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Abstract
Although
the fascinatingly rich crystal chemistry of honeycomb layered oxides has been
accredited as the propelling force behind their remarkable electrochemistry,
the atomistic mechanisms surrounding their operations remain unexplored. Thus,
herein, we present an extensive molecular dynamics study performed
systematically using a refined set of inter-atomic potential parameters of A2Ni2TeO6
(where A = Li, Na, and K). We
demonstrate the effectiveness of the Vashishta-Rahman form of the interatomic
potential in reproducing various structural and transport properties of this
promising class of materials and predict an exponential increase in cationic
diffusion with larger interlayer distances. The simulations further demonstrate
the correlation between broadened inter-layer (inter-slab) distances associated
with the larger ionic radii of K and Na compared to Li and the enhanced
cationic conduction exhibited in K2Ni2TeO6 and
Na2Ni2TeO6 relative to Li2Ni2TeO6.
Whence, our findings connect lower
potential energy barriers, favourable cationic paths and wider bottleneck size
along the cationic diffusion channel within frameworks (comprised of larger
mobile cations) to the improved cationic diffusion experimentally observed in
honeycomb layered oxides. Furthermore, we explicitly study the role of
inter-layer distance and cationic size in cationic diffusion. Our theoretical
studies reveal the dominance of inter-layer distance over cationic size, a
crucial insight into the further performance enhancement of honeycomb layered
oxides.
