V. P. Popov

Investigation into the Mechanism of Oxidation on the Surface of Lead Selenide Semiconductor Structures

The oxidation of lead selenide samples prepared in the form of ground powders, pressed pellets, polycrystalline films, and faceted crystals is investigated. All samples are produced from a lead selenide batch heat treated under dynamic vacuum. The bulk and surface structural and phase compositions of the samples upon oxidation in dry air at temperatures of 298–773 K are studied using electron microscopy, X-ray diffractometry, and Auger electron probe microanalysis. The dependence of the resistivity of polycrystalline films and pressed pellets is analyzed in the temperature range 298–498 K in dry air and argon. It is demonstrated that the specific features in the temperature dependences of the resistivity of oxidized PbSe samples can be associated with their microstructure and environmental conditions. It is revealed that the PbSeO3 phase is formed on the surface of all the PbSe samples starting from room temperature, whereas no phase transformations are observed in the bulk of samples.

Preparation and Properties of Ceramic Composites with Oxygen Ionic Conductivity in the ZrO 2 -CeO 2 -Al 2 O 3 and ZrO 2 -Sc 2 O 3 -Al 2 O 3 Systems

Powder precursors in the ZrO2-CeO2-Al2O3 and ZrO2-Sc2O3-Al2O3 systems are prepared by the sol-gel synthesis. It is revealed that the electrical conductivity of the sample doped with scandium oxide is higher than the electrical conductivity of the sample doped with cerium oxide despite the higher content of the nonconducting phase Al2O3 (corundum). The thermal expansion coefficients are determined for all the ceramic samples under investigation. It is established that the Al2O3 dopant affects the thermal expansion coefficient. The ceramic materials studied can be used as solid-electrolyte sensors.

Synthesis and investigation of magnesium chromium spinel

Magnesium chromium spinel nanopowders have been synthesized through cocrystallization. The formation and structural perfection of the MgCr2O4 crystalline phase have been investigated in the temperature range 500–1400°C. The average size of crystals of the MgCr2O4 phase has been determined at different temperatures. The influence of the temperature, porosity, and reducing medium on the electrical conductivity of the MgCr2O4 phase has been studied.

Nanocrystalline ceramics based on the ZrO2-HfO2-Y2O3 system

The formation of nanopowders of cubic solid solutions in the ZrO2–HfO2–Y2O3 system is investigated using the coprecipitation method. Conducting ceramic materials are prepared from the powders at 1450°C.

Synthesis and study of oxide and phosphor-silicate nanocomposites for the creation of new-generation supercapacitors

Using the methods of joint precipitation of hydroxides and joint crystallization of nitrate solutions, nanocrystalline ceramics have been synthesized on the basis of lanthanum and neodymium chromites and the two-phase composition (ZrO2)0.6(In2O3)0.4 with average grain sizes of 80–90 and 50–60 nm, respectively. Nanoceramics possess electrical conductivity from 10−2 to 10 S cm−1 in the temperature range 20–800°C. Ion-conducting membranes compatible with the obtained electrode ceramics have been synthesized by the sol-gel method from silica gels doped with orthophosphoric acid.

Oxidation of the zirconium boride-silicon nitride composite in the temperature range 1100–1300°C in air

Composite materials and coatings based on zirconium boride and silicon nitride have been prepared by heat treatment of mixtures of the initial components in air. The chemical reactions result in the formation of the glass melt encapsulating initial particles, which provides an increased heat resistance of the material. The kinetics of high-temperature oxidation of the composite based on the ZrB2-Si3N4 system has been studied. The interaction between solid components of the ZrB2-Si3N4 system, atmospheric oxygen, and the glass melt has been described in terms of the formal kinetic equations for heterogeneous processes. Thermogravimetric, thermal, and X-ray powder diffraction analyses have been carried out, and the electrical resistivity of the compact samples has been determined.

Porous conducting ceramic nanomaterials based on lanthanum and neodymium chromites

The nanopowders based on lanthanum and neodymium chromites are synthesized through cocrystallization. Ceramic materials with an open porosity of 37–42% are prepared. The influence of the reducing medium on the electrical conductivity is investigated at temperatures in the range 20–1300 °C. It is revealed that the introduction of nickel into the ceramic composite leads to an increase in the electrical conductivity.

Preparation of nanodisperse solid solutions based on ZrO2 and HfO2 from hydroperoxides

A procedure for preparing solid solutions based on zirconium and hafnium hydroperoxides is developed. This procedure is based on the coprecipitation of components in the presence of hydrogen peroxide. Amorphous nanopowders (Ssp = 80–90 m2/g, dmean = 2–3 nm) without any indication of the agglomeration of particles are synthesized. After the decomposition of complex hydroperoxides at a temperature of 500°C, the compacted powders undergo an active sintering at a temperature of 1450°C. The particle size after heat treatment does not exceed 50 nm. As follows from the electrical and physical characteristics obtained for these materials, they can be recommended for the use as solid electrolytes and sensors of oxygen partial pressure.

Neodymium nickelate—A cathode material for fuel cells

Nanocrystals of the neodymium nickelate (Nd2NiO4) compound have been synthesized using the method of the combined crystallization of nitrates’ solutions and its electrophysical properties have been investigated. It has been established that Nd2NiO4 is characterized with rather high specific conductivity of the metallic type (∼200 S cm–1) in the temperature range 500–900°C and the thermal expansion coefficient comparable with that of solid solutions based on ZrO2.

Synthesis of the study of solid solutions based on the ZrO2–HfO2–Y2O3(CeO2) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO2–HfO2–Y2O3(CeO2) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO2 and the physical–chemical properties of these ceramics are studied.