Using non-isothermal thermogravimetry (TG), the oxidation kinetics of oxygen-deficient lithium-titanium ferrospinel, Li0.649Fe1.598Ti0.5Zn0.2Mn0.051O4-d, manufac- tured by ceramic engineering is investigated. The oxidation annealing of powder samples is performed in air. Accord- ing to the X-ray phase analysis, the processes giving rise to variations in oxygen content occur within single-phase spinel structure. The experimental kinetic results are pro- cessed using the Netzsch Thermokinetics software. The oxidation rate constants and the effective coefficients of atmospheric oxygen diffusion into the ferrites are deter- mined. The effective activation energy E of oxygen dif- fusion is found to be 1.95 eV. It is demonstrated that an increase in the oxygen non-stoichiometry parameter d as a result of recovery annealing of ferrite powders in vacuum at T = 1,070 K for 2 h gives rise to a slight decrease in E down to 1.89 eV. The activation energy of oxygen grain- boundary diffusion is identified by the electroconduction method. The resulting value 1.93 eV is fairly consistent with that obtained by TG.

Investigation of oxidation processes in non-stoichiometric lithium–titanium ferrites using TG analysis

Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H–SiC. In configuration A, the deep level known as EH5 (Ea = EC − 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be TA → B > 730 K and for the opposite process TB → A ≈ 710 K. The energy needed to conduct the transformations were determined to be EA(A → B) = (2.1 ± 0.1) eV and EA(B → A) = (2.3 ± 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A → B and a charge carrier-emission dominated process in the case of B → A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.

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Capacitance transient study of a bistable deep level in e−-irradiated n-type 4H–SiC

The paper presents technical implementation of the electricalcapacitive method to perform in-process measurement of the capacitance per unit length of a single-core electric wire. The design of the electrocapacitive measuring transducer is proposed. The block diagram of the device CAP-10 developed to implement the proposed method is presented. The appearance of the device CAP-10 is showed, and its operating principle is described. It is shown that the change in water conductivity has a significant impact of the measurement result of the wire capacitance per unit length. The techniques to offset from the impact of water conductivity variation on measurement results are proposed. The technique of the device CAP-10 initial adjustment is proposed. It provides the desired function of the output signal transformation. The technique of the ‘operating’ adjustment to correct measurement results through systematic measurement error elimination is offered.

/pdf/capacitance-control-on-the-wire-production-line-3jjolbxx2t.pdf

Capacitance Control on the Wire Production Line

Adsorption properties of the polymer fibers are studied. It is shown that polypropylene fiber can be successfully applied for oil spill response for filtration purification of water from hydrocarbons. Polypropylene fibers from waste polymers have higher characteristics of adsorption capacity and degree of purification of water than commercially available fiber sipron.

Improvement of the Quality of Water Purification from Hydrocarbons Using the Fibers from Recycled Thermoplastics

https://robots.iopscience.iop.org/article/10.1088/1757-899X/289/1/012019/pdf

Influence of a high-power pulsed ion beam on the mechanical properties of corundum ceramics

It is shown that layer-by-layer measurements of the electron-transfer activation energy in polycrystalline ferrites allow the profiles of depth distribution of oxygen introduced from the atmosphere into a ferrite at the stage of sintering or thermal treatment to be studied using a simple experimental technique. The analytical equations proposed here make it possible to determine the volume and grain-boundary diffusion coefficients of oxygen using a minimum number of adjustable parameters.

Grain-boundary diffusion of oxygen in polycrystalline ferrites

For the first time a dielectric hysteresis is observed in a polycrystalline lithium-titanium ferrite in the temperature range 475–575 K. A thermal Barkhausen effect is detected during heating and cooling of ferrite specimens prepolarized in an electric field. The results provide evidence on the formation of properties similar to ferroelectric ones in lithium-titanium ferrites under certain conditions.

Anomalies of dielectric properties in a polycrystalline lithium-titanium ferrite

The temperature dependences of the real and imaginary parts of the complex dielectric permittivities of ceramic Li–Ti ferrospinel are measured within the frequency range 102–106 Hz. The empirical expressions describing these dependences are derived and the frequency-independent electrophysical parameters of the material under study are obtained. The best agreement between the experimental and calculation data is achieved when the time constant and the static dielectric permittivity are decreasing functions of frequency. A model of relaxational processes accounting for this result is proposed. A certain role in polarization of the relaxation agents, whose reorientation is controlled by tunneling electron transitions inside the “two-valence iron ion – three-valence metal ion”, is assumed. It is stated that under certain conditions, the relaxation agent reorientation is likely to possess a collective character. The temperature dependences e′ and e″ are derived for a number of dc currents at different electric field strengths. Sharp variations in the dielectric characteristics of the ceramics are found.

Dielectric Properties of Lithium–Titanium Ferrite Ceramics

Electric and magnetic properties of Li–Ti ferrite ceramics depending on sintering modes and controlled by the diffusion-based specimen-to-environment oxygen exchange are considered. The relationship between the properties of ceramics and the character of nonuniform distribution of oxygen in the bulk of a specimen is determined. A physical model of the processes giving rise to nonuniform distribution of oxygen in polycrystalline ferrite ceramics is proposed. The empirical dependences of specific conductivity on sintering time at 1373 K are obtained.

Nonuniform Distribution of Electric Properties in Ferrite Ceramics

Point defects in n-indium phosphide were studied by deep-level transient spectroscopy (DLTS). A radiation-induced bistable defect is found to form under irradiation of a space-charge region of n-InP Shottky-barrier diodes. The transformations of the defect configuration stimulated by heating, illumination, and current flow are studied.

V. V. Peshev

Papers

Grain-boundary diffusion of oxygen in polycrystalline ferrites

Anomalies of dielectric properties in a polycrystalline lithium-titanium ferrite

Dielectric Properties of Lithium–Titanium Ferrite Ceramics

Nonuniform Distribution of Electric Properties in Ferrite Ceramics

A bistable defect in InP