arXiv subjects

Josef Rizell

Publications and source records attributed to Josef Rizell.

5 recordsLinked to original sources

arXiv2022

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

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, we report global honeycomb layered oxide compositions, ${\rm Ag_2}M_2{\rm TeO_6}$ ($M = \rm Ni, Mg, \textit{etc}.$) exhibiting $\rm Ag$ atom bilayers with sub-valent states within Ag-rich crystalline domains of ${\rm Ag_6}M_2{\rm TeO_6}$ and $\rm Ag$-deficient domains of ${\rm Ag}_{2 - x}\rm Ni_2TeO_6$ ($0 < x < 2$). The $\rm Ag$-rich material characterised by aberration-corrected transmission electron microscopy reveals local atomic structural disorders characterised by aperiodic stacking and incoherency in the bilayer arrangement of $\rm Ag$ atoms. Meanwhile, the global material not only displays high ionic conductivity, but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the $\rm Ag$-rich domains, the bilayered structure, argentophilic interactions therein and the expected $\rm Ag$ sub-valent states ($1/2+, 2/3+, \textit{etc}.$) are theoretically understood via spontaneous symmetry breaking of SU($2$)$\times$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.

cond-mat.mtrl-sci↗

arXiv2021

Unveiling Structural Disorders in Honeycomb Layered Oxide: $\rm Na_2Ni_2TeO_6$

Honeycomb layered oxides have garnered tremendous research interest in a wide swath of disciplines owing not only to the myriad physicochemical properties they exhibit, but also their rich crystal structural versatility. Herein, a comprehensive crystallographic study of a sodium-based $\rm Na_2Ni_2TeO_6$ honeycomb layered oxide has been performed using atomic-resolution transmission electron microscopy, elucidating a plethora of atomic arrangement (stacking) disorders in the pristine material. Stacking disorders in the arrangement of honeycomb metal slab layers (stacking faults) occur predominantly perpendicular to the slabs with long-range coherence length and enlisting edge dislocations in some domains. Moreover, the periodic arrangement of the distribution of alkali atoms is altered by the occurrence of stacking faults. The multitude of disorders innate in $\rm Na_2Ni_2TeO_6$ envisage broad implications in the functionalities of related honeycomb layered oxide materials and hold promise in bolstering renewed interest in their material science.

cond-mat.mtrl-sci↗

arXiv2021

Mixed Alkali-Ion Transport and Storage in Atomic-Disordered Honeycomb Layered $\rm NaKNi_2TeO_6$

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms ($\rm Na$ and $\rm K$) to produce a mixed alkali honeycomb layered oxide material, namely, $\rm NaKNi_2TeO_6$. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of $\rm Na$ and $\rm K$ atoms. We also investigate the possibility of mixed electrochemical transport and storage of $\rm Na$ and $\rm K$ ions in $\rm NaKNi_2TeO_6$. In particular, we report an average discharge cell voltage of about $4\, \rm V$ and a specific capacity of around $80\, \rm mAh\, g^{-1}$ at low specific currents (i.e., $< 10\, \rm mA\, g^{-1}$) when a $\rm NaKNi_2TeO_6$-based positive electrode is combined with a room-temperature $\rm NaK$ liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for dendrite-free electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials.

cond-mat.mtrl-sci↗

arXiv2020

Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant Insights

The advent of nanotechnology has hurtled the discovery and development of nanostructured materials with stellar chemical and physical functionalities in a bid to address issues in energy, environment, telecommunications and healthcare. In this quest, a class of two-dimensional layered materials consisting of alkali or coinage metal atoms sandwiched between slabs exclusively made of transition metal and chalcogen (or pnictogen) atoms arranged in a honeycomb fashion have emerged as materials exhibiting fascinatingly rich crystal chemistry, high-voltage electrochemistry, fast cation diffusion besides playing host to varied exotic electromagnetic and topological phenomena. Currently, with a niche application in energy storage as high-voltage materials, this class of honeycomb layered oxides serves as ideal pedagogical exemplars of the innumerable capabilities of nanomaterials drawing immense interest in multiple fields ranging from materials science, solid-state chemistry, electrochemistry and condensed matter physics. In this review, we delineate the relevant chemistry and physics of honeycomb layered oxides, and discuss their functionalities for tunable electrochemistry, superfast ionic conduction, electromagnetism and topology. Moreover, we elucidate the unexplored albeit vastly promising crystal chemistry space whilst outlining effective ways to identify regions within this compositional space, particularly where interesting electromagnetic and topological properties could be lurking within the aforementioned alkali and coinage-metal honeycomb layered oxide structures. We conclude by pointing towards possible future research directions, particularly the prospective realisation of Kitaev-Heisenberg-Dzyaloshinskii-Moriya interactions with single crystals and Floquet theory in closely-related honeycomb layered oxide materials.

cond-mat.mtrl-sci↗

arXiv2020

High-Voltage Honeycomb Layered Oxide Positive Electrodes for Rechargeable Sodium Batteries

Natural abundance, impressive chemical characteristics and economic feasibility have rekindled the appeal for rechargeable sodium (Na) batteries as a practical solution for the growing energy demand, environmental sustainability and energy independence. However, the scarcity of viable positive electrode materials remains a huge impediment to the actualization of this technology. In this paper, we explore honeycomb layered oxides adopting the composition Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ ($x = 0, 0.25$ and $0.50$) as feasible positive electrode (cathode) materials for rechargeable sodium batteries at both room- and elevated temperatures using ionic liquids. Through standard galvanostatic assessments and analyses we demonstrate that substitution of nickel with cobalt in Na$_2$Ni$_2$TeO$_6$ leads to an increase in the discharge voltage to nearly $4$ V (versus Na$^+$ / Na) for the Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ family of honeycomb layered oxide materials, which surpasses the attained average voltages for most layered oxide positive electrode materials that facilitate Na-ion desertion. We also verify the increased kinetics within the Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ honeycomb layered oxides during operations at elevated temperatures which lead to an increase in reversible capacity of the rechargeable Na battery. This study underpins the doping of congener transition metal atoms to the honeycomb structure of Na$_2$Ni$_2$TeO$_6$ in addition to elevated-temperature operation as a judicious route to enhance the electrochemical performance of analogous layered oxides.

cond-mat.mtrl-sci↗