T.N. Koltunowicz

Negative capacitance in (FeCoZr)–(PZT) nanocomposite films

In this work, attention was focused on the inductive contribution to the real part of admittance G(T, f) in (Fe0.45Co0.45Zr0.10)x(PZT)(1−x) nanocomposite films deposited in a mixed argon‐oxygen atmosphere. The observed G(x, f, T ) dependences for the films on the dielectric side of the insulator‐metal transition demonstrated the negative capacitance (NC) effect that was maximal for the nanocomposites with 0.40 <x< 0.60, where the metallic FeCoZr nanoparticles were totally oxidized. The NC effect was explained by a specially developed model for the ac hopping conductance of the electrons between the fully oxidized nanoparticles embedded in the PZT matrix. In accordance with the model, under the determined conditions the observed structure of nanocomposites led to an increase in the hopping electron mean lifetime on nanoparticles and hence to the possibility of positive angles of the phase shifts θ and a proper NC (inductive-like contribution) effect. (Some figures may appear in colour only in the online journal)

Inductive type properties of FeCoZr–CaF2 and FeCoZr–PZT nanocomposites

The paper presents investigations into frequency dependences of conductivity, capacitance and the phase angle θ for nanocomposites (FeCoZr)x(CaF2)(100−x) and (FeCoZr)x(PZT)(100−x). The nanocomposites have been produced with the application of ion-beam sputtering using pure argon ions (oxygen-free materials) and mixed ions of argon and oxygen (oxygen materials). The phase angle versus frequency characteristics for the oxygen nanocomposites show a transition from negative to positive phase angle values along with the frequency increase. The maximum observed phase angle θ values reach beyond the 90°. The phase angle transition through 0° is accompanied with the voltage resonance phenomenon that is represented by strong minima in the capacitance versus frequency curves. In the conductivity versus frequency characteristics, strong minima occur during the phase angle θ transition through 90°, which corresponds to the occurrence of current resonance. Occurrence of the coilless inductance features in nanocomposites (FeCoZr)x(PZT)(100−x) and (FeCoZr)x(CaF2)(100−x), produced with the ion-beam sputtering using argon and oxygen ions, is related to the formation of a subsurface layer of metal oxides on the metallic phase nanogranules.

Temperature and frequency dependences of real part of impedance in the FeCoZr-doped PZT nanogranular composites

The study of carrier transport in granular nanocomposite films consisting of ferromagnetic Fe45Co45Zr10 alloy nanoparticles embedded in a low-conductive Pb81Sr4(Na5Bi5)15(Zr57.5Ti42.5)O3 matrix has been performed. Real part of the impedance of the nanocomposites was studied as a function of composition, temperature and frequency, for the samples with 25 ≤ x ≤ 80 at.%, deposited by ion-beam sputtering in Ar + O2 gas mixture at the oxygen pressures of

An analysis of AC conductivity in moist oil-impregnated insulation pressboard

P_{O_2 }

Magnetic Anisotropy in Bicomponent Self-Assembled Ni and Ni-Pd Nanowires Studied by Magnetic Resonance Spectroscopy

= 2.4·10−3 and 3.7·10−3 Pa. It has been proved that approaching the threshold concentration, xC in the FeCoZr alloy resulted in the transition from high-ohmic to low-ohmic state with the x increase, without the change of hopping mechanism of carrier transport.

Capacitive properties of nanocomposite (FeCoZr)x(PZT)(100-x) produced by sputtering with the use of argon and oxygen ions beam

The paper presents research results of testing AC conductivity in a moist oilimpregnated electric insulation pressboard, depending on the moisture content level and temperature of the samples. A new method has been elaborated for converting experimentally obtained dependences from frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 /dpl deg/C). Activation energy values have been determined for the conduction and relaxation time. It has been found the conductivity is realized by electron tunnelling between potential well formed by water molecules contained in the structure of moist cellulose.

Comparison of the electrical properties of canola oil with commercially available mineral oil

Self-ordered arrays of Ni, Ni(50)Pd(50), and Ni(78)Pd(22) nanowires were synthesized by simultaneous electrochemical deposition of Ni and Pd components into porous templates of anodic aluminum oxide using alternating current. This paper is focused on the interplay of structure and chemical composition of Ni and Ni-Pd bicomponent nanowires arrays and the peculiarities of its magnetic anisotropy.

Statistical approach to endurance models - data processing using regression models

The paper established that, the hopping mechanism of the charge exchange for the (FeCoZr)64.4(PZT)35.6 nanocomposite and the additional polarization of tested sample occurs. As frequency increases two frequency areas where capacitance decreases can be observed. Correlation between the conductivity increase and the capacitance decrease has been observed for the both stages of their variability. Voltage resonance phenomenon for the studied material was observed. The zero crossing in the frequency dependence of phase difference transition is accompanied with this phenomenon, which is reflected by a sharp minimum in the capacitance versus frequency characteristics.

Low-Temperature DC Carrier Transport in (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x Nanocomposites Manufactured by Sputtering in Pure Ar Gas Atmosphere

Insulating liquids are used as electrical insulation and cooling medium for power transformers. The most commonly used insulation liquid is mineral oil. Mineral oil is characterized by its high flammability and poor biodegradability. On the other hand, this oil has very good electrical properties. The future development of biodegradable oil is most focused on vegetable oils. The disadvantage of this oil is faster aging process compared to mineral or synthetic oils. This paper discusses the experiment, which is divided into two parts. In both parts of the experiment are investigated mineral oil and canola oil. The first part of the experiment follows the dissipation factor, permittivity and resistivity. The second part follows the dielectric strength of these oils.

Analysis of AC conductivity in wet oil impregnated insulating paper

The paper presents a methodology for processing experimental data related to the issue of the electrical insulation system endurance, using the method of accelerated laboratory aging. Several possible approaches are proposed. Traditionally used is the phenomenological approach combined with mathematical regression of measured data. This method is complemented by confidence intervals to ensure statistical certainty of the results of the experiment statements. The paper also describes a statistical approach to endurance modeling, however similarly supplemented with statistical certainty by using confidence intervals. Statistical certainty based on confidence intervals brings very valuable information for the practical use of electrical insulation materials and systems, especially considering design and dimensioning.