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, Ag 2 M 2 TeO 6 (M = Ni, Mg, etc.) exhibiting Ag atom bilayers with sub-valent states within Ag-rich crystalline domains of Ag 6 M 2 TeO 6 and Ag-deficient domains of Ag 2−x Ni 2 TeO 6 (0 < x < 2). The 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 Ag atoms. Meanwhile, the global material not only displays high ionic conductivity but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the Ag-rich domains, the bilayered structure, argentophilic interactions therein and the expected 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.

Antiferromagnetic ordering and signatures of enhanced spin-frustration in honeycomb-layered tellurates with Ag bilayers

“…It has been recently theorized that a weak attractive interaction between Ag atoms constituting argentophilicity resulting from pseudo-spin symmetry is responsible for the unconventional formation and stability of the Ag bilayers. 27,28…”

“…Further details on the sample synthesis are described elsewhere. 28 Magnetic properties of the samples are characterized using a Quantum Design Magnetic Property Measurement System with a temperature-range of 2-300 K and a magnetic field-range of AE 70 kOe. The crystal structures in ESI † are visualized by the VESTA program.…”

“…From temperature and field dependent magnetization measurements, we observe antiferromagnetic ordering and signatures of spin-frustration in the vicinity of the antiferromagnetic phase transition which might result from enhanced 2D magnetic ordering due to the screening of the interslab exchange coupling by the Ag bilayers. 27 In addition, the formation of Ag-bilayers recently discovered 28 further extends the interslab distance relative to its monolayered counterpart. It has been recently theorized that a weak attractive interaction between Ag atoms constituting argentophilicity resulting from pseudo-spin symmetry is responsible for the unconventional formation and stability of the Ag bilayers.…”

“…It has been recently theorized that a weak attractive interaction between Ag atoms constituting argentophilicity resulting from pseudo-spin symmetry is responsible for the unconventional formation and stability of the Ag bilayers. 27,28 In Fig. 2(a)-(c), we plot the magnetic susceptibility (w) versus temperature (T) curves at the magnetic field (H) of 100 Oe for polycrystalline powders of global composition Ag 2 M 2 TeO 6 with M = Co, Co 0.5 Ni 0.5 , and Ni, respectively.…”

“…Unlike other tellurates, in Ag 2Àx M 2 TeO 6 (0 o x r 2) (M = Co, Co 0.5 Ni 0.5 , and Ni), a straight dumbbell-like coordination between the d-orbitals of Ag + and the 2p-orbitals of O 2À along the interslabs enhances the interslab distance between the (Te, M)-O layers 27. In addition, the formation of Ag-bilayers recently discovered28 further extends the interslab distance relative to its monolayered counterpart. It has been recently theorized that a weak attractive interaction between Ag atoms constituting argentophilicity…”