Honeycomb-Layered Oxides With Silver Atom Bilayers and Emergence of Non-Abelian SU(2) Interactions

Abstract

Honeycomb-layered oxides with monovalent or divalent, monolayered cationic lattices generally exhibit myriad crystalline features encompassing rich electrochemistry, geometries, and disorders, which particularly places them as attractive material candidates for next-generation energy storage applications. Herein, global honeycomb-layered oxide compositions, Ag₂ M₂ TeO₆ ( $M=\mathrm{Ni},\mathrm{Mg},\mathrm{etc}$ .) exhibiting $\mathrm{Ag}$ atom bilayers with sub-valent states within Ag-rich crystalline domains of Ag₆ M₂ TeO₆ and $\mathrm{Ag}$ -deficient domains of ${\mathrm{Ag}}_{2-x}{\mathrm{Ni}}_2{\mathrm{TeO}}_6$ ( $0<x<2$ ). The $\mathrm{Ag}$ -rich material characterized by aberration-corrected transmission electron microscopy reveals local atomic structural disorders characterized by aperiodic stacking and incoherency in the bilayer arrangement of $\mathrm{Ag}$ atoms. Meanwhile, the global material not only displays high ionic conductivity but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the $\mathrm{Ag}$ -rich domains, the bilayered structure, argentophilic interactions therein and the expected $\mathrm{Ag}$ sub-valent states ( $1/2+,2/3+$ , etc.) are theoretically understood via spontaneous symmetry breaking of SU(2)× U(1) gauge symmetry interactions amongst 3 degenerate mass-less chiral fermion states, justified by electron occupancy of silver $4d_{z^2}$ and 5s orbitals on a bifurcated honeycomb lattice. This implies that bilayered frameworks have research applications that go beyond the confines of energy storage.

Keywords: aberration-corrected transmission electron microscopy; argentophilic interactions; honeycomb-layered oxides; silver bilayers; sub-valent degenerate states.