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Local structure and paramagnetic properties of the nanostructured carbonaceous material shungite.

Krasnovyd SV, Konchits AA, Shanina BD, Valakh MY, Yanchuk IB, Yukhymchuk VO, Yefanov AV, Skoryk MA - Nanoscale Res Lett (2015)

Bottom Line: It is found from the Raman data that carbon fraction is formed from sp(2)-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples.High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes.The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

View Article: PubMed Central - PubMed

Affiliation: V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, 03028 Kyiv, Ukraine.

ABSTRACT
Using a scanning electron microscopy, elemental analysis, electron paramagnetic resonance, and Raman scattering methods, two types of the shungite materials (Sh-II from Zazhogino deposit and shungite from a commercial filter (ShF)), with different carbon content and porosity, are studied in this work. It was established by scanning electron microscopy data that the structure of the shungite samples is formed by a micron-size agglomeration of carbon and silicon dioxide clusters. It is found from the Raman data that carbon fraction is formed from sp(2)-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples. High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes. Big clusters give the conduction electron spin resonance signal with a Dysonian line shape with variable g-factor and line width. The careful search of the nature of two other narrow electron paramagnetic resonance signals in shungite, which used to be prescribed to fullerene-like molecules, is fulfilled. Here, it is shown that the oxygen-deficient E'γ centers are responsible for these signals. A strong correlation is revealed between the concentration of Е'γ centers and the line width of conduction electron spin resonance signal, which occurs under annealing process of the samples at T = 570 K. The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

No MeSH data available.


Theoretical description of the experimental spectrum (Figure3, curve 2). The dotted line indicates the position Hres for conduction electrons.
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Fig4: Theoretical description of the experimental spectrum (Figure3, curve 2). The dotted line indicates the position Hres for conduction electrons.

Mentions: In describing the experimental spectrum, as it is shown in Figure 4, we used the theoretical expression, given in [17,18] for condition d ≫ δ, δe, where d is the thickness of the sample, δ is the skin layer thickness determined by the conductivity and the microwave field frequency of the sample, and δe is the electron diffusion path for spin relaxation time T2. In this case, the EPR line shape is determined only by a single parameter R2 = TD/T2 = (δ/δe)2. The resonance field Hres does not coincides with position at the magnetic field H, where amplitude of the derivative of absorption signal is equal to zero, as soon as a signal is a combination of absorption and dispersion. Consequently, g-factor of free electron can be found only after fitting the calculated spectrum to the experimental one. By this reason, Hres is determined only after the fitting as a point at the H axis, which corresponds to point zero at the upper dimensionless axis in Figure 4.Figure 4


Local structure and paramagnetic properties of the nanostructured carbonaceous material shungite.

Krasnovyd SV, Konchits AA, Shanina BD, Valakh MY, Yanchuk IB, Yukhymchuk VO, Yefanov AV, Skoryk MA - Nanoscale Res Lett (2015)

Theoretical description of the experimental spectrum (Figure3, curve 2). The dotted line indicates the position Hres for conduction electrons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385026&req=5

Fig4: Theoretical description of the experimental spectrum (Figure3, curve 2). The dotted line indicates the position Hres for conduction electrons.
Mentions: In describing the experimental spectrum, as it is shown in Figure 4, we used the theoretical expression, given in [17,18] for condition d ≫ δ, δe, where d is the thickness of the sample, δ is the skin layer thickness determined by the conductivity and the microwave field frequency of the sample, and δe is the electron diffusion path for spin relaxation time T2. In this case, the EPR line shape is determined only by a single parameter R2 = TD/T2 = (δ/δe)2. The resonance field Hres does not coincides with position at the magnetic field H, where amplitude of the derivative of absorption signal is equal to zero, as soon as a signal is a combination of absorption and dispersion. Consequently, g-factor of free electron can be found only after fitting the calculated spectrum to the experimental one. By this reason, Hres is determined only after the fitting as a point at the H axis, which corresponds to point zero at the upper dimensionless axis in Figure 4.Figure 4

Bottom Line: It is found from the Raman data that carbon fraction is formed from sp(2)-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples.High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes.The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

View Article: PubMed Central - PubMed

Affiliation: V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, 03028 Kyiv, Ukraine.

ABSTRACT
Using a scanning electron microscopy, elemental analysis, electron paramagnetic resonance, and Raman scattering methods, two types of the shungite materials (Sh-II from Zazhogino deposit and shungite from a commercial filter (ShF)), with different carbon content and porosity, are studied in this work. It was established by scanning electron microscopy data that the structure of the shungite samples is formed by a micron-size agglomeration of carbon and silicon dioxide clusters. It is found from the Raman data that carbon fraction is formed from sp(2)-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples. High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes. Big clusters give the conduction electron spin resonance signal with a Dysonian line shape with variable g-factor and line width. The careful search of the nature of two other narrow electron paramagnetic resonance signals in shungite, which used to be prescribed to fullerene-like molecules, is fulfilled. Here, it is shown that the oxygen-deficient E'γ centers are responsible for these signals. A strong correlation is revealed between the concentration of Е'γ centers and the line width of conduction electron spin resonance signal, which occurs under annealing process of the samples at T = 570 K. The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

No MeSH data available.