Search

Using a highly sensitive torsional vibration technique, the authors have determined the critical temperatures of the superconducting transition (Tc) of individual phases of multiphase cuprates [Bi1.7Pb0.3Sr2Ca(n-1)CunOy (n = 2–30)] in a constant external magnetic field (H) in the temperature range of 77 to 270 K. It has been found that oscillation damping peaks are more pronounced when a sample is rapidly cooled in an external magnetic field (FC) to a temperature of 77 K and then is slowly warmed to room temperature. An increase in the time of sample exposure to a magnetic field at 77 K leads to a rise in the temperature Tc of different phases, and to an increase in the intensity of a signal corresponding to high-temperature phases with Tc > 240 K. Structural studies have shown that with increasing sample exposure time at 77 K, as a result of sample compression an increase in stress concentration at grain boundaries appears to increase defect density and to enhance the pinning of Abrikosov vortices, i.e. creates new (additional) conditions for their “freezing” during the field cooling (FC) procedure. It has been established that in samples of the Bi1.7Pb0.3Sr2Ca(n-1)CunOy (n = 2–30) series, the critical temperature Tc increases from 107 K to ≥ 240 K with an increase in n.

The electrophysical properties of semiconductor–superconductor sandwich pairs (InP–Bi/Pb 2223, 2234, 2245) are investigated, in which homophase superconductors based on bismuth cuprates with high reproducible critical temperatures of superconducting transition Tc = 107–180 K are used. The advantage of melt solar technology for obtaining superconducting materials is demonstrated. The microstructure and phase composition of strongly anisotropic superconductors with nominal composition Bi1.7Pb0.3Sr2Ca(n– 1)CunOy (n = 3, 4, 5) are researched. A technique of experimental determination of superconducting transition critical temperatures Tc in single-phase and homophase HTSC samples is presented. The current–voltage characteristics of InP–Bi/Pb pairs are investigated. The relationship between the electrical resistance of sandwich pairs and superconductor critical temperature Tc is established.

An opportunity of using solar energy to develop a multicomponent ceramic material synthesis technology using melts has been demonstrated. Optical and energy parameters of the 1 MW Large solar furnace for synthesizing aluminum titanate-based materials are presented along with their phase and grain size compositions depending on the melt cooling rate. A possibility of obtaining a two-phase material containing the tialite phase and spinel is shown. A positive effect of the spinel phase on the properties of ceramics made from the material synthesized by using solar energy has been established.

The phase composition and superconducting properties of high-temperature superconductors of homologous series of Bi1.7Pb0.3Sr2Ca n − 1Cu n O y (n = 4−9) based on amorphous precursors obtained under the influence of solar energy was studied. The formation of structural defects was established, and their relation with the increase in the temperature of the superconducting transition up to 181 K was assumed.

The problem of energy shortage governs the search for renewable energy sources. Solar energy is used to synthesize and study the properties of the following oxide compounds: REE titanates (La–Lu), titanates of the pseudo-brookite type, solid solutions of the fluorite type based on ZrO2 and HfO2, and superconductors of theseries Bi1.7Pb0.3Sr2Ca n–1Cu n O y (n = 2 – 20). The advantages of synthesis technology using solar energy and a favorable change in ceramic functional material properties is demonstrated.

The phase composition of composite ceramic based on aluminum titanate and additives synthesized by concentrated solar radiation by means of solid phase reactions and by the induction method is investigated. It is revealed that the additives positively influence the sample’s mechanical properties.

The mechanical properties of an aluminum titanate-based ceramic are increased by decreasing the grain growth kinetic of the initial material, which is synthesized by melting in a solar furnace. The thermomechanical properties are improved if the following additives are introduced: mullite, spinel, and a eutectic of Al2O3-ZrO2.

Investigated is the possibility of synthesis of cubic silicon carbide from silica earth minerals (quartzite and quartz sand) by exposure to intense solar radiation. The influence of the intensity of the solar radiation flux on the silicon carbide formation process is studied in detail.

The properties in isostructural and isostoichiometric series of monotitanates and dititanates of the rare earth elements (REE), titanates with structure of pseudobrookite type, and solid solutions with fluorite structure based on ZrO2 and HfO2 are investigated. The differences determined by molten phase synthesis via the action of concentrated solar radiation are shown. It is proposed that ozone and excited valence electrons, i.e., the factors caused by concentrated solar radiation, influence the phase composition and properties of these oxide compounds.

The properties of the spherulites based on aluminum oxide, mullite, and zirconium dioxide that are obtained by melting and subsequent quenching in a 1000 kW solar furnace are studied. These spherulites are hollow. The thickness of the wall of the sphere is determined by the quenching rate. The microstructure of the spherulites that are based on aluminum oxide consists of crystallites of cubic form, the microstructure of the spherulites that are based on zirconium dioxide consists of micrograins of rounded form. The hardness and the elastic properties exceed the known values for the electrically melted materials that are based on corundum and zirconium dioxide.

We studied the influence of the form and amount of stabilizer and the synthesis schedules on the phase ratios in the approximate eutectic compositions for the systems ZrO2-Al2O3 (MgAl2O4, SiO2, mullite), and also the thermodynamic stability and mechanical properties of the ceramics based on them.

En vue de mieux comprendre les effets de la microstructure, on etudie l'influence de la grosseur de grain et de la disposition relative des grains sur la stabilite thermodynamique de ceramiques de titanate d'aluminium.