Klenk Matthew, Lai Wei
Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, USA.
Phys Chem Chem Phys. 2015 Apr 14;17(14):8758-68. doi: 10.1039/c4cp05690f. Epub 2015 Mar 5.
To better understand the ionic conduction in lithium garnet oxides, we employed molecular dynamics simulation to investigate the local structure and dynamics of a model material Li7La3Zr2O12 and origin of its tetragonal to cubic phase transition. Our simulations were able to produce lattice parameter, neutron scattering, and conductivity data close to those gathered using experimental techniques, which allows us to study atomic-scale details of this complex material. First, it was found that lithium atoms primarily perform oscillation and "structured diffusion" dynamics in the tetragonal and cubic phase, respectively. Second, we believe that the tetragonal to cubic phase transition is an entropy-driven one that involves redistribution of lithium atoms among all tetrahedral sites. The transition is likely to initiate on the tetrahedral 8a site but needs the cooperation of neighboring octahedral 32g Li as relay atoms. Finally, it was found that a few types of lithium clusters dominate in both phases of Li7La3Zr2O12, which leads to highly correlated motion of lithium atoms. The local symmetry of these clusters dictates a "center-pass" mechanism as lithium goes through the bottleneck.
为了更好地理解锂石榴石氧化物中的离子传导，我们采用分子动力学模拟来研究模型材料Li7La3Zr2O12的局部结构和动力学及其四方相到立方相转变的起源。我们的模拟能够产生与使用实验技术收集的数据相近的晶格参数、中子散射和电导率数据，这使我们能够研究这种复杂材料的原子尺度细节。首先，发现锂原子在四方相和立方相中分别主要进行振荡和“结构化扩散”动力学。其次，我们认为四方相到立方相的转变是由熵驱动的，涉及锂原子在所有四面体位置之间的重新分布。转变可能在四面体8a位置开始，但需要相邻八面体32g锂作为中继原子的配合。最后，发现几种类型的锂簇在Li7La3Zr2O12的两个相中都占主导地位，这导致锂原子的高度相关运动。当锂通过瓶颈时，这些簇的局部对称性决定了一种“中心通过”机制。
