cm502133c_si_003.mpg (4.51 MB)
Local Structure and Dynamics of Lithium Garnet Ionic Conductors: A Model Material Li5La3Ta2O12
media
posted on 2014-10-14, 00:00 authored by Yuxing Wang, Matthew Klenk, Katharine Page, Wei LaiIn
this article, we combined two complementary structure/dynamics
probes, i.e., total-scattering/reverse Monte Carlo (RMC) modeling
and classical molecular dynamics (MD), in order to understand local
lithium structure and dynamics in a model disordered garnet oxide
Li5La3Ta2O12. By examining
the configurations from RMC and trajectories from MD, we individually
and statistically analyzed the lithium distribution and dynamics within
tetrahedral (Td) cages, octahedral (Oh) cages, and triangular bottlenecks.
We found that lithium atoms within either Td or Oh cages prefer to
stay at the off-center positions and close to one of the triangular
bottlenecks. This is likely caused by the uneven Li–Li interaction
in the form of lithium clusters, and such geometrical frustration
leads to the local structure instability and fast ionic conduction.
Both RMC and MD studies support that the lithium conduction path goes
through the triangular bottleneck in a 3D continuous network of Td/Oh
cages, without a direct Oh to Oh jump. However, the conduction mechanism
should not be generalized, as it is greatly influenced by the local
environment or temperature. Broadly speaking, lithium atoms hop through
the bottleneck from an edge-passing mechanism at low temperatures
to a center-passing mechanism at higher temperatures.