微观动力学
Microscopic dynamics of lithium diffusion in single crystal of the solid-state electrolyte La$_{2/3-x}$Li$_{3x}$TiO$_{3}$ ($x=0.13$) studied by quasielastic neutron scattering
摘要：
采用准弹性中子散射（QENS）测量和基于第一性原理的分子动力学计算相结合的方法研究了固体电解质La $_{2/3-x}$ Li $_{3x}$ TiO $_{3}$（LLTO）与$x=0.13$中Li $^+$离子的动力学行为。通过使用大的$^7$富锂单晶样品，在600 K的温度（$T$）下沿三个主轴[110]，[111]和[001]清楚地观察到QENS信号。沿每个方向的QENS信号的线宽的波矢依赖性很好地解释了使用Chudley-Elliot模型通过瓶颈广场的钙钛矿晶格的A位点之间的跳跃，这也被分子动力学计算所支持。在$T=600$ K下，估计的Li $^+$（$D_{Li}$）在$ab$平面中的自扩散系数[ $D^{ab}_{Li}=(6.8\pm0.5)\times 10^{-6}$ cm $^2$ /s]略大于沿$c$轴的自扩散系数[ $D^{c}_{Li}=(4.4\pm0.3)\times 10^{-6}$ cm $^2$ /s]，表明准各向同性扩散，即Li $^+$离子的三维扩散。$D_{Li}$随$T$的降低而降低的现象可以通过热活化过程合理地解释，活化能由离子电导率测量确定。此外，Li $^+$离子的自扩散系数的估计值与基于硫化物的Li $^+$离子导体Li $_{7}$ P $_{3}$ S $_{11}$中的自扩散系数相当，尽管其离子电导率比LLTO大10倍。所获得的关于LLTO中Li $^+$扩散的微观信息阐明了如何以统一的方式理解LLTO和Li $_{7}$ P $_{3}$ S $_{11}$中的Li传导机制，并且可以提供一种增加基于氧化物的固体电解质中的Li $^+$离子电导率的方法。
英文摘要：
Quasielastic neutron scattering (QENS) measurements combined with first principles based moleculardynamics calculations were conducted to study the dynamics of Li$^+$ ions in a solid-state electrolyte La$_{2/3-x}$Li$_{3x}$TiO$_{3}$ (LLTO) with $x=0.13$. By using a large $^7$Li-enriched single crystal sample, a QENS signal was clearly observed along the three principal axes [110], [111], and [001] at a temperature ($T$) of 600 K. Wave vector dependence of the linewidth of the QENS signal along each direction was explained well using the Chudley-Elliot model for jumps between the A sites of the perovskite lattice through the bottleneck square, which was also supported by molecular dynamics calculations. At $T=600$ K, the estimated self-diffusion coefficient of Li$^+$ ($D_{Li}$) in the $ab$ plane [$D^{ab}_{Li}=(6.8\pm0.5)\times 10^{-6}$ cm$^2$/s] was slightly larger than that along the $c$ axis [$D^{c}_{Li}=(4.4\pm0.3)\times 10^{-6}$ cm$^2$/s], suggesting quasi-isotropic diffusion, that is, the three-dimensional diffusion of Li$^+$ ions. The decrease in $D_{Li}$ with decreasing $T$ was reasonably explained by a thermal activation process with the activation energy determined from ionic-conductivity measurements. Furthermore, the estimated values of the self-diffusion coefficient of Li$^+$ ions are comparable to those in the sulfide-based Li$^+$ ion conductor, Li$_{7}$P$_{3}$S$_{11}$, although its ionic conductivity is 10 times larger than that for LLTO. The obtained microscopic information on Li$^+$ diffusion in LLTO clarifies how to understand the Li conduction mechanism in LLTO and Li$_{7}$P$_{3}$S$_{11}$ in a unified manner and can provide a way to increase the Li$^+$ ionic conductivity in oxide-based solid electrolytes.
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