scholarly journals Coexisting commensurate and incommensurate charge ordered phases in CoO

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Devendra Negi ◽  
Deobrat Singh ◽  
Rajeev Ahuja ◽  
Peter A. van Aken
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Lattice Distortion ◽  
Mixed Valence ◽  
Periodic Lattice ◽  
Strongly Correlated Materials ◽  
Valence States ◽  
Transmission Electron ◽  
Jahn Teller ◽  
Phase Singularities

AbstractThe subtle interplay of strong electronic correlations in a distorted crystal lattice often leads to the evolution of novel emergent functionalities in the strongly correlated materials (SCM). Here, we unravel such unprecedented commensurate (COM) and incommensurate (ICOM) charge ordered (CO) phases at room temperature in a simple transition-metal mono-oxide, namely CoO. The electron diffraction pattern unveils a COM ($$q_{1}$$ q 1 =$$\frac{1}{2}(1,1,{\bar{1}})$$ 1 2 ( 1 , 1 , 1 ¯ ) and ICOM ($$q_{2}=0.213(1,1,{\bar{1}})$$ q 2 = 0.213 ( 1 , 1 , 1 ¯ ) ) periodic lattice distortion. Transmission electron microscopy (TEM) captures unidirectional and bidirectional stripe patterns of charge density modulations. The widespread phase singularities in the phase-field of the order parameter (OP) affirms the abundant topological disorder. Using, density functional theory (DFT) calculations, we demystify the underlying electronic mechanism. The DFT study shows that a cation disordering ($$\mathrm {Co}_{1-\textit{x}}\mathrm {O}, \text {with }{} \textit{x} = 4.17 \%$$ Co 1 - x O , with x = 4.17 % ) stabilizes Jahn-Teller (JT) distortion and localized aliovalent $$\mathrm {Co}^{3+}$$ Co 3 + states in CoO. Therefore, the lattice distortion accompanied with mixed valence states ($$\mathrm {Co}^{3+}, \mathrm {Co}^{2+}$$ Co 3 + , Co 2 + ) states introduces CO in CoO. Our findings offer an electronic paradigm to engineer CO to exploit the associated electronic functionalities in widely available transition-metal mono-oxides.

Cerium oxide nanomaterial with dual antioxidative scavenging potential: Synthesis and characterization

2021 ◽  
pp. 088532822110134
Author(s):  
Sushant Singh ◽  
Udit Kumar ◽  
David Gittess ◽  
Tamil S Sakthivel ◽  
Balaashwin Babu ◽  
...  
Keyword(s):  
Cerium Oxide ◽  
Biological Systems ◽  
Mixed Valence ◽  
Stable Solution ◽  
Ability To Act ◽  
Valence States ◽  
Transmission Electron ◽  
Efficient Reduction ◽  
Rich Media

Many studies have linked reactive oxygen species (ROS) to various diseases. Biomedical research has therefore sought a way to control and regulate ROS produced in biological systems. In recent years, cerium oxide nanoparticles (nanoceria, CNPs) have been pursued due to their ability to act as regenerative ROS scavengers. In particular, they are shown to have either superoxide dismutase (SOD) or catalase mimetic (CAT) potential depending on the ratio of Ce3+/Ce4+ valence states. Moreover, it has been demonstrated that SOD mimetic activity can be diminished by the presence of phosphate, which can be a problem given that many biological systems operate in a phosphate-rich environment. Herein, we report a CNP formulation with both SOD and catalase mimetic activity that is preserved in a phosphate-rich media. Characterization demonstrated a highly dispersed, stable solution of uniform-sized, spherical-elliptical shaped CNP of 12 ± 2 nm, as determined through dynamic light scattering, zeta potential, and transmission electron microscopy. Mixed valence states of Ce ions were observed via UV/Visible spectroscopy and XPS (Ce3+/Ce4+ > 1) (Ce3+∼ 62%). X-ray diffraction and XPS confirmed the presence of oxygen-deficient cerium oxide (CeO2-x) particles. Finally, the CNP demonstrated very good biocompatibility and efficient reduction of hydrogen peroxide under in-vitro conditions.

Valence Mapping of Particulate 3D-Transition Metal Oxides Using Energyfiltered Transmission Electron Microscopy

2000 ◽  
Vol 6 (S2) ◽  
pp. 176-177
Author(s):  
R.M. Stroud ◽  
J.H. Scott
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Data Extraction ◽  
Mixed Valence ◽  
Charge Localization ◽  
Transmission Electron ◽  
Critical Issues

Particulate, mixed-valence transition metal oxides are frequently used for battery, catalytic and magnetic applications. For example, the Li ion exchange battery exploits charge transfer of mixed Mn+3, Mn+4 materials. Charge localization and phase separation, especially at particle surfaces, are critical issues for determining the materials’ useful properties, be it catalytic activity or saturation magnetization. The ability to image the charge localization and correlate this with crystallographic information would be extremely useful in the study of this class of materials. Using energy-filtered transmission electron microscopy (EFTEM), valence maps of Mn and Co with a ∼ 2 nm scale have been obtained for bulk samples. In principal this technique can de directly extended to the case of particulate samples, however there are some additional experimental challenges, such as thickness and edge effects, that must be addressed. We demonstrate here the feasibility of valence mapping of particulate samples, and discuss the factors that limit quantitative data extraction from the maps.

Synthesis, characterization, X-ray structure, and mixed-valence states of trans-dichlorotin(IV)-5,10,15,20-tetraferrocenylporphyrin

2011 ◽  
Vol 15 (07n08) ◽  
pp. 612-621 ◽  
Author(s):  
Pavlo V. Solntsev ◽  
Ben D. Neisen ◽  
Jared R. Sabin ◽  
Nikolay N. Gerasimchuk ◽  
Victor N. Nemykin
Keyword(s):  
Density Functional ◽  
Mixed Valence ◽  
Nir Spectroscopy ◽  
Density Functional Theory Calculations ◽  
Chemical Oxidation ◽  
Functional Theory ◽  
X Ray ◽  
Valence States ◽  
In Trans

Reaction between H2TFcP (TFcP2- is a dianion of 5,10,15,20-tetraferrocenylporphyrin) with tin(II) chloride results in formation of the trans- Cl2SnTFcP complex, which was characterized by UV-vis, MCD, 1H and 13C NMR, and APCI MS methods. X-ray single crystal analysis was used to determine the structure of the target compound. Crystallography reveals a very unusual α,α,β,β-conformation of the ferrocene groups and largely planar structure of the porphyrin macrocycle. Density functional theory calculations predict that the HOMO in trans- Cl2SnTFcP is predominantly ferrocene centered, while LUMO is primarily localized over the porphyrin core. Redox properties of the trans- Cl2SnTFcP complex were investigated using electrochemical (CV and DPV), spectroelectrochemical, and chemical oxidation approaches. Electrochemical experiments conducted in low-polarity solvent using non-coordinating electrolyte reveal the sequential oxidation of ferrocene substituents along with porphyrin-based single-electron oxidation and reduction processes. The first ferrocene oxidation process is separated by 130 mV from the next three ferrocene based oxidations, which are more closely spaced. Mixed-valence [trans- Cl2SnTFcP]+ was generated in situ by spectroelectrochemical and chemical oxidation approaches and characterized by UV-vis-NIR spectroscopy.

scholarly journals Intermediate Band Studies of Substitutional V2+, Cr2+, and Mn2+ Defects in ZnTe Alloys

2020 ◽  
Vol 10 (24) ◽  
pp. 8937
Author(s):  
Jen-Chuan Tung ◽  
Bang-Wun Lin ◽  
Po-Liang Liu
Keyword(s):  
Energy Density ◽  
Transition Metal ◽  
First Principles ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Emission Spectra ◽  
Total Energy Density ◽  
Energy Density Functional ◽  
Intermediate Band ◽  
Jahn Teller

We present first-principles total-energy density functional calculations to study the intermediate band states of substitutional V2+, Cr2+, and Mn2+ ions in ZnTe alloys. The intermediate band states of substitutional transition metal defects of TM2+xZn1−xTe (TM = V, Cr, Mn) alloys are examined as their atomic, structural, and electronic analysis. Our findings show that the scissor-corrected transitions due to Jahn-Teller effects lead to the wavelengths 2530 nm and 2695 nm in the emission spectra. Our findings agree with previously reported experimental results.

Mapping The Valence States of Transition Metals Across Interfaces By Energy-Filtered Tem

1999 ◽  
Vol 5 (S2) ◽  
pp. 102-103 ◽  
Author(s):  
Z.L. Wang ◽  
J. Bentle ◽  
N.D. Evans
Keyword(s):  
Transition Metal ◽  
Transition Metal Oxides ◽  
Valence State ◽  
Experimental Approach ◽  
White Line ◽  
State Information ◽  
Valence States ◽  
Transmission Electron ◽  
Line Intensity Ratio ◽  
Electron Energy Loss

Some properties of transition metal oxides are related to the presence of elements with mixed valences. In electron energy-loss spectroscopy (EELS), the L or M ionization edges of transition-metal, rare-earth and actinide elements usually display sharp threshold peaks known as white-lines. EELS experiments have shown that a change in cation valence state introduces a significant change in the White-line intensity ratio [1]. With the use of valence state information provided by the white lines, an experimental approach is demonstrated here to map the valence state distributions of Mn and Co using an energy-filtered transmission electron microscope (TEM). A spatial resolution of ˜ 2 nm has been achieved. This technique should be particularly useful in studying valence states of cations in magnetic oxides.To map the distribution of ionization states, an energy window of ˜ 10 eV in width is required to isolate the L3 from L2 white lines (Figure 1).

scholarly journals Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS2

IUCrJ ◽  
2020 ◽  
Vol 7 (5) ◽  
pp. 913-919
Author(s):  
Duan Zhang ◽  
Yecun Wu ◽  
Yu-Hsin Su ◽  
Ming-Chien Hsu ◽  
Cormac Ó Coileáin ◽  
...  
Keyword(s):  
Transition Metal ◽  
Charge Density ◽  
Lattice Distortion ◽  
Electronic Band Structure ◽  
Density Wave ◽  
Charge Density Waves ◽  
Optical Methods ◽  
Periodic Lattice ◽  
Density Waves ◽  
Electronic Band

Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron–electron and electron–phonon interactions, can lead to a new type of electronic band structure. Bulk 2H-TaS2 is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS2 and the transition temperature can reach 140 K, which is much higher than that in the bulk. The degenerate breathing and wiggle modes of 2H-TaS2 originating from the periodic lattice distortion are probed by optical methods. The results open an avenue to investigating charge density wave phases in two-dimensional transition metal dichalcogenides and will be helpful for understanding and designing devices based on charge density waves.

scholarly journals Pyrene Coating Transition Metal Disulfides as Protection from Photooxidation and Environmental Aging

Nanomaterials ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 363 ◽  
Author(s):  
Ruben Canton-Vitoria ◽  
Yuman Sayed-Ahmad-Baraza ◽  
Bernard Humbert ◽  
Raul Arenal ◽  
Christopher Ewels ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Transition Metal ◽  
Density Functional ◽  
Fluorescence Emission ◽  
Density Functional Theory Calculations ◽  
Ambient Conditions ◽  
One Pot ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Environmental Aging

Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical properties of TMD/pyrene are assessed via electronic absorption and fluorescence emission spectroscopy. High-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy confirms extensive pyrene surface coverage, with density functional theory calculations suggesting a strongly bound stable parallel-stacked pyrene coverage of ~2–3 layers on the TMD surfaces. Raman spectroscopy of exfoliated TMDs while irradiating at 0.9 mW/4 μm2 under ambient conditions shows new and strong Raman bands due to oxidized states of Mo and W. Yet remarkably, under the same exposure conditions TMD/pyrene remain unperturbed. The current findings demonstrate that pyrene physisorbed on MoS2 and WS2 acts as an environmental barrier, preventing oxidative surface reactions in the TMDs catalyzed by moisture, air, and assisted by laser irradiation. Raman spectroscopy confirms that the hybrid materials stored under ambient conditions for two years remained structurally unaltered, corroborating the beneficial role of pyrene for not only hindering oxidation but also inhibiting aging.

Electronic Structures in LaTiO3/LaAlO3 Multilayers

2013 ◽  
Vol 771 ◽  
pp. 7-11 ◽  
Author(s):  
Er Jun Kan
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Orbital Ordering ◽  
Crystal Field Theory ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Important Direction ◽  
Jahn Teller Distortion

We demonstrate the existence of a hidden degree of freedom controlling the orbitalordering in [LaTiO1/[LaAlO5 multilayers with comprehensive density-functional theorycalculations. The orbitals of two-dimensional (2D) 3d1state of Ti atoms in the multilayers alwayscontain large dxy components, which is unexpected from crystal field theory (first Jahn-Tellerdistortion). The competition between first and second Jahn-Teller distortion induces variousmagnetic properties. Thus, transition-metal oxides/non-transition-metal oxides multilayers mayprovide an important direction to manipulate the spin and orbital ordering in magnetic materials.

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