P. A. Tikhonov

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.

Oxidation Kinetics of Lead Selenide

The oxidation of lead selenide structures prepared in the form of powdered samples is investigated. The powders are produced from a lead selenide batch heat treated under dynamic vacuum and ground in an agate mortar. The mean grain size is equal to 0.5–3.0 μm. The thermodynamic analysis of the possibility of the main chemical reactions proceeding during the oxidation of lead selenide in an oxygen atmosphere is performed. The bulk and surface structural (and phase) compositions of the powdered samples upon oxidation in dry air at a temperature of 823 K for oxidation times of 5–240 min are studied using X-ray diffractometry. The analysis of the X-ray diffraction patterns shows that the PbSeO3 phase is formed on the grain surface of all PbSe powders, whereas no phase transformations are observed inside the grains. The charge state of Se atoms in PbSe crystallites oxidized to different states is determined from the chemical shifts of the K X-ray emission lines. The oxidation kinetics of lead selenide is examined at a temperature of 823 K. It is demonstrated that the kinetic dependences of the oxidation of lead selenide that are determined by two independent methods (chemical shift, X-ray diffractometry) are in satisfactory agreement with each other.

Electron Microscopic Investigation of the Structure of Gas-Sensitive Nanocomposites Prepared by the Hydropyrolytic Method

Polycrystalline films in the SnO2–In2O3 and SnO2–ZnO systems, which are of interest for use in gas-sensitive sensors, are grown from metal chlorides on a 22-XC ceramic substrate by the hydropyrolytic method. The nanocomposites based on tin dioxide are studied. The structure of polycrystalline grains is investigated by electron spectroscopy and X-ray diffractometry. The distribution of components in the samples prepared is examined using electron probe X-ray microanalysis. It is established that homogeneous films in the SnO2–In2O3 system up to 10 mol % In2O3 in the initial solution can be grown by the hydropyrolytic method.

Temperature Dependence of the Resistivity for Metal-Oxide Semiconductors Based on Tin Dioxide

Polycrystalline films of SnO2 and films in the SnO2–In2O3 and SnO2–ZnO systems, which are of interest for use in gas-sensitive sensors, are grown from metal chlorides on a 22-XC ceramic substrate by the hydropyrolytic method. The dependences of the resistivity for metal oxide films based on tin dioxide are measured in the temperature range 200–400°C. The distribution of phases in the samples prepared is examined using electron probe X-ray microanalysis. It is shown that the specific features in the temperature dependences of the resistivity for the semiconducting metal-oxide films grown can be associated with their microstructure and the environmental condition. The temperature dependences of the resistivity for all the metal-oxide films studied exhibit a semiconductive behavior.

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.

Physicochemical properties of nanocrystalline composites based on ZrO2, Al2O3, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO2-Al2O3-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO2, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.

Investigation of some physicochemical properties of ceramics, single crystals, and nanofilms based on zirconia, hafnia, and rare-earth oxides

Precursor powders in the ZrO2-CeO2-Sc2O3-Al2O3 system have been prepared using the sol-gel method. A physicochemical analysis of the synthesized ceramics, single crystals, and nanofilms based on ZrO2 and HfO2 oxides has been performed. It has been revealed that the introduction of alumina Al2O3 into the ZrO2-based ceramic samples reduces the thermal expansion coefficient and that these ceramic materials possess a high electrical conductivity as compared to the other materials under investigation.

Investigation of the products of oxidation of lead selenide by IR spectroscopy

The optical properties of lead selenide powders are investigated by Fourier-transform IR spectroscopy at room temperature, as well as at temperatures of 500 and 550°C. The diffuse reflection spectra of the initial and heated powders of the PbSe compound are measured. It is revealed for the first time that the surface of the initial and heated samples of the PbSe compound contains a layer of amorphous biselenite Pb(HSeO3)2 · n H2O. This makes it possible to explain the previously observed local minimum at temperatures close to 100°C in the temperature dependence of the electrical resistivity of the powders.

Ceramic nanocomposites based on oxides of transition metals for ionistors

Low-temperature synthesis methods are used to produce nanoceramic materials for electrodes of the following ionistors: (ZrO2)0.6(In2O3)0.4, praseodymium cobaltite, as well as neodymium, lanthanum, and nickel chromites; they operate in the presence of an ion-conducting phosphorosilicate separator membrane and phosphate impregnation. Film electrodes of ionistors are fabricated that consist of nanocrystalline oxide materials deposited as a thin film on a porous electroconductive metal substrate, i.e., foamed nickel. The MnO2-foamed nickel electrode has a specific capacity of 45.0 F g−1, which is compared with that of industrial supercapacitors.

Synthesis and study of sensor oxide nanofilms in a ZrO2-CeO2 system

Methods of the synthesis of nanostructured oxide films have been suggested for gas sensors based on zirconium and cerium dioxides with a cubic structure and crystallite size of 10–12 nm. The compositions in the CeO2-ZrO2 system having the highest sensitivity have been predicted, based on quantum-chemical calculations via the density functional method (DFT). These calculated data are correlated to the experimental results of the measurement of electroconductivity on air and in a reducing medium (CO2 + CO). The obtained nanosized oxide films have a high response time (5–6 s) and sensitivity; they are promising as resistive sensors for the detection of media with reduced oxygen content. The method of computer simulation allows the reduction of the search period of new materials for gas sensors.