Near Edge X-ray Absorption Fine Structure Spectroscopy Studies of Single-Crystalline V<sub>2</sub>O<sub>5</sub> Nanowire Arrays

Velázquez, Jesús M.; Jaye, Cherno; Fischer, Daniel A.; Banerjee, Sarbajit

doi:10.1021/jp900809y

Cited by 64 publications

(112 citation statements)

References 46 publications

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“…Figure 3d represents the least lithiated domains within this sample and is weighted most strongly at the periphery of the nanowire; based on the ensemble spectra depicted in Fig. 1e and previous angle-resolved spectra acquired for V 2 O 5 nanowires33, an extent of lithiation in the broad range 0.1< x< 0.5 can be surmised. It is noteworthy that the intensities at the V L III edge for the lithiated sample are substantially diminished as compared with unlithiated and delithiated V 2 O 5 as a result of state blocking; occupation of conduction band states diminishes the intensity of the low-energy XANES features.…”

Section: Resultsmentioning

confidence: 51%

“…Assignments of the spectral features illustrated in Supplementary Fig. 1 are derived from DFT modelling and are further corroborated by angle-resolved XANES experiments (wherein the modulation in the intensity of resonances as a function of the polarization reflects the orbital symmetry of the final states)303334.…”

Section: Resultsmentioning

confidence: 60%

“…Despite convoluting multiplet effects, restricted open-shell configuration interaction with singles calculations30 indicate that the first two sharp resonances at 515.6 and 516.8 eV, respectively, correspond to final states that have relatively ‘pure' V 3 d xy and 3 d xz / yz character and indeed angle-resolved XANES studies bear out these proposed orbital symmetries303334. In contrast, the O K-edge is not convoluted by multiplet effects and can be clearly distinguished as three sets of transitions from O 1 s core levels to (a) O 2 p x and 2 p y states that engage in π interactions with the t 2g (V 3 d xz , 3 d xy and 3 d yz ) states of the metal cations (at 529.7 eV); overlapping σ states that represent direct end-on hybridization of (b) O 2 p x and 2 p y with V 3 d x 2 – y 2 states at 531.6 eV and (c) O 2 p z with V 3 d z 2 states at 533.1 eV.…”

Section: Resultsmentioning

confidence: 99%

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Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

et al. 2016

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The rapid insertion and extraction of Li ions from a cathode material is imperative for the functioning of a Li-ion battery. In many cathode materials such as LiCoO2, lithiation proceeds through solid-solution formation, whereas in other materials such as LiFePO4 lithiation/delithiation is accompanied by a phase transition between Li-rich and Li-poor phases. We demonstrate using scanning transmission X-ray microscopy (STXM) that in individual nanowires of layered V2O5, lithiation gradients observed on Li-ion intercalation arise from electron localization and local structural polarization. Electrons localized on the V2O5 framework couple to local structural distortions, giving rise to small polarons that serves as a bottleneck for further Li-ion insertion. The stabilization of this polaron impedes equilibration of charge density across the nanowire and gives rise to distinctive domains. The enhancement in charge/discharge rates for this material on nanostructuring can be attributed to circumventing challenges with charge transport from polaron formation.

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Section: Resultsmentioning

confidence: 51%

Section: Resultsmentioning

confidence: 60%

Section: Resultsmentioning

confidence: 99%

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Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

et al. 2016

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“…In past angledependent NEXAFS studies of oriented V 2 O 5 nanowire arrays, we have been able to experimentally verify that the split-off conduction band is primarily 3d xy in origin. 41 Figure 6b shows angle-resolved O K-edge NEXAFS spectra for the δ-Ag x V 2 O 5 nanowires. In our polarized NEXAFS experiments, an incident photon angle of 90°(normal incidence) is perpendicular to the basal plane of the pressed sample (and thus the electric field vector lies parallel to the V 2 O 5 layers); this allows us to selectively probe orbitals lying along the crystallographic ab plane.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Electronic Phase Transitions of δ-Ag_xV₂O₅ Nanowires: Interplay between Geometric and Electronic Structures

et al. 2014

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Vanadium oxide bronzes, with the general formula M x V 2 O 5 , provide a wealth of compositions and frameworks where strong electron correlation can be systematically (albeit thus far only empirically) tuned. In this work, we report the synthesis of single-crystalline δ-Ag 0.88 V 2 O 5 nanowires and unravel pronounced electronic phase transitions induced in response to temperature and applied electric field. Specifically, a pronounced semiconductor−semiconductor transition is evidenced for these materials at ca. 150 K upon heating, and a distinctive insulator−conductor transition is observed upon application of an in-plane voltage. An orbital-specific picture of the mechanistic basis of the phase transitions is proposed using a combination of density functional theory (DFT) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Structural refinements above and below the transition temperature, angle-resolved O K-edge NEXAFS spectra, and DFT calculations suggest that the electronic phase transitions in these 2D frameworks are mediated by a change in the overlap of d xy orbitals. ■ INTRODUCTIONElectronic phase transitions accompanied by dramatic changes of electrical conductivity are of great fundamental interest, and while defining design principles remain to be elucidated, such phenomena are often manifested in materials characterized by structural or electronic instabilities. 1−4 Beyond the fundamental allure of developing a mechanistic description of abrupt changes in physical properties, such phase transitions are also of great practical interest for designing new computing vectors (such as Mott field-effect transistors) and for applications spanning the range from memristors, electromagnetic modulators, and thermal switches to neural networks and electrochromic/thermochromic coatings. 1,3 Electronic phase transitions induced in materials as a result of thermal, electrical, mechanical, or magnetic stimuli can be underpinned by a wide range of mechanisms, such as electron−electron correlation (the Mott−Hubbard picture), electron−phonon coupling (such as Peierl's distortion of the atomistic structure), and disorder (Anderson's localization). 3,5 While considerable interest has focused on the canonical metal−insulator transition material VO 2 , the relatively large structural transformation (and concomitant elastic and strain effects), sluggish relaxation dynamics of the metal → insulator transition, and impediments to decoupling the structural progression from the electronic transition in VO 2 have spurred increasing interest in the discovery of other materials exhibiting pronounced electronic phase transitions at relatively high temperatures. Vanadium oxide bronzes, with the general formula M x V 2 O 5 , provide a richly diversified set of compositions and compounds, where strong electron correlation can be systematically (albeit thus far only empirically) tuned. 6−13 In this work, we report the synthesis of single-crystalline δ-Ag 0.88 V 2 O 5 nanowires, examine the electronic structure of this m...

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“…The samples were mounted with a random orientation on carbon tape on copper plates. This implies that no polarization‐dependent effects should be seen, as in oriented nanowire arrays . The XAS measurements were conducted at the Spherical Grating Monochromator (SGM) beamline at the Canadian Light Source in Saskatoon, Canada .…”

Section: Methodsmentioning

confidence: 99%

Structure‐Induced Switching of the Band Gap, Charge Order, and Correlation Strength in Ternary Vanadium Oxide Bronzes

Tolhurst

Andrews

Leedahl

et al. 2017

Chemistry A European J

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Recently, V O nanowires have been synthesized as several different polymorphs, and as correlated bronzes with cations intercalated between the layers of edge- and corner- sharing VO octahedra. Unlike extended crystals, which tend to be plagued by substantial local variations in stoichiometry, nanowires of correlated bronzes exhibit precise charge ordering, thereby giving rise to pronounced electron correlation effects. These developments have greatly broadened the scope of research, and promise applications in several frontier electronic devices that make use of novel computing vectors. Here a study is presented of δ-Sr V O , expanded δ-Sr V O , exfoliated δ-Sr V O and δ-K V O using a combination of synchrotron soft X-ray spectroscopy and density functional theory calculations. The band gaps of each system are experimentally determined, and their calculated electronic structures are discussed from the perspective of the measured spectra. Band gaps ranging from 0.66 ± 0.20 to 2.32 ± 0.20 eV are found, and linked to the underlying structure of each material. This demonstrates that the band gap of V O can be tuned across a large portion of the range of greatest interest for device applications. The potential for metal-insulator transitions, tuneable electron correlations and charge ordering in these systems is discussed within the framework of our measurements and calculations, while highlighting the structure-property relationships that underpin them.

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Near Edge X-ray Absorption Fine Structure Spectroscopy Studies of Single-Crystalline V₂O₅ Nanowire Arrays

Cited by 64 publications

References 46 publications

Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

Electronic Phase Transitions of δ-Ag_xV₂O₅ Nanowires: Interplay between Geometric and Electronic Structures

Structure‐Induced Switching of the Band Gap, Charge Order, and Correlation Strength in Ternary Vanadium Oxide Bronzes

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Near Edge X-ray Absorption Fine Structure Spectroscopy Studies of Single-Crystalline V2O5 Nanowire Arrays

Cited by 64 publications

References 46 publications

Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

Electronic Phase Transitions of δ-AgxV2O5 Nanowires: Interplay between Geometric and Electronic Structures

Structure‐Induced Switching of the Band Gap, Charge Order, and Correlation Strength in Ternary Vanadium Oxide Bronzes

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Near Edge X-ray Absorption Fine Structure Spectroscopy Studies of Single-Crystalline V₂O₅ Nanowire Arrays

Electronic Phase Transitions of δ-Ag_xV₂O₅ Nanowires: Interplay between Geometric and Electronic Structures