An idealised approach of geometry and topology to the diffusion of cations in honeycomb layered oxide frameworks

Godwill Mbiti Kanyolo,Titus Masese

doi:10.1038/s41598-020-70019-9

Abstract

Honeycomb layered oxides are a novel class of nanostructured materials comprising alkali or coinage metal atoms intercalated into transition metal slabs. The intricate honeycomb architecture and layered framework endows this family of oxides with a tessellation of features such as exquisite electrochemistry, unique topology and fascinating electromagnetic phenomena. Despite having innumerable functionalities, these materials remain highly underutilised as their underlying atomistic mechanisms are vastly unexplored. Therefore, in a bid to provide a more in-depth perspective, we propose an idealised diffusion model of the charged alkali cations (such as lithium, sodium or potassium) in the two-dimensional (2D) honeycomb layers within the multi-layered crystal of honeycomb layered oxide frameworks. This model not only explains the correlation between the excitation of cationic vacancies (by applied electromagnetic fields) and the Gaussian curvature deformation of the 2D surface, but also takes into consideration, the quantum properties of the cations and their inter-layer mixing through quantum tunnelling. Through this work, we offer a novel theoretical framework for the study of multi-layered materials with 2D cationic diffusion currents, as well as providing pedagogical insights into the role of topological phase transitions in these materials in relation to Brownian motion and quantum geometry.

Highlights

Honeycomb layered oxides are a novel class of nanostructured materials comprising alkali or coinage metal atoms intercalated into transition metal slabs
There is a correlation between the stacking structure and the resulting electrochemical performance of the honeycomb layered oxides that can be traced to the differing sizes of the A+ cations
We focus on the prismatic subclass of honeycomb layered oxides that generally adopt A+2 L22+D6+O6 compositions, where A = K, Li or Na is an alkali cation owing to their exemplary electrochemical and physical properties[1,5,6,7,8,11,12,13,14,15,16,19,20,28,39]

Summary

Introduction

Honeycomb layered oxides are a novel class of nanostructured materials comprising alkali or coinage metal atoms intercalated into transition metal slabs. The weaker inter-layer bonds in prismatic layered (P-type) structures create more open voids within the transition metal layers allowing for facile two-dimensional diffusion of alkali atoms within the slabs[41] This gives rise to the high ionic mobility and exceptional electrochemical properties innate in honeycomb layered oxides. We focus on the prismatic subclass of honeycomb layered oxides that generally adopt A+2 L22+D6+O6 (or equivalently A+2/3L22/+3D16/+3O2 ) compositions, where A = K, Li or Na is an alkali cation (potassium, lithium or sodium) owing to their exemplary electrochemical and physical properties[1,5,6,7,8,11,12,13,14,15,16,19,20,28,39] We explore their cationic diffusion by envisioning an idealised model of multi-layered oxides in an attempt to gain an effective description of the diffusion mechanics along the honeycomb layers using concepts of 2D curvature and topology.

Results

Discussion

Conclusion