Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
66,719
result(s) for
"Metal compounds"
Sort by:
Extra storage capacity in transition metal oxide lithium-ion batteries revealed by in situ magnetometry
In lithium-ion batteries (LIBs), many promising electrodes that are based on transition metal oxides exhibit anomalously high storage capacities beyond their theoretical values. Although this phenomenon has been widely reported, the underlying physicochemical mechanism in such materials remains elusive and is still a matter of debate. In this work, we use in situ magnetometry to demonstrate the existence of strong surface capacitance on metal nanoparticles, and to show that a large number of spin-polarized electrons can be stored in the already-reduced metallic nanoparticles (that are formed during discharge at low potentials in transition metal oxide LIBs), which is consistent with a space charge mechanism. Through quantification of the surface capacitance by the variation in magnetism, we further show that this charge capacity of the surface is the dominant source of the extra capacity in the Fe
3
O
4
/Li model system, and that it also exists in CoO, NiO, FeF
2
and Fe
2
N systems. The space charge mechanism revealed by in situ magnetometry can therefore be generalized to a broad range of transition metal compounds for which a large electron density of states is accessible, and provides pivotal guidance for creating advanced energy storage systems.
Although some transition metal oxide-based electrodes exhibit high storage capacities beyond theoretical values, the underlying physicochemical mechanism remains elusive. Surface capacitance on metal nanoparticles involving spin-polarized electrons is now shown to be consistent with a space charge mechanism.
Journal Article
Twofold symmetry of c-axis resistivity in topological kagome superconductor CsV3Sb5 with in-plane rotating magnetic field
In transition metal compounds, due to the interplay of charge, spin, lattice and orbital degrees of freedom, many intertwined orders exist with close energies. One of the commonly observed states is the so-called nematic electron state, which breaks the in-plane rotational symmetry. This nematic state appears in cuprates, iron-based superconductor, etc. Nematicity may coexist, affect, cooperate or compete with other orders. Here we show the anisotropic in-plane electronic state and superconductivity in a recently discovered kagome metal CsV
3
Sb
5
by measuring
c
-axis resistivity with the in-plane rotation of magnetic field. We observe a twofold symmetry of superconductivity in the superconducting state and a unique in-plane nematic electronic state in normal state when rotating the in-plane magnetic field. Interestingly these two orders are orthogonal to each other in terms of the field direction of the minimum resistivity. Our results shed new light in understanding non-trivial physical properties of CsV
3
Sb
5
.
The recently discovered class of kagome metals AV
3
Sb
5
, where A stands for K, Rb, Cs, has been shown to host a variety of exotic phases. Here, the authors report the two-fold rotational symmetry of superconductivity and signatures of an in-plane nematic electronic state in CsV
3
Sb
5
under in-plane magnetic field.
Journal Article
Half- and quarter-metals in rhombohedral trilayer graphene
Ferromagnetism is most common in transition metal compounds where electrons occupy highly localized
d
orbitals. However, ferromagnetic order may also arise in low-density two-dimensional electron systems
1
–
5
. Here we show that gate-tuned van Hove singularities in rhombohedral trilayer graphene
6
drive spontaneous ferromagnetic polarization of the electron system into one or more spin and valley flavours. Using capacitance and transport measurements, we observe a cascade of transitions tuned to the density and electronic displacement field between phases in which quantum oscillations have fourfold, twofold or onefold degeneracy, associated with a spin- and valley-degenerate normal metal, spin-polarized ‘half-metal’, and spin- and valley-polarized ‘quarter-metal’, respectively. For electron doping, the salient features of the data are well captured by a phenomenological Stoner model
7
that includes valley-anisotropic interactions. For hole filling, we observe a richer phase diagram featuring a delicate interplay of broken symmetries and transitions in the Fermi surface topology. Finally, we introduce a moiré superlattice using a rotationally aligned hexagonal boron nitride substrate
5
,
8
. Remarkably, we find that the isospin order is only weakly perturbed, with the moiré potential catalysing the formation of topologically nontrivial gapped states whenever itinerant half- or quarter-metal states occur at half- or quarter-superlattice band filling. Our results show that rhombohedral graphene is an ideal platform for well-controlled tests of many-body theory, and reveal magnetism in moiré materials
4
,
5
,
9
,
10
to be fundamentally itinerant in nature.
A study shows that rhombohedral graphene is an ideal platform for well-controlled tests of many-body theory and reveals that magnetism in moiré materials is fundamentally itinerant in nature.
Journal Article
A library of atomically thin metal chalcogenides
Investigations of two-dimensional transition-metal chalcogenides (TMCs) have recently revealed interesting physical phenomena, including the quantum spin Hall effect
1
,
2
, valley polarization
3
,
4
and two-dimensional superconductivity
5
, suggesting potential applications for functional devices
6
–
10
. However, of the numerous compounds available, only a handful, such as Mo- and W-based TMCs, have been synthesized, typically via sulfurization
11
–
15
, selenization
16
,
17
and tellurization
18
of metals and metal compounds. Many TMCs are difficult to produce because of the high melting points of their metal and metal oxide precursors. Molten-salt-assisted methods have been used to produce ceramic powders at relatively low temperature
19
and this approach
20
was recently employed to facilitate the growth of monolayer WS
2
and WSe
2
. Here we demonstrate that molten-salt-assisted chemical vapour deposition can be broadly applied for the synthesis of a wide variety of two-dimensional (atomically thin) TMCs. We synthesized 47 compounds, including 32 binary compounds (based on the transition metals Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re, Pt, Pd and Fe), 13 alloys (including 11 ternary, one quaternary and one quinary), and two heterostructured compounds. We elaborate how the salt decreases the melting point of the reactants and facilitates the formation of intermediate products, increasing the overall reaction rate. Most of the synthesized materials in our library are useful, as supported by evidence of superconductivity in our monolayer NbSe
2
and MoTe
2
samples
21
,
22
and of high mobilities in MoS
2
and ReS
2
. Although the quality of some of the materials still requires development, our work opens up opportunities for studying the properties and potential application of a wide variety of two-dimensional TMCs.
Molten-salt-assisted chemical vapour deposition is used to synthesize a wide variety of two-dimensional transition-metal chalcogenides.
Journal Article
A Review on Engineering Transition Metal Compound Catalysts to Accelerate the Redox Kinetics of Sulfur Cathodes for Lithium–Sulfur Batteries
HighlightsThe representatively engineering strategies of cations/anions doping, bimetallic/bi-anionic transition metal compounds and heterostructure composites catalysts for lithium sulfur batteries are comprehensively reviewed.The promoted mechanism of catalytic performance by regulating electronic structure is focused on, including energy band, electron filling, d/p-band center, valence state.The superiority of the modified transition metal compounds is comprehensively summarized.Engineering transition metal compounds (TMCs) catalysts with excellent adsorption-catalytic ability has been one of the most effective strategies to accelerate the redox kinetics of sulfur cathodes. Herein, this review focuses on engineering TMCs catalysts by cation doping/anion doping/dual doping, bimetallic/bi-anionic TMCs, and TMCs-based heterostructure composites. It is obvious that introducing cations/anions to TMCs or constructing heterostructure can boost adsorption-catalytic capacity by regulating the electronic structure including energy band, d/p-band center, electron filling, and valence state. Moreover, the electronic structure of doped/dual-ionic TMCs are adjusted by inducing ions with different electronegativity, electron filling, and ion radius, resulting in electron redistribution, bonds reconstruction, induced vacancies due to the electronic interaction and changed crystal structure such as lattice spacing and lattice distortion. Different from the aforementioned two strategies, heterostructures are constructed by two types of TMCs with different Fermi energy levels, which causes built-in electric field and electrons transfer through the interface, and induces electron redistribution and arranged local atoms to regulate the electronic structure. Additionally, the lacking studies of the three strategies to comprehensively regulate electronic structure for improving catalytic performance are pointed out. It is believed that this review can guide the design of advanced TMCs catalysts for boosting redox of lithium sulfur batteries.
Journal Article
Versatile synthesis of metal-compound based mesoporous Janus nanoparticles
The construction of mesoporous Janus nanoparticles (mJNPs) with controllable components is of great significance for the development of sophisticated nanomaterials with synergistically enhanced functionalities and applications. However, the compositions of reported mJNPs are mainly the functionally inert SiO
2
and polymers. The universal synthesis of metal-compound based mJNPs with abundant functionalities is urgently desired, but remains a substantial challenge. Herein, we present a hydrophilicity mediated interfacial selective assembly strategy for the versatile synthesis of metal-compound based mJNPs. Starting from the developed silica-based mJNPs with anisotropic dual-surface of hydrophilic SiO
2
and hydrophobic organosilica, metal precursor can selectively deposit onto the hydrophilic SiO
2
subunit to form the metal-compound based mJNPs. This method shows good universality and can be used for the synthesis of more than 20 kinds of metal-compound based mJNPs, including alkali-earth metal compounds, transition metal compounds, rare-earth metal compounds etc. Besides, the composition of the metal-compound subunit can be well tuned from single to multiple metal elements, even high-entropy complexes. We believe that the synthesis method and obtained new members of mJNPs provide a very broad platform for the construction and application of mJNPs with rational designed functions and structures.
Mesoporous Janus nanoparticles (mJNPs) have attracted a lot of attention due to their unique morphology. Here, the authors demonstrate a hydrophilicity mediated interfacial selective assembly strategy for the versatile synthesis of metal compound based mJNPs.
Journal Article
Boosting Lean Electrolyte Lithium–Sulfur Battery Performance with Transition Metals: A Comprehensive Review
HighlightsThis review systematically analyzes the effect of the electrolyte-to-sulfur ratios on battery energy density and the challenges for sulfur reduction reactions under lean electrolyte conditions.The strengths and limitations of different transition metal compounds are systematically presented and discussed from a fundamental perspective.Three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li–S battery performance.Lithium–sulfur (Li–S) batteries have received widespread attention, and lean electrolyte Li–S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg−1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li–S battery performance. Finally, an outlook is provided to guide future research on high energy density Li–S batteries.
Journal Article
Concept and realization of Kitaev quantum spin liquids
The Kitaev model is an exactly solvable S = 1/2 spin model on a 2D honeycomb lattice, in which the spins fractionalize into Majorana fermions and form a topological quantum spin liquid (QSL) in the ground state. Several complex iridium oxides, as well as α-RuCl3, are magnetic insulators with a honeycomb structure, and it was noticed that they accommodate essential ingredients of the Kitaev model owing to the interplay of electron correlation and spin–orbit coupling. This has led to a race to realize the Kitaev QSL and detect signatures of Majorana fermions. We summarize the theoretical background of the Kitaev QSL ground state and its realization using spin–orbital entangled Jeff = 1/2 moments. We provide an overview of candidate materials and their electronic and magnetic properties, including Na2IrO3, α-Li2IrO3, β-Li2IrO3, γ-Li2IrO3, α-RuCl3 and H3LiIr2O6. Finally, we discuss experiments showing that H3LiIr2O6 and α-RuCl3 in an applied magnetic field exhibit signatures of the QSL state and that α-RuCl3 has unusual magnetic excitations and thermal transport properties consistent with spin fractionalization.The Kitaev quantum spin liquid is an exotic phase of matter exhibiting long-range entanglement and emergent Majorana fermions. This Review summarizes the concept and recent progress in realizing Kitaev model physics in transition metal compounds.
Journal Article
Recent Developments of Transition Metal Compounds-Carbon Hybrid Electrodes for High Energy/Power Supercapacitors
HighlightsThe development of transition metal compounds-carbon hybrid electrodes for high energy/power supercapacitors is summarized.Effects of the conductive carbon skeleton, interfacial engineering, and electronic structure for transition metal compounds-carbon hybrid are discussed.Some perspectives and issues in the future are provided.Due to their rapid power delivery, fast charging, and long cycle life, supercapacitors have become an important energy storage technology recently. However, to meet the continuously increasing demands in the fields of portable electronics, transportation, and future robotic technologies, supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged. Transition metal compounds (TMCs) possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors. However, the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process, which greatly impede their large-scale applications. Most recently, the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges. Herein, we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies, including conductive carbon skeleton, interface engineering, and electronic structure. Furthermore, the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.
Journal Article