Stability and magnetism of vacancy in NiO: A GGA+U study

Zhang, Wei-Bing; Yu, Na; Yu, Weiyang; Tang, Bing

doi:10.1140/epjb/e2008-00303-x

Cited by 65 publications

(44 citation statements)

References 43 publications

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“…The above result is supported by theoretical predictions of FM in NiO. Zhang et al 29 reported that half-metallic FM of NiO originates from singly or doubly negatively charged nickel vacancies. There are several experimental works which also confirm the Nivacancy induced FM in NiO nanoparticles.…”

Section: Resultssupporting

confidence: 68%

“…Richardson et al 16 , however, have demonstrated that these moments only have a very slight change by oxidation (to eliminate Ni metal) or mild reduction (to eliminate Ni 3+ ). Up to date, the most widely accepted mechanism is the vacancy induced FM for AF NiO nanomaterials.The evidence of vacancy induced FM in nonmagnetic systems 26,27 implies that vacancies also can play an important role in determining the ferromagnetic behavior of AF nanoparticles like CuO, 7 CoO, 28 and NiO, [29][30][31][32][33][34] but it is still a highly controversial issue, as it is indistinguishable whether the FM is due to cation or anion vacancies effects. As for NiO nanomaterials, the exact origin of FM also remains unresolved, till now.…”

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confidence: 99%

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Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Chen¹,

Chen²,

Zhang³

et al. 2017

ECS J. Solid State Sci. Technol.

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Pure NiO nanoparticles were subjected to isochronal thermal treatments in open air from 100 to 1000 • C. X-ray diffraction (XRD) patterns indicate that all annealed samples exhibit a single phase of face-centered cubic (FCC) crystalline structure, obvious grain growth occurs only above 400 • C and the average crystallite size increases from 20 to 80 nm. X-ray photoelectron spectroscopy (XPS) shows that only very few amount of Ni 3+ and no impurity element have been found in the annealed samples. Positron annihilation measurements reveal that large number of Ni-vacancy defects exist in the grain surface region. These surface defects begin to recover after annealing above 400 • C, and most of them are removed at 1000 • C. Room temperature ferromagnetism is obviously observed for the samples annealed at 100 and 400 • C. The saturation magnetization gradually decreases with the increase of the annealing temperature, and it almost disappears at 800 and 1000 • C. The disappearance of ferromagnetism shows good coincidence with the recovery of Ni-vacancies. Our results suggest that the anomalous ferromagnetic behavior in NiO nanoparticles might be due to the surface Ni-vacancy defects instead of grain size effects. 2 It is well known that the bulk AF materials are magnetically compensated and have zero net magnetic moment in zero applied field, while fine particles of an AF material should display either weak ferromagnetism (FM) or superparamagnetism (SPM).3 Since Richardson and Milligan first reported anomalous magnetic properties in NiO nanoparticles, 4 ferromagnetic behaviors were found in an increasing number of AF nanomaterials. Consequently, it is important to investigate the magnetic mechanism of AF nanomaterials extensively. Among the various nanostructured AF transition metal monoxides, NiO has been widely investigated, because it is a unique metal-deficient p-type semiconductor presenting a wide band-gap (3.6-4.0eV), and its bulk form possesses a relatively high Néel temperature T N (523 K). As a consequence, it can cause high storage density of magnetic recording media due to allowing magnetic stability at very low volumes far above room temperature. 17 In the recent few decades, great efforts have been devoted to exploring the unexpected magnetic properties in NiO nanomaterials, such as large magnetic moments, enhanced coercivity, spin glass freezing and hysteretic loop shifts. However, up to now the underlying mechanism for the FM is still unclear. It has been reported that the FM might come from the surface and finite size effects, or a net magnetic moment probably arises from uncompensated spins. Several models, such as the two-sublattice model, 3 multi-sublattice model, 10 and core-shell model 9,12-14,18-24 have been used to illustrate the anomalous properties of NiO nanoparticles. However, different groups reported that * Electrochemical Society Fellow.z E-mail: czy2004hust@163.com; chenzq@whu.edu.cn; mascher@mcmaster.ca surface effects and size effects on the ferromagnetic properties of the nanomater...

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Section: Resultssupporting

confidence: 68%

mentioning

confidence: 99%

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Chen¹,

Chen²,

Zhang³

et al. 2017

ECS J. Solid State Sci. Technol.

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“…At room temperature, the sample gives rise to a 75 diamagnetic signal (black squares of Figure 3), most of which is due to the substrate. This behavior is consistent with either a diamagnetic film or an antiferromagnetic out -the former case being often observed for bulk substoichiometric oxide, [13] whereas NiO notoriously has the latter character. Upon 80 annealing under argon, however, the material is transformed.…”

supporting

confidence: 81%

Stoichiometry of Nickel Oxide Films Prepared by ALD

Bachmann¹,

Zolotaryov²,

Albrecht³

et al. 2011

Chemical Vapor Deposition

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“…Electronic correlations were also included in a simple rotationally invariant DFT+U version. 24 Plane-wave basis sets were used with energy cutoff of 400 eV. The integration on Brillouin zone was done in 4 × 4 × 1 grid.…”

Section: Methodsmentioning

confidence: 99%

Mechanism Study of Hydrazine Electrooxidation Reaction on Nickel Oxide Surface in Alkaline Electrolyte by In Situ XAFS

Sakamoto¹,

Kishi²,

Yamaguchi³

et al. 2016

J. Electrochem. Soc.

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This study introduces a new insight on the mechanism of selective electrooxidation of hydrazine in alkaline media. The catalytic process takes place on nickel oxide surface of a Ni oxide nano-particle decorated carbon support (NiO/C). The catalyst was synthesized by wet impregnation and a liquid reduction procedure followed by thermal annealing. In-situ X-ray absorption fine structure (XAFS) spectroscopy was used to investigate the reaction mechanism for hydrazine electrooxidation on NiO surface. The spectra of X-ray absorption near-edge structure (XANES) of Ni K-edge indicated that adsorption of OH − on Ni site during the hydrazine electrooxidation reaction. Density functional theory (DFT) calculations were used to elucidate and suggest the mechanism of the electrooxidation and specifically propose the localization of electron density from OH − to 3d orbital of Ni in NiO. It is found that the accessibility of Ni atomic sites in NiO structure is critical for hydrazine electrooxidation. Based on this study, we propose a possible reaction mechanism for selective hydrazine electrooxidation to water and nitrogen taking place on NiO surface as it is applicable to direct hydrazine alkaline membrane fuel cells. Diversification of fuel is important to enhance the versatility of fuel cells as viable power devices for the next generation. Liquid fuel such as methanol, ethanol, borohydride, formic acid, 2-propanol, dimethyl ether and hydrazine are liquid chemical substances that include hydrogen and are considered an energy source in which hydrogen is an electron carrier. The advantages of liquid fuels include, but are not limited to high energy density and ease of handling at both the energy supply and demand sides. In the case of liquid fuel, simple/existing infrastructure, such as conventional petrol stations, is sufficient as for fuel supply, and while the geographic and temporal gap between energy supply and receipt are being filled this would allow to concentrate and leveraging off energy contribution to the expansion of and market penetration of fuel cell technology.Direct hydrazine hydrate fuel cells (DHFCs) utilizing an anion exchange membrane have recently attracted attention as a clean power device. Hydrazine contains no carbon and excretes harmless nitrogen and water by theoretical electroreaction and non-platinum group metal (PGM) catalysts such as Fe, Co, and Ni. These catalysts have been demonstrated for both the anode and cathode electrodes as shown Fig. 1a. The fuel cell vehicle equipped with no PGM as catalysts was demonstrated at SPring-8 in 2013. We believe this demonstration of DHFCs as a power device contributes to the reduction of CO 2 emissions and begins to address the fossil fuel resource problem. If zero CO 2 emission fuel cell vehicles (FCVs), are to be deployed using carbon-free liquid fuel, the emissions of CO 2 would be associated only with the liquid fuel manufacturing facility side and the measures of reduction of CO 2 emission by the transportation sector are would be supported by the depl...

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Stability and magnetism of vacancy in NiO: A GGA+U study

Cited by 65 publications

References 43 publications

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Stoichiometry of Nickel Oxide Films Prepared by ALD

Mechanism Study of Hydrazine Electrooxidation Reaction on Nickel Oxide Surface in Alkaline Electrolyte by In Situ XAFS

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