Synchrotron X-Ray Study on the Charge Density and Mixed-Valence State for Transition-Metal Oxides.

The evidence for, and the factors determining, the formation of metal-to-metal (m-m) bonds in transition metal oxides, sulphides, halides, and related complexes are discussed. It is proposed that when metals of high preferred valence state are constrained to low formal oxidation states, m-m bonds will form to allow the metal to exercise a higher valency. It is assumed that (n-l)d orbitals are used for such bonds and predictions of the feasibility of m-m bonding are possible by the comparison of the size of such orbitals with the expected inter-metal distances in polymeric metal oxides and halides. It is concluded that binary oxides and halides (excepting fluorides) of the lower oxidation states of Zr, Hf, Nb, Ta, Mo, W, and Re and of a few neighbouring elements will display m-m bonds.

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ChemInform Abstract: SURFACE REDUCTION OF SOME TRANSITION-METAL OXIDES. AN X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF IRON, COBALT, NICKEL, AND ZINC OXIDES

Chemischer Informationsdienst ◽

10.1002/chin.198551013 ◽

1985 ◽

Vol 16 (51) ◽

Author(s):

S. J. COCHRAN ◽

F. P. LARKINS

Keyword(s):

Transition Metal ◽

Metal Oxides ◽

Spectroscopic Study ◽

Transition Metal Oxides ◽

Iron Cobalt ◽

X Ray ◽

Surface Reduction ◽

Zinc Oxides ◽

Cobalt Nickel

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Mixed-valence state of the rare-earth compounds YbXCu4 ( X = Mg, Cd, In, and Sn): Magnetic susceptibility, x-ray diffraction, and x-ray absorption spectroscopy investigations

Physical Review B ◽

10.1103/physrevb.100.245124 ◽

2019 ◽

Vol 100 (24) ◽

Cited By ~ 1

Author(s):

Hiroaki Anzai ◽

Suzuna Ishihara ◽

Hiroto Shiono ◽

Kohei Morikawa ◽

Toshiaki Iwazumi ◽

...

Keyword(s):

Magnetic Susceptibility ◽

Rare Earth ◽

Absorption Spectroscopy ◽

Valence State ◽

Mixed Valence ◽

Rare Earth Compounds ◽

X Ray Diffraction ◽

X Ray ◽

Mixed Valence State ◽

X Ray Absorption

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

Microscopy and Microanalysis ◽

10.1017/s1431927600033377 ◽

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.

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Electret formation in transition metal oxides by electrochemical amorphization

NPG Asia Materials ◽

10.1038/s41427-019-0187-x ◽

2020 ◽

Vol 12 (1) ◽

Cited By ~ 16

Author(s):

Yong-Jin Kim ◽

Chan-Ho Yang

Keyword(s):

Transition Metal ◽

Metal Oxides ◽

Charge Density ◽

Electric Fields ◽

Transition Metal Oxides ◽

Degrees Of Freedom ◽

Permanent Magnets ◽

Underlying Mechanism ◽

Diffusion Reaction ◽

Wide Range

AbstractTransition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs.

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