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1
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Hopping Conductance in Nanocomposites (Fe_{0.45}Co_{0.45}Zr_{0.10})_{x}(Al_2O_3)_{1 - x} Manufactured by Ion-Beam Sputtering of Complex Target in Ar+O_2 Ambient Gas

100%
Kołtunowicz T., Zhukowski P., Fedotova V., Saad A., Fedotov A.
Acta Physica Polonica A
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2011
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vol. 120
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issue 1
39-42
EN
We report the investigation of a real part of the admittance σ of granular nanocomposites (Fe_{0.45}Co_{0.45}Zr_{0.10})_{x}(Al_2O_3)_{1 - x} with 0.30 < x < 0.70 in the dielectric (hopping) regime. An analysis of the σ(T, f, x) dependences in the as-deposited and annealed films over the temperature 77 K < T < 300 K and frequency 50 < f < 10^6 Hz ranges displayed the predominance of an activation (hopping) conductance mechanism with dσ/ dT > 0 for the samples below the percolation threshold x_{C} ≈ 0.76 ± 0.05. Based on the earlier models for hopping AC conductance, computer simulation of the frequency coefficient α_{f} of hopping conductance depending on the probability of jump p, frequency f, and also on the shape of σ(f) curve was performed. The experimental and simulation results revealed a good agreement.
2
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Low-Temperature DC Carrier Transport in (Co_{0.45}Fe_{0.45}Zr_{0.10})_{x}(Al_2O_3)_{1-x} Nanocomposites Sputtered in Mixed Argon-Oxygen Atmosphere

86%
Svito I., Fedotov A., Saad A., Koltunowicz T., Zukowski P., Bury P.
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vol. 125
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issue 6
1351-1355
EN
This paper studies the temperature dependences (2 < T < 300 K) of the DC conductivity σ(T) for the (Co_{0.45}Fe_{0.45}Zr_{0.10})_x(Al_2O_3)_{1-x} nanocomposites (30 < x < 65 at.%) sputtered in Ar + O_2 atmosphere. It is shown that at temperatures lower than 100-150 K dependences of DC conductance on temperature for all the studied samples are due to the Shklovski-Efros variable range hopping mechanism. It was also observed that σ(x,T) dependences can be attributed to the formation of FeCo-based oxide "shells" around metallic alloy nanoparticles due to incorporation of oxygen in the vacuum chamber during the deposition procedure.
3
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Mechanisms of Carrier Transport in Cu_x(SiO₂)_{1-x} Nanocomposites Manufactured by Ion-Beam Sputtering with Ar Ions

86%
Fedotov A., Mazanik A., Svito I., Saad A., Fedotova V., Czarnacka K., Koltunowicz T.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
883-886
EN
The present paper investigates the temperature/frequency dependences of admittance Z in the granular Cu_x(SiO₂)_{1-x} nanocomposite films around the percolation threshold x_{C} in the temperature range of 4-300 K and frequencies of 20-10⁶ Hz. The behavior of low-frequency ReZ(T) dependences displayed the predominance of electrons hopping between the closest Cu-based nanoparticles for the samples below the percolation threshold x_{C} ≈ 0.59 and nearly metallic behaviour beyond the x_{C}. The high-frequency curves ReZ(f) at temperatures T > 10 K for the samples with x < x_{C} exhibited behavior close to ReZ(f) ≈ f^{-s} with s ≈ 1.0 which is very similar to the known Mott law for electron hopping mechanism. For the samples beyond the percolation threshold (x > x_{C}), the frequency dependences of ReZ(f) displayed inductive-like (not capacitive) behaviour with positive values of the phase shift angles.
4
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Admittance and Permittivity in Doped Layered TlGaSe_2 Single Crystals

86%
Dawood S., Fedotov A., Mammadov T., Zukowski P., Koltunowicz T., Saad A., Drozdov N.
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vol. 125
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issue 6
1267-1271
EN
In doped TlGaSe_2 crystals the phase transitions at low temperatures (100-170 K) were observed using admittance and dielectric spectroscopy in a temperature range of 80-320 K. The admittance and permittivity measurements in the studied samples indicated that after Fe or Tb doping by impurities with concentrations N_{imp} < 0.5 at.% nonequilibrium electronic phase transition is observed. Doping with N_{imp} > 0.5 at.% resulted in full suppression of this phase transition presence.
5
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The Features of Real Part of Admittance in the Nanocomposites (Fe_{45}Co_{45}Zr_{10})_{x}(Al_2O_3)_{100 - x} Manufactured by the Ion-Beam Sputtering Technique with Ar Ions

86%
Kołtunowicz T., Zhukowski P., Fedotova V., Saad A., Larkin A., Fedotov A.
Acta Physica Polonica A
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2011
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vol. 120
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issue 1
35-38
EN
The temperature and frequency dependences of the admittance real part σ (T, f) in granular (Fe_{45}Co_{45}Zr_{10})_{x}(Al_2O_3)_{100 - x} nanocomposite films around the percolation threshold x_{C} were investigated. The behaviour of σ (T, f) vs. the temperature and frequency over the ranges 77-300 K and 50 Hz-1 MHz, respectively, displays the predominance of an activation (hopping) conductance mechanism for the samples below the percolation threshold x_{C} and of a metallic one beyond the x_{C} determined as 54 ± 2 at.%. The mean hopping range d for the nanoparticles diameter D was estimated at different metallic phase content x.
6
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Voltage and Current Resonance in Nanocomposite (FeCoZr)_x(CaF₂)_{100-x} Produced by Ion-Beam Sputtering in Pure Argon Atmosphere

86%
Koltunowicz T., Zukowski P., Bondariev V., Fedotov A., Svito I., Fedotova J., Saad A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
897-900
EN
In this paper the results of investigations of electrical properties of metal-dielectric nanocomposites (FeCoZr)_x(CaF₂)_{100-x} are presented. The samples with the metallic phase content x=45.7 at.% were produced by ion-beam sputtering method in pure argon atmosphere, and subsequently annealed at 398 K for 15 min. The measurements of electrical properties were performed in the frequency range from 50 Hz to 1 MHz. The frequency dependences of phase angle θ, capacity C_{p}, conductivity σ and dielectric loss factor tanδ were measured at seven different temperatures ranging from 148 K to 263 K. It was found that the nanocomposite exhibits the phenomena of voltage resonance and current resonance, characteristic of the conventional RLC circuits with series and parallel connections of elements.
7
Content available remote

Thermoelectric Properties of Ca_3Co_4O_9-Based Ceramics Doped with Fe and/or Y

73%
Fedotov A., Fedotov A., Mazanik A., Svito I., Saad A., Troyanchuk I., Bushinski M., Fedotova V., Zukowski P., Koltunowicz T.
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vol. 125
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issue 6
1344-1347
EN
We describe here structure and temperature dependences of conductivity σ(T), the Seebeck coefficient α(T), thermal conductivity λ(T) and figure-of-merit ZT(T) in Ca_3Co_4O_9 ceramics, doped with Fe and Y, depending on compacting pressure (0.2 or 6 MPa) and temperature (300 < T < 700 K). It is shown that introduction of iron and yttrium to ceramics does not alter the crystalline structure of the material. Increasing the pressure in the compacting process before the additional diffusion annealing leads to a smaller-grained structure and increase σ and λ due to reducing of the synthesized samples porosity. The Seebeck coefficients of nanocomposite ceramics Ca_3Co_{3.9}Fe_{0.1}O_9 and (Ca_{2.9}Y_{0.1})(Co_{3.9}Fe_{0.1})O_9 have linear dependences on temperature is not changed after increase of compacting pressure. Electrical-to-heat conductivity ratio (σ/λ) for the samples compacted at high (6 GPa) pressure increases not more than 20-30% in comparison with ones compacted at low (0.2 GPa) pressure, whereby ZT is increased more than 50%. The main reason for this effect is samples porosity reduction with the compacting pressure increase.
8
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Anisotropic Magnetoresistance of Ni Nanorod Arrays in Porous SiO₂/Si Templates Manufactured by Swift Heavy Ion-Induced Modification

73%
Fedotova J., Ivanou D., Mazanik A., Svito I., Streltsov E., Saad A., Zukowski P., Fedotov A., Bury P., Apel P.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
894-896
EN
In this work anisotropic magnetoresistance in nanogranular Ni films and Ni nanorods on Si(100) wafer substrates was studied in wide ranges of temperature and magnetic field. To produce Ni films and nanorods we used electrochemical deposition of Ni clusters either directly on the Si substrate or into pores in SiO₂ layer on the Si substrate. To produce mesopores in SiO₂ layer, SiO₂/Si template was irradiated by a scanned beam of swift heavy 350 MeV ¹⁹⁷Au²⁶⁺ ions with a fluence of 5×10⁸ cm¯² and then chemically etched in diluted hydrofluoric acid. Pores, randomly distributed in the template have diameters of 100-250 nm and heights about 400-500 nm. Comparison of temperature dependences of resistance and magnetoresistance in Ni films and n-Si/SiO₂/Ni structures with Ni nanorods showed that they are strongly dependent on orientation of magnetic field and current vectors relative to each other and the plane of Si substrate. Moreover, magnetoresistance values in n-Si/SiO₂/Ni nanostructures can be controlled not only by electric field applied along Si substrate but also by additionally applied transversal bias voltage.
9
Content available remote

Magnetoresistance in n-Si/SiO_2/Ni Nanostructures Manufactured by Swift Heavy Ion-Induced Modification Technology

59%
Fedotova J., Ivanou D., Ivanova Y., Fedotov A., Mazanik A., Svito I., Streltsov E., Saad A., Tyutyunnikov S., Kołtunowicz T., Demyanov S., Fedotova V.
Acta Physica Polonica A
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2011
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vol. 120
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issue 1
133-135
EN
A study of magnetotransport in the n-Si/SiO_2/Ni nanostructures with granular Ni nanorods in SiO_2 pores was performed over the temperature range 2-300 K and at the magnetic fields induction up to 8 T. The n-Si/SiO_2/Ni Schottky nanostructures display the enhanced magnetoresistive effect at 25 K due to the impurity avalanche mechanism.
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