M. A. Kop’eva

Specifics of pyrohydrolytic and solid-phase syntheses of solid solutions in the (MgGa2O4)x(MgFe2O4)1 − x system

This work demonstrates the possibility of preparing solid solutions in the (MgGa2O4)x(MgFe2O4)1 − x system by pyrohydrolytic and solid-phase methods. It is shown that the products obtained have different specific surface areas depending on the ratio between metal nitrates and citric acid. The composition dependence of the unit cell parameter deviates considerably from the Vegard’s rule. The compounds obtained are found to be stable up to 300°C, which makes them candidate materials for electronics.

Crystallization of Mg(Fe 0.8 Ga 0.2 ) 2 O 4 - δ Films on Silicon with SiO 2 and TiO 2 Buffer Layers

The results of analysis of conceivable interactions between film and substrate materials during crystallization of Mg(Fe0.8Ga0.2)2O4-δ films with SiO2 and TiO2 buffer layers on silicon are reported. The calculated data are compared with the physicochemical parameters of Mg(Fe0.8Ga0.2)2O4-δ/Si, Mg(Fe0.8Ga0.2)2O4-δ/TiO2/Si, and Mg(Fe0.8Ga0.2)2O4-δ/SiO2/Si film heterostructures.

Subsolidus phase relations of Mg-Ga-Fe-O spinel solid solutions

The phase relations of Mg-Ga-Fe-O spinel solid solutions have been analyzed in a topological approach using composition diagrams. Oxides with the nominal compositions Mg1 − xGa2 − 2xFe3xO4 + δ and Mg1 − xGa2xFe2 − xO4 + δ (with x varied in steps of 0.1) prepared by a pyrohydrolytic process and air-annealed at 1270 K have been studied by X-ray diffraction.

Features of Mg(Fe0.8Ga0.2)2O4 synthesis by glycine-nitrate method

A finely dispersed powder of composition Mg(Fe0.8Ga0.2)2O4 was prepared by glycine-nitrate method. The use of glycine as a reducing agent allows preparation of the product without carbon-containing admixtures with unimodal particle size distribution and lower crystallization temperature (as compared with nitrate-citrate method of Mg(Fe0.8Ga0.2)2O4 synthesis) immediately after reaction completion.

Study of the process of the formation of Mg(Fe0.8Ga0.2)2O4 − δ films on Si

Conditions of the synthesis of magnetic semiconductor films of composition Mg(Fe0.8Ga0.2)2O4−δ on silicon have been optimized. As the barrier layer, which prevents the interaction between the film and the substrate during high-temperature crystallization of the films, a film of nanosized silicon dioxide was used. This, together with a high homogeneity of the composition of the target, allowed us to obtain Mg(Fe0.8Ga0.2)2O4−δ films on silicon characterized by the saturation magnetization (37 A m2/kg) that noticeably exceeds that for the volumetric analog (28 A m2/kg).

MgAl0.4Fe1.6O4 powders prepared via gel combustion

Powdered ferrite of composition MgAl0.4Fe1.6O4 is prepared by the combustion of gels consisting of a mixture of magnesium, aluminum, and iron nitrates, citric acid, and NH4NO3 added into the reaction mixture. The process is demonstrated to involve a single stage without the formation of volatile carbon-containing compounds when the ratio of the number of NH4NO3 moles to the total number of metal nitrate moles n = 10.1.

Gel decomposition and formation of MgFe1.6Ga0.4О4 powders

The thermal behavior of the gels that are formed in the synthesis of MgFe1.6Ga0.4О4 powders was studied by differential scanning calorimetry and thermogravimetry (DSC–TG). The combustion temperatures of the gels in flowing air and flowing argon were determined from experimental data and thermodynamic calculations. The calculations of combustion temperatures from the heat flow of reaction versus time are shown to be a reliable tool to determine the parameters of gel combustion.

Gel formation specifics in the synthesis of Mg(Fe0.8Ga0.2)2O4 by the glycine–nitrate method

The gel formed in the synthesis of Mg(Fe0.8Ga0.2)2O4 powder from corresponding metal nitrates and glycine was studied by thermal and IR spectral analyses. Being a bidentate ligand, glycine was established to initiate the gel combustion reaction resulting in the oxide of the above composition. Based on the data on ΔH298° and Cp of the reagents and reaction products, the thermodynamic parameters of this process were calculated.

Decomposition of aluminum oxynitride compounds in an air-vapor medium at 950°C

Aluminum oxynitride hydrolysis in wet air at a temperature of 950°C has been shown to lead to the formation of a phase whose composition lies beyond the Al2O3-AlN join in the Al-O-N system.

Synthesis of MgFe 1.6 Ga 0.4 O 4 by Gel Combustion Using Glycine and Hexamethylenetetramine

A powderlike material of composition MgFe1.6Ga0.4O4 was synthesized by gel combustion using a glycine–hexamethylenetetramine mixture. The gel produced by the synthesis was studied by thermal analysis (TGA/DSC) and IR spectroscopy. This mixture was shown to be efficient for obtaining homogeneous nanosized MgFe1.6Ga0.4O4. The morphology of the powders was characterized by scanning electron microscopy and X-ray powder diffraction analysis.