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Nanocrystalline cobalt oxide Co3O4 has been prepared by precipitation and subsequent thermal decomposition of a carbonate precursor, and has been characterized in detail using XRD, transmission electron microscopy, and FTIR spectroscopy. The sensory characteristics of the material towards carbon monoxide in the concentration range 6.7–20 ppm have been examined in both dry and humid air. A sensor signal is achieved in dry air at sufficiently low temperatures T = 80–120 °C, but the increase in relative humidity results in the disappearance of sensor signal in this temperature range. At temperatures above 200 °C the inversion of the sensor signal in dry air was observed. In the temperature interval 180–200 °C the sensor signal toward CO is nearly the same at 0, 20 and 60% r.h. The obtained results are discussed in relation with the specific features of the adsorption of CO, oxygen, and water molecules on the surface of Co3O4. The independence of the sensor signal from the air humidity combined with a sufficiently short response time at a moderate operating temperature makes Co3O4 a very promising material for CO detection in conditions of variable humidity.

Cobalt oxide based nanostructures are perspective materials for gas sensors, photocatalysts, and other devices for ecology applications due to the high concentration of chemisorbed oxygen and catalytic activity in oxidation reactions. Finely dispersed nanocrystalline oxides Zn x Co3–x O4 (0 ≤ x ≤ 1) with a high level of conductivity have been synthesized by the chemical precipitation of oxalates with subsequent thermal treatment. Comprehensive studies of the morphology, electrophysical properties, nature and concentration of defects in the obtained materials were carried out. It is shown that the introduction of zinc atoms to the Co3O4 structure leads to a sharp increase in conductivity by more than 5 orders of magnitude. In addition, the zinc-induced interplay of Co2+ spin centers between tetrahedral and octahedral sites was revealed using the EPR method. The correlation between the conductivity and the concentration of Co2+ ions in tetrahedral and octahedral environments was established for the first time. The obtained results open up the possibility of fine-tuning the electronic properties of nanostructured Zn x Co3–x O4 by variation of zinc concentration in the samples.

Resistive and capacitive switching in capacitor metal/nanocomposite/metal structures based on (CoFeB) x (LiNbO 3 ) 100−x nanocomposite (NC) fabricated by ion-beam sputtering with metal content x  8-20 at. % is studied. The peculiarity of the structure synthesis was the use of increased oxygen content ( 210 −5 Torr) at the initial stage of the NC growth. The NC films, along with metal nanogranules of 3-7 nm in size, contained a large number of dispersed Co (Fe) atoms (up to ~10 22 cm -3 ). Measurements were performed both in DC and AC (frequency range 5-13 MHz) regimes. When switching structures from high-resistance (R off ) to low-resistance (R on ) state, the effect of a strong increase in their capacity was found, which reaches 8 times at x  15 at. % and the resistance ratio R off /R on  40. The effect is explained by the synergetic combination of the multifilamentary character of resistive switching and structural features of the samples associated, in particular, with the formation of high-resistance and strongly polarizable LiNbO 3 layer near the bottom electrode of the structures.

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