An X-band Co2+ EPR study of Zn1−Co O (x=0.005–0.1) nanoparticles prepared by chemical hydrolysis methods using diethylene glycol and denaturated alcohol at 5 K

Kumar

2019

Ind. Eng. Chem. Res.

175

ZnO nanoparticles are still a hot area for research even after ample work has been done by researchers across the world. It is a versatile material for doping of different transition metals among other metal oxides. Having a large family of morphological structures, high electron mobility, and n-type carrier defects, it is suitable for a number of applications such as memory devices, spintronics, optoelectronic devices, solar cells, and sensors. Here, we have emphasized a review of the effects of transition metal (TM) doping on the different physical properties of ZnO nanoparticles and their applications. We have gone through some theoretical models which were used by most of the researchers for explaining the variations in physical properties. Explanation of the sensing, photocatalytic, and optoelectronic processes in different classes of devices is briefly described. Lastly, the comparative studies of different devices are also made available for clear understanding.

Section: Epr (Electron Paramagnetic Resonance)mentioning

confidence: 99%

Section: Structure Of Transition Metal (Tm)-doped Znomentioning

confidence: 99%

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Progress on Transition Metal-Doped ZnO Nanoparticles and Its Application

Kumar

2019

Ind. Eng. Chem. Res.

175

“…Besides this single-Co 2+ signal, some other weak ESR lines are detected [black marks in Fig. 1(b)], previously seen in several other ESR studies on ZnO:Co NP powder [32][33][34] but not analyzed or assigned to a specific center(s). In the following, these weak ESR lines are investigated and are demonstrated to arise from weakly coupled Co 2+ -Co 2+ pairs with almost isotropic Heisenberg exchange coupling.…”

Section: A Esr Experiments and Modelingmentioning

confidence: 62%

Zero-field magnetic resonance of cobalt ion pairs in ZnO nanocrystals

Marin

Tiwari²,

Bertaina³

et al. 2022

Phys. Rev. B

Cobalt-doped ZnO nanoparticles (NPs) with different Co concentrations are investigated by means of Xand Q-band electron spin resonance (ESR) near liquid-helium temperature in both parallel and perpendicular modes. The high crystal quality of the NPs allows for the hyperfine-structure resolution within the single Co 2+ ions' ESR powder spectra. Depending on cobalt concentration, common additional weak ESR lines are detected which are here demonstrated to arise from some Co 2+ high-spin pairs with a distance of about 4-6 Å. ESR simulations show that these 3/2 spin pairs are weakly coupled by an isotropic Heisenberg Hamiltonian with either ferromagnetic or antiferromagnetic J coupling constants, almost identical to those previously detected in bulk and microwire ZnO:Co. The presence of substantial (axial) single-ion anisotropy in ZnO:Co makes the different pairs' resonance positions strongly depending on the J value. For resonance frequency ν in the microwave range, four cobalt pairs can satisfy the condition |J| ∼ hν/3 to resonate at almost zero magnetic field. Such near-zero-field transitions notably resonate in the parallel ESR mode, which is the signature of the gapped nonlinear Zeeman effect, which is of particular interest for highly stable atomic-clock transitions.

“…As expected, no prominent paramagnetic signal under open-circuit conditions can be observed. Increasing the potential to 1.35 V, the resonance with g ~4 can be observed, corresponding to the Co 2 +species [32,33]. Moreover, two broad resonances with g ~4.372 and g ~2.14 can be observed at 1.39 V, which can be assigned to the Co 4 + species [19,34].…”

mentioning

confidence: 92%

Intermolecular Energy Gap‐Induced Formation of High‐Valent Cobalt Species in CoOOH Surface Layer on Cobalt Sulfides for Efficient Water Oxidation

et al. 2022

Transition metal-based electrocatalysts will undergo surface reconstruction to form active oxyhydroxide-based hybrids, which are regarded as the "truecatalysts" for the oxygen evolution reaction (OER). Much effort has been devoted to understanding the surface reconstruction, but little on identifying the origin of the enhanced performance derived from the substrate effect. Herein, we report the electrochemical synthesis of amorphous CoOOH layers on the surface of various cobalt sulfides (CoS α ), and identify that the reduced intermolecular energy gap (Δ inter ) between the valence band maximum (VBM) of CoOOH and the conduction band minimum (CBM) of CoS α can accelerate the formation of OER-active high-valent Co 4 + species. The combination of electrochemical and in situ spectroscopic approaches, including cyclic voltammetry (CV), operando electron paramagnetic resonance (EPR) and Raman, reveals that Co species in the CoOOH/Co 9 S 8 are more readily oxidized to CoO 2 /Co 9 S 8 than in CoOOH and other CoOOH/CoS α . This work provides a new design principle for transition metal-based OER electrocatalysts.