arXiv subjects

Tomohiro Saito

Publications and source records attributed to Tomohiro Saito.

6 recordsLinked to original sources

arXiv2024

Exploring $\rm Mg^{2+}$ and $\rm Ca^{2+}$ Conductors Via Solid-State Metathesis Reactions

The scarcity of viable electrode and electrolyte materials vastly hinders the advancement of magnesium and calcium batteries. This study utilises solid-state metathetical reactions involving chalcogen- and pnictogen-based honeycomb layered oxides with alkaline-earth halides/nitrates to synthesise $\rm Mg^{2+}$- and $\rm Ca^{2+}$-based materials previously achievable only under high-temperature/high-pressure conditions, as well as new metastable materials with unique crystal versatility. Particularly, we employ metathetical reactions involving $\rm Li_4MgTeO_6$, $\rm Na_2Mg_2TeO_6$, and $\rm Na_4MgTeO_6$ with $\rm MgCl_2$/$\rm MgSO_4$/$\rm Mg(NO_3)_2$.$\rm 6H_2O$ or $\rm Ca(NO_3)_2$.$\rm 4H_2O$ / $\rm CaCl_2$.$\rm 2H_2O$ at temperatures not exceeding 500 $^\circ$C to produce $\rm Mg_3TeO_6$ polymorphs, ilmenite-type $\rm CaMg_2TeO_6$/$\rm Mg_2CaTeO_6$, and double perovskite-type $\rm Ca_2MgTeO_6$. Thus, we demonstrate that these materials, conventionally requiring gigascale pressures or high temperatures (>1000$^\circ$C) for their proper synthesis, are now readily accessible at ambient pressure and considerably lower temperatures. Meanwhile, despite sub-optimal pellet densities, the synthesised ilmenite-type \magenta {$\rm Mg_3TeO_6$ (high-pressure polymorph)} and double perovskite-type ${\rm Ca}_2M{\rm TeO_6}$ ($M = \rm Mg, Ca, Zn$) materials exhibit remarkable bulk ionic conductivity at room temperature, marking them as promising compositional spaces for exploring novel $\rm Mg^{2+}$ and $\rm Ca^{2+}$ conductors. Furthermore, this study extends the applicability of metathetical reactions to attain Mg- or Ca-based antimonates, ruthenates, titanates, phosphates, and silicates, thus opening avenues to novel high-entropy multifunctional nanomaterial platforms with utility in energy storage and beyond.

cond-mat.mtrl-sci↗

arXiv2023

Honeycomb Layered Frameworks with Metallophilic Bilayers

This Review highlights the exciting advancements in the science of honeycomb layered frameworks with metallophilic bilayers that have recently garnered attention particularly due to reports of anomalous fractional valency states of silver cations sandwiched between transition metal slabs of other cations. First, the latest tactics and techniques including but not limited to X-ray absorption spectroscopy (XAS) and high-resolution transmission electron microscopy (HRTEM) particularly necessary for characterising recent honeycomb layered frameworks with metallophilic bilayers are described, with emphasis on silver-based oxides. Second, new strategies and concepts related to topochemically- or temperature-induced cationic-deficient phases expanding the compositional space of honeycomb layered frameworks focused on cationic bilayer architectures are also accentuated. Third, the latest condensed matter theoretic advances towards a full, atomistic description of the bilayered structure in such frameworks are detailed, especially related to critical phenomena at the cusp of the monolayer-bilayer phase transition. This entails, in part, describing honeycomb layered frameworks as optimised lattices within the congruent sphere packing problem, equivalent to a particular two-dimensional (2D) conformal field theory. Altogether, it is hoped that this Review will give the reader a panoramic view of the honeycomb layered frameworks with important applications within the emerging field of quantum matter, potentially redefining their frontier. Thus, the scope of this Review is expected to be worthwhile for recent graduates and emerging experts alike not only in the materials science and chemistry community but also in other diverse fields of interest.

cond-mat.mtrl-sci↗

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

Topological Defects and Unique Stacking Disorders in Honeycomb Layered Oxide $\rm K_2Ni_2TeO_6$ Nanomaterials: Implications for Rechargeable Batteries

Endowed with a multitude of exquisite properties such as rich electrochemistry, superb topology and eccentric electromagnetic phenomena, honeycomb layered oxides have risen to the top echelons of science with applications in diverse fields ranging from condensed matter physics, solid-state chemistry, materials science, solid-state ionics to electrochemistry. However, these oxides are vastly underutilised as their underlying atomistic mechanisms remain unexplored. Therefore, in this study, atomic-resolution imaging on pristine $\rm K_2Ni_2TeO_6$ along multiple zone axes was conducted using spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) to reveal hitherto unreported nanoscale topological defects and curvature which can be associated with various phase transitions. Furthermore, we discover the coexistence of a stacking variant with P3-type sequence alongside the well-reported P2-type stacking sequence in such honeycomb layered oxides. Our findings have the potential to inspire further experimental and theoretical studies into the role of stacking and topology in the functionality of honeycomb layered oxides, for instance, as high-performance electrode materials for rechargeable batteries.

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↗