Alumina - 7.5 wt% yttria-stabilized zirconia (YSZ) ceramic composites were sintered using 24 GHz microwave heating at rates of 10 - 200 degrees C/min with zero isothermal hold. The starting powders were nanophase i-Al2O3 and YSZ prepared by a laser evaporation method. The final densities of the sintered samples were up to 97.5 % of the theoretical value. The samples exhibited rapid densification until transformation to the alpha-Al2O3 phase. The temperature of the densification rate peak (and hence of the phase transformation) decreased consistently with increasing microwave electromagnetic field intensity (varied by using different susceptor materials). The densification peak temperature difference between microwave and conventional sintering experiments exceeded 200 degrees C.

The superconducting sigma neuron is a single-junction interferometer, with a part of the circuit shunted by an additional inductance, which is also used to generate the output signal. It was previously predicted that the transfer function of this device would be close to the sigmoidal one at a certain relation between the values of inductance of its parts. This interferometer can be fabricated as a multilayer thin-film structure over a superconducting screen, which allows measuring the output magnetic flux in a single element. An analysis of the experimental data showed that the use of a superconducting screen did not ensure complete independence of the sigma neuron elements, as was assumed in the theoretical model. This paper presents a generalized model of the stationary state of a sigma neuron that takes into account the interaction between all its parts, including the input and readout elements.

A step-by-step description of the technique for manufacturing various van der Waals heterostructures is provided. First, the procedure to obtain monolayer and few-layer flakes from layered materials, in particular graphite and hexagonal boron nitride, is discussed. Next, different approaches to their assembly depending on the required final structure are considered. Finally, the procedure for making ohmic contacts is described in detail and the parameters for plasma chemistry and metal deposition are given. The field effect is discovered in transport measurements carried out at various temperatures, but a number of features, such as a strong shift of the charge neutral point from the zero-gate voltage, a large resistance away from the charge neutral point, and a low mobility, indicate a poor quality of the resulting devices. Nevertheless, one of the fabricated devices demonstrates good quality: the maximum mobility is estimated as 15 000 cm2/(V s), and the magnetic field dependences demonstrate the quantum Hall effect that is standard for high-quality graphene. Unexpectedly, scanning electron microscope images of the resulting devices reveal a large amount of contamination on the surface of the flakes, which may explain the corresponding quality of our devices. Preliminary results of flakes cleaning with chemical compounds and thermal treatment are presented.

Samples of alumina - 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 degrees C/min and zero hold time. The final relative density was 96-99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98-99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm(3) resulted in a shift of the shrinkage curves by about 100( degrees )C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m (1/2) .

The transport properties of niobium films and strips fabricated on Y3Fe5O12 single-crystal films with the (111) and (100) orientations are studied in a wide temperature range from 300 to 4 K. It is shown that a decrease in the temperature of the superconducting transition and its broadening are more significant for the (111) orientation of the films, despite the fact that numerous magnetic-domain walls are localized under the niobium strips and should enhance superconductivity. It is shown that the dependence of the niobium resistance on the direction of magnetization and current is observed only in narrow and thin niobium strips and disappears as they thicken. Rotation of the in-plane magnetic field makes it possible to effectively switch the resistance of such structures in the region of an extended superconducting transition. A scheme for creating a diode effect on niobium strips is proposed and implemented.

The voltage–current characteristics of planar Pd0.99Fe0.01–Nb–Pd0.99Fe0.01 microbridges at temperatures significantly lower than the critical one are studied experimentally. It has been found that a magnetic memory effect, which is manifested in the dependence of the shape of the voltage–current characteristics on the mutual orientation of the magnetizations of the F layers, is observed even at such low temperatures. It has been shown that the studied sample can serve as a magnetic switch with a voltage distinction of more than 600 μV, which corresponds to a characteristic frequency of about 300 GHz if such bridges are used as memory elements in rapid single-flux quantum logic devices. These characteristics are obtained at a temperature of 0.93Tc, which is the minimum operating temperature of the implemented memory element. A low-voltage mode of operation of the sample is discovered, characterized by a wide range of permissible bias currents.

The artificial neuron proposed earlier for use in superconducting neural networks is experimentally studied. The fabricated sample is a single-junction interferometer, part of the circuit of which is shunted by an additional inductance, which is also used to generate an output signal. A technological process has been developed and tested to fabricate a neuron in the form of a multilayer thin-film structure over a thick superconducting screen. The transfer function of the fabricated sample, which contains sigmoid and linear components, is experimentally measured. A theoretical model is developed to describe the relation between input and output signals in a practical superconducting neuron. The derived equations are shown to approximate experimental curves at a high level of accuracy. The linear component of the transfer function is shown to be related to the direct transmission of an input signal to a measuring circuit. Possible ways for improving the design of the sigma neuron are considered.

The transfer function of a shunted two-junction interferometer, which was previously proposed as a basic element of superconducting neural networks based on radial basis functions, has been measured for the first time. The sample has been implemented in the form of a multilayer thin-film structure over a thick superconducting screen with the inductive supply of an input signal and the readout of an output signal. It has been found that the transfer function is the sum of the linear and periodic bell-shaped components. The linear component is likely due to the direct transfer of the input magnetic flux to the measuring circuit. The shape of the nonlinear component, which is the output signal of a Gauss neuron, can be approximately described by a Gaussian distribution function or, more precisely, by a parametric dependence derived theoretically in previous works. It has been shown that the transfer function of the Gauss neuron can depend on the choice of the working point of the measuring circuit, which promotes the development of integrated neural networks based on implemented elements.

A method for preparation of dense Y2O3-MgO composite ceramics by the microwave sintering was developed. The initial powders were obtained by glycine-nitrate self-propagating high-temperature synthesis (SHS) with different oxidant-to-fuel ratio. Density and IR-transmission of microwave sintered Y2O3-MgO ceramics increase with respect to dispersity of the SHS-powders and reach its maximum values for the powder prepared in a 20% fuel excess. The sintering behavior of Y2O3-MgO compacts was investigated by optical dilatometry and measuring an electric conductivity upon heating. Significant microwave radiation power surges at temperatures of 900-1000 degrees C, caused by the decomposition of magnesium carbonate, have been found. As a result of matching the conditions for the synthesis of powders and sintering modes, a transmission of composite ceramics of 78% at a wavelength of 6 mu m was achieved at a maximum processing temperature of 1500 degrees C.

Using the method of sintering by microwave heating at a rate of 10–100°C/min to a temperature of 1250 °C without isothermal hold, we obtain ceramic samples with the composition Ba0.75Sr0.25TiO3. The experiments are performed on a gyrotron complex for the high-temperature microwave treatment of materials, which is operated at a frequency of 24 GHz with a maximum power of 5 kW. The features of the formation of a solid solution in the sintered samples are analyzed. The dependence of the intensity of recrystallization growth of grains on the microwave-heating rate during the sintering is demonstrated. The permittivity of the samples obtained by microwave sintering with heating rates of 10 and 30 °C/min amount to 3600–4400 in the frequency range 25Hz–3MHz at room temperature.

The transfer function of a shunted two-junction interferometer, which was previously proposed as a basic element of superconducting neural networks based on radial basis functions, has been measured for the first time. The sample has been implemented in the form of a multilayer thin-film structure over a thick superconducting screen with the inductive supply of an input signal and the readout of an output signal. It has been found that the transfer function is the sum of the linear and periodic bell-shaped components. The linear component is likely due to the direct transfer of the input magnetic flux to the measuring circuit. The shape of the nonlinear component, which is the output signal of a Gauss neuron, can be approximately described by a Gaussian distribution function or, more precisely, by a parametric dependence derived theoretically in previous works. It has been shown that the transfer function of the Gauss neuron can depend on the choice of the working point of the measuring circuit, which promotes the development of integrated neural networks based on implemented elements.

Nonequilibrium phenomena in planar Josephson SNS nanostructures, where the superconductor (S) is Nb and the normal metal (N) is Cu or Au, have been studied experimentally. Using additional N electrodes attached to the S banks of the Josephson SNS junction, transport measurements have been performed at low temperatures with the injection of quasiparticles with the use of local and nonlocal connection schemes. The charge-imbalance relaxation length in niobium at temperatures much lower than the superconducting transition temperature has been determined experimentally for the first time.

Rapid microwave sintering processes with heating rates of up to 300 degrees C/min and zero isothermal hold have been implemented using a 5 kW 24 GHz gyrotron system for high-temperature microwave processing of materials. ZnO-based varistor ceramics, BaTiO3/SrTiO3 dielectric ceramics and Gd:CeO2 ceramics for solid electrolyte applications have been sintered to densities of up to 96% of the theoretical value. Using in situ optical dilatometry, correlation between the development of thermal instability under intense volumetric microwave heating and the early onset of densification has been revealed. The influence of the absorbed microwave power on densification and grain growth has been studied by comparing direct and susceptor-assisted microwave heating processes. The possibility of tailoring the microstructure and functional properties of the obtained materials by choosing optimal regimes of rapid microwave sintering is discussed.

Gd:CeO2 ceramic samples with a density of up to 96% of the theoretical value have been obtained by rapid 24 GHz microwave sintering with heating rates of up to 300 degrees C/min and zero hold time. It has been found that a higher absorbed microwave power density lowers the densification onset temperature by up to 150 degrees C. The grain size in the final materials decreased with an increase in the heating rate at a lower power density (a few W/cm(3)) but increased at a higher power density (similar to 40 W/cm(3)). The ionic conductivity of the sintered materials depended on the microwave heating rate; samples sintered at 30 - 100 degrees C/min had an ionic conductivity of approximately 0.5 S/m at a temperature of 560 degrees C.

The transport properties of niobium films and strips fabricated on Y3Fe5O12 single-crystal films with the (111) and (100) orientations are studied in a wide temperature range from 300 to 4 K. It is shown that a decrease in the temperature of the superconducting transition and its broadening are more significant for the (111) orientation of the films, despite the fact that numerous magnetic-domain walls are localized under the niobium strips and should enhance superconductivity. It is shown that the dependence of the niobium resistance on the direction of magnetization and current is observed only in narrow and thin niobium strips and disappears as they thicken. Rotation of the in-plane magnetic field makes it possible to effectively switch the resistance of such structures in the region of an extended superconducting transition. A scheme for creating a diode effect on niobium strips is proposed and implemented.

The magnetoresistance of a planar microbridge based on a three layer Pd0.99Fe0.01–Nb–Pd0.99Fe0.01 FSF sandwich near its superconducting transition is studied. We previously showed that the magnetoresistance curve of such samples is hysteretic and contains dips (negative peaks of the resistance) in the coercive fields. In this work, it is found that the low-resistance state has a memory effect. Functioning of such a sample as a superconducting memory element is demonstrated. The effect of the ferromagnetic Pd0.99Fe0.01 layer on the superconducting transition temperature of the proposed memory element is studied by measuring the dep-endence of the critical temperature of bilayer Pd0.99Fe0.01–Nb FS structures on the thickness of the Pd0.99Fe0.01 layer.

24 GHz microwave sintering of BaTiO3 ceramics has been studied under rapid heating at a rate of up to 300 degrees C/min to a maximum temperature of 1150-1300 degrees C with no isothermal hold. Under direct volumetric microwave heating the temperature difference measured between the center and periphery of the samples was 200-300 degrees C, and the estimated volumetrically absorbed power density was about 40 W/cm(3). The use of a SiC susceptor made it possible to reduce the required microwave power and equalize the temperature distribution, but in this case densification started at a higher temperature. Evidence of recrystallization-induced microstructure transformation propagating outward from the core of the sample is presented. The possiblity of implementing control over the microstructure and functional properties by choosing the parameters of the microwave sintering regime is discussed.