Academic literature on the topic 'Transition Metal Oxides (TMOs) - Novel Crystal Structure'

Magnetic anisotropy (MA) is one of the most important material properties for modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e., magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry. Extrinsic control over the MA is usually achieved by introducing shape anisotropy or exchange bias from another magnetically ordered material. Here we demonstrate a pathway to manipulate MA of 3d transition-metal oxides (TMOs) by digitally inserting nonmagnetic 5d TMOs with pronounced spin–orbit coupling (SOC). High-quality superlattices comprising ferromagnetic La2/3Sr1/3MnO3 (LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control of thickness at the atomic scale. Magnetic easy-axis reorientation is observed by controlling the dimensionality of SIO, mediated through the emergence of a novel spin–orbit state within the nominally paramagnetic SIO.

In this era of transitioning from conventional sources of energy to non-conventional, sodium-ion battery research has been burgeoning as an indigenous solution to energy storage applications, considering the sustainability, cost effectiveness, high availability and a familiar redox chemistry 1. P2-type Na2/3Ni1/3Mn2/3O2 is one of the preeminent cathode for sodium-ion batteries because of their environmental friendliness, open framework, superior specific capacity, higher operating voltage and air-moisture stability. However, rapid capacity decay on charging it to a higher voltage because of P2 to O2 phase transition and a large volume change leading to exfoliation of the layers have impeded the practicability of this as an electrode material for Na-ion battery 2,3,4. Here in this work, we report the preparation of hexagonal nanocrystals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, which is titanium doped in pristine Na2/3Ni1/3Mn2/3O2 via a novel and quick microwave synthesis technique. This provides sharp and clear facets that allows accelerated sodium-ion migration within the crystal during extraction and insertion of Na-ions, making this material a highly efficient cathode. Unlike conventional heating, which requires around 12-20 hours of synthesis time and high energy consumption, microwave radiation induces rapid solid-state reaction that heats the material on molecular level leading to uniform heating, thus retaining the nanocrystallinity of the structure 5. The distinctive hierarchical nanostructure having large surface area could efficiently facilitate the transportation of Na+ ions, fast utilization of active materials, overcome the effect of internal strain generated inside and reduces the pulverization of active materials, thereby restraining the P2 to O2 phase transition at higher voltage 6. Aiding from the combined effect of titanium doping at manganese site and designing hierarchical nanocrystrals of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2, we obtained a rate capability of 145 mAh g-1 at 0.1 C and a prolonged cycling life (87.3% capacity retention after 500 cycles at 1C) within a voltage range of 2.5 – 4.2 V, restraining the P2 to O2 type phase transition at higher potential. The combined analysis of X-ray diffraction, scanning electron microscopy and transmission electron microscopy along with density functional theory (DFT) calculations demonstrated the optimization of the structure and the physical properties of pristine Na2/3Ni1/3Mn2/3O2 and Ti doped structure along with their Bader charge analysis and electronic properties. Further the mechanical integrity of the nano Na2/3Ni1/3Mn1/2Ti1/6O2 and micro Na2/3Ni1/3Mn1/2Ti1/6O2 were analyzed through micro-compression test of the as prepared pellets. The underlying mechanism for the suppression of phase transition in Na2/3Ni1/3Mn1/2Ti1/6O2 was elucidated by ex-situ X-ray diffraction (XRD) and ex-situ Transmission electron microscopy (TEM). The electrochemical kinetics regarding Na+ diffusion coefficient was further studied through galvanostatic intermittent titration technique (GITT). An analytical model was established to probe deeper into the reason for exfoliation and thus, support our hypothesis. In addition, a sodium-ion full cell was constructed by pairing the as-prepared P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 with a hard carbon anode. This modification of P2-type Na2/3Ni1/3Mn1/2Ti1/6O2 nanocrystallites with comprehensive electrochemical performance can be a path breaking, highly efficient cathode material for large-scale energy storage applications. References: Larcher, D. & Tarascon, J. M. Towards greener and more sustainable batteries for electrical energy storage. Chem. 7, 19–29 (2015). Lu, Z. & Dahn, J. R. In Situ X-Ray Diffraction Study of P2-Na2/3Ni1/3Mn2/3O2. Electrochem. Soc. 148, A1225 (2001) Delmas, C., Fouassier, C. & Hagenmuller, P. Structural classification and properties of the layered oxides. B+C. 99, 81 – 85 (1980) Stansby, J. H., Sharma, N. & Goonetilleke, D. Probing the charged state of layered positive electrodes in sodium-ion batteries: Reaction pathways, stability and opportunities. J. Mater. Chem. A 8, 24833–24867 (2020) Muraligantha T, Murugan A. V, Manthiram A. Facile synthesis of carbon-decorated single-crystalline Fe3O4 nanowires and their application as high performance anode in lithium ion batteries. Commun. 7360 – 7362 (2009) Sun Y, Liu N, Cui Y. Promises and challenges of nanomaterials for lithium-based rechargeable batteries. Nature Energy. 1, 16071 (2016)

Herein, a versatile sol-gel reaction produces new electrode materials consisting of tightly integrated molybdenum oxide and carbon derived from chemically incorporated dopamine molecules, and the materials show enhanced electrochemical activity in nonaqueous Li-ion and aqueous Zn-ion energy storage systems. The novel synthesis entails the oxidation of molybdenum in aqueous solutions of excess and limited dopamine (Dopa) hydrochloride via a hydrogen peroxide-initiated process. The transformation of molybdenum under the condition of Dopa excess (Mo:Dopa molar ratio of 1:1) resulted in the formation of a metastable precipitate of polydopamine (PDopa) spheres encapsulated by Dopa-preintercalated molybdenum oxide, (Dopa)xMoOy@PDopa. Hydrothermal treatment (HT) of (Dopa)xMoOy@PDopa precursor was concomitant with concurrent Dopa carbonization and molybdenum reduction processes, resulting in a formation of spherical matrices of Dopa-derived carbon decorated by MoO2 nanoplatelets (HT-MoO2/C), as determined through FTIR spectroscopy, Raman spectroscopy, and SEM imaging. Annealing (An) of HT-MoO2/C at 600°C under argon atmosphere (AnHT-MoO2/C) led not only to improvements in MoO2 crystallinity, but also to an increased oxidation state of molybdenum and a facilitated interaction between molybdenum-based and Dopa-derived components, resulting in an intimate MoO2/C heterointerface. Consequently, while both HT-MoO2/C and AnHT-MoO2/C showed reversible intercalation-type behavior when evaluated as electrodes versus Li/Li+ in nonaqueous lithium-ion cells, AnHT-MoO2/C demonstrated higher capacities, enhanced capacity retention, better rate capability, and lower charge transfer resistance. The AnHT-MoO2/C electrode showed an initial specific capacity of 260 mAh/g and 67% capacity retention after 50 cycles at 10 mA/g, compared to an initial specific capacity of 235 mAh/g and 47% capacity retention shown by HT-MoO2/C at the same current density. Furthermore, in rate capability experiments, HT-MoO2/C and AnHT-MoO2/C delivered specific capacities of 93 mAh/g and 120 mAh/g respectively at 100 mA/g. When molybdenum was transformed in the presence of Dopa deficit (Mo:Dopa molar ratio of 5:1), a (Dopa)xMoOy powder precursor was isolated, and subsequent hydrothermal treatment of this precursor produced an MoO3 material with carbonized Dopa molecules, HT-MoO3/C. Reference α-MoO3 electrodes (α-MoO3-ref) were synthesized similarly but in the absence of Dopa molecules in the initial sol-gel reaction. The appearance of characteristic D and G bands in the Raman spectra and distinct vibrational modes in the FTIR spectra of HT-MoO3/C confirmed the presence of carbon in its structure. SEM images showed a uniform nanobelt morphology with fragmentation due to interactions between interlayer Dopa and MoO3 layers under the conditions of hydrothermal treatment. HT-MoO3/C delivered a second-cycle capacitance of 141.4 F/g when cycled at 2 mV/s in a -0.25–0.70 V versus Ag/AgCl potential window in 5M ZnCl2 electrolyte, while α-MoO3-ref delivered a nearly two-fold smaller second-cycle capacitance of 76.1 F/g under the same conditions. HT-MoO3/C also showed increased capacitance compared to α-MoO3-ref when cycled at increasing sweep rates up to 20 mV/s. The superior performance of HT-MoO3/C prompted a study of the electrode in an expanded potential window, based on previous reports in which MoO3 showed electrochemical activity at negative potentials versus Ag/AgCl. The HT-MoO3/C electrode exhibited a capacitance of 347.6 F/g on the second cycle when cycled between -0.85–1.00V versus Ag/AgCl at 2 mV/s in 5M ZnCl2 electrolyte. This work demonstrates a new strategy to improve the electrochemical performance of transition metal oxide electrodes for next-generation energy storage systems. Integration of oxides with carbon through the wet chemistry synthesis approaches that involve carbonization of organic molecules can be used to control oxide crystal phase and heterointerfaces leading to improved charge transfer and energy storage properties.

For satisfying the efficient storage and processing of massive data in the information technology era, spintronic device attracts tremendous attention due to its low power consumption and non-volatile feature. Spin source material, which can efficiently generates spin current, is an important constituent of novel spin-orbit torque device. The efficiency of spin current generation in spin source materials directly determines the performance of various spintronic devices. In the nearly two decades, great progress has been achieved in exploring high-efficient spin source material systems, as well as understanding the relevant physical mechanisms. A wide variety of materials are explored ranging from the traditional heavy metal and semiconductors to topological insulators and 2D materials. Recently, the material family of transition metal oxides attracts tremendous attention due to its efficient and highly tunable charge-spin conversion intimately related to its emerging novel quantum states and electronic structure. The mechanism of charge-spin conversion generally have two contributions from the bulk spin Hall effect and the spin-momentum locked interface with inversion symmetry breaking. Novel electronic structure such as the topological band structure and spin-momentum locked surface states can realize efficient charge-spin conversion. For example, the Weyl points in SrRuO₃ and the topological Dirac nodal line in SrIrO₃ are predicted to give rise to large Berry curvature and the corresponding spin Hall conductance; the topological surface states can generate spin accumulation due to spin-momentum locking; the Rashba states at the oxide interface such as the 2D electron gas in SrTiO₃ and KTaO₃ can generate spin current by Rashba-Edelstein effect. Furthermore, the entanglement of various degrees of freedom, including spin, charge, lattice and orbit in transition metal oxides lead to the electronic structure highly tunable by various methods including gate voltage, substrate constraint, thickness, interface engineering <em>etc</em>. Therefore, the charge-spin conversion in transition metal oxides is of great interest for both fundamental research in modulation of novel electronic structure and exploring its promising potential in future spintronic devices. In this review, we focus on introducing the aspects of exotic electronic structures, spin transport mechanism, charge-spin interconversion characterization, efficiency and manipulation in TMOs, and giving a perspective about the future development trend.

ABSTRACTRecently there has been much interest in reacting vanadium oxides hydrothermally with cationic surfactants to form novel layered compounds. A series of new transition metal oxides, however, has also been formed at or near room temperature in open containers. Synthesis, characterization, and proposed mechanisms of formation are the focus of this work. Low temperature reactions of vanadium pentoxide and ammonium (DTA) transition metal oxides with long chain amine surfactants, such as dodecyltrimethylammonium bromide yielded interesting new products many of which are layered phases. DTA4H2V10O28•8H2O, a layered highly crystalline phase, is the first such phase for which a single crystal X-ray structure has been determined. The unit cell for this material was found to be triclinic with space group P 1 and dimensions a=9.895(1)Å, b=11.596(1)Å, c=21.924(1)Å, α=95.153(2)°, β=93.778(1)°, and γ= 101.360(1)°. Additionally, we synthesized a dichromate phase and a manganese chloride layered phase, with interlayer spacings of 26.8Å, and 28.7Å respectively. The structure, composition, and synthesis of the vanadium compound are described, as well as the synthesis and preliminary characterization of the new chromium and manganese materials.

Abstract Oxygen defects are essential building blocks for designing functional oxides with remarkable properties, ranging from electrical and ionic conductivity to magnetism and ferroelectricity. Oxygen defects, despite being spatially localized, can profoundly alter global properties such as the crystal symmetry and electronic structure, thereby enabling emergent phenomena. In this work, we achieved tunable metal–insulator transitions (MIT) in oxide heterostructures by inducing interfacial oxygen vacancy migration. We chose the non-stoichiometric VO2-δ as a model system due to its near room temperature MIT temperature. We found that depositing a TiO2 capping layer on an epitaxial VO2 thin film can effectively reduce the resistance of the insulating phase in VO2, yielding a significantly reduced ROFF/RON ratio. We systematically studied the TiO2/VO2 heterostructures by structural and transport measurements, X-ray photoelectron spectroscopy, and ab initio calculations and found that oxygen vacancy migration from TiO2 to VO2 is responsible for the suppression of the MIT. Our findings underscore the importance of the interfacial oxygen vacancy migration and redistribution in controlling the electronic structure and emergent functionality of the heterostructure, thereby providing a new approach to designing oxide heterostructures for novel ionotronics and neuromorphic-computing devices.

ABSTRACTRecent research on the growth and structure of carbide nanorods is reviewed. Carbide nanorods have been prepared by reacting carbon nanotubes with volatile transition metal and main group oxides and halides. Using this approach it has been possible to obtain solid carbide nanorods of TiC, SiC, NbC, Fe3C, and BCx having diameters between 2 and 30 nm and lengths up to 20 µm. Structural studies of single crystal TiC nanorods obtained through reactions of TiO with carbon nanotubes show that the nanorods grow along both [110] and [111] directions, and that the rods can exhibit either smooth or saw-tooth morphologies. Crystalline SiC nanorods have been produced from reactions of carbon nanotubes with SiO and Si-iodine reactants. The preferred growth direction of these nanorods is [111], although at low reaction temperatures rods with [100] growth axes are also observed. The growth mechanisms leading to these novel nanomaterials have also been addressed. Temperature dependent growth studies of TiC nanorods produced using a Ti-iodine reactant have provided definitive proof for a template or topotactic growth mechanism, and furthermore, have yielded new TiC nanotube materials. Investigations of the growth of SiC nanorods show that in some cases a catalytic mechanism may also be operable. Future research directions and applications of these new carbide nanorod materials are discussed.

Transition metal spinel oxides comprised of earth-abundant Mn and Co have long been explored for their use in catalytic reactions and energy storage. However, understanding functional properties can be challenging due to differences in sample preparation and the ultimate structural properties of the materials. Epitaxial thin film synthesis provides a novel means of producing precisely controlled materials to explore the variations reported in the literature. In this work, MnxCo3−xO4 samples from x = 0 to x = 1.28 were synthesized through molecular beam epitaxy and characterized to develop a material properties map as a function of stoichiometry. Films were characterized via in situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, and polarized K-edge x-ray absorption spectroscopy. Mn cations within this range were found to be octahedrally coordinated, in line with an inverse spinel structure. Samples largely show mixed Mn3+ and Mn4+ character with evidence of phase segregation tendencies with the increasing Mn content and increasing Mn3+ formal charge. Phase segregation may occur due to structural incompatibility between cubic and tetragonal crystal structures associated with Mn4+ and Jahn–Teller active Mn3+ octahedra, respectively. Our results help in explaining the reported differences across samples in these promising materials for renewable energy technologies.