Carbon-coated nanocrystalline MgO samples were prepared by butadiene pyrolysis at 500 °C over aerogelprepared MgO samples. Samples with carbon loadings of 1.2, 3.2, 5.0, 10.0, and 15.9 wt % were prepared. Initial carbon formation rate was about 2 wt % per hour. According to HRTEM, the structure of the mineral component in the carbon-mineral materials was not altered by the carbon deposition. At low loading of carbon, it was found to deposit only inside the MgO aggregates 5-10 nm from their outside surface, forming thin individual bands 1.5-2 nm long. At the highest loading, carbon deposits form three-dimensional graphitelike multilayer structures filling the pore volume of the MgO aggregates and cover the outside surface of the aggregates with a thin monolayer coating. A single symmetric Lorentzian line with g ) 2.0029 attributable to carbon deposits has been observed in the ESR spectra of the carbon-mineral materials. It gradually narrows from 5.0 to 1.9 G as the carbon loading increases from 1.2 to 15.9 wt %. Nitroxyl radicals formed after dinitrobenzene adsorption on MgO nanocrystals have been used as a spin probe for estimation of the concentration of strong basic sites present on the surface of the carbon-mineral materials and degree of their coverage with carbon. The sample with the carbon loading of 15.9 wt % has practically all such sites blocked with carbon, while samples with carbon concentration between 5 and 10 wt % seem to be the most promising candidates for practical application as destructive adsorbents.

This article demonstrates the possibility of creating memory devices based on polycrystalline mayenite. In the course of the study, structural characterization (XRD, TEM) of ceramic samples of mayenite was carried out, as well as a study of the spectral (THz range) and electrophysical characteristics. Materials obtained by calcination at high (1360–1450 °C) temperatures in an inert argon atmosphere differ in the degree of substitution of oxygen anions О2− for electrons, as indicated by the data on the unit cell parameters and dielectric constant coefficients in the range of 0.2–1.3 THz, as well as differences in the conducting properties of the samples under study by more than five orders of magnitude, from the state of the dielectric for C12A7:O2− to the conducting (metal-like) material in the state of the C12A7:e− electride. Measurements of the current–voltage characteristics of ceramic C12A7:e− showed the presence of memristive states previously detected by other authors only in the case of single crystals. The study of the stability of switching between states in terms of resistance showed that the values of currents for states with high and low resistance remain constant up to 180 switching cycles, which is two times higher than the known literature data on the stability of similar prototypes of devices. It is shown that such samples can operate in a switch mode with nonlinear resistance in the range of applied voltages from –1.3 to +1.3 V.

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We studied the formation process of a mayenite structure from hydroxide precursors in different gas media. According to X-ray diffraction data, this method allows a well-crystallized mayenite (Ca12Al14O33 or C12A7) phase to be obtained at low (500–900 °C) temperatures with an insignificant impurity of CaO. It was shown that the lattice parameters for C12A7 obtained in an inert atmosphere (Ar) were lower when compared with similar samples in the air. These results can be explained by the different levels of oxygen nonstoichiometry in the resulting phase. We noted that sintering and crystallization of mayenite proceeds at lower temperatures in Ar than in the air medium. We found the presence of donor and acceptor active sites on the surface of mayenite, which was detected by the spin probe method. The specific (per unit surface) concentration of such sites (2.5 × 1016 m−2 and 1.5 × 1015 m−2 for donor and acceptor sites, respectively) is comparable to that of γ-Al2O3, which is traditionally used as catalyst support. This allows it to be used in adsorption and catalytic technologies, taking into account its high specific surface area (~30–50 m2/g at a low synthesis temperature).