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Sr2FeMoO6–δ single-phase samples without Fe/Mo cations superstructural ordering (P) and with Curie temperature 407 K were obtained by the solid-phase technique. According to the XRD data, the growth dynamics of the parameter P is nonlinear. In this case, the process of reaching maximum values of P (Pmax) is long and its rate is several times lower than the change of the oxygen index 6–δ. It was found that with increasing temperature of isothermal annealing, P increases and reaches maximal values 88 % at T = 1320 K for 120 h, Pmax = 92 % at T = 1420 K for 100 h, while Pmax = 90 % at T = 1470 K for 45 h. One can assume that the lower values of Pmax at T = 1470 K than at T = 1420 K are due to the influence of thermal energy on the destruction of chain ordering of Fe and Mo cations placed in staggered order. Based on the analysis of P time dependences, two relaxation processes can be found and the dP/dt = ¦(t) can be divided into two regions – I and II. In the region I the relaxation time is shorter than that in the region II. The point is that the ordering of cations in the –O–Fe–O–Mo–O chains in the region I requires atomic displacements by approximately one interatomic distance, whereas in the region II cation displacements occur over long distances with the formation of long[1]chain long-range ordering.

The present paper is devoted to the study of the structural degradation mechanisms of ferroelectric having Pb1−хBaхZr0,53Ti0,47O3−δ composition. On the base of investigations of the influence of temperature-time synthesis modes on the structural perfection degree of the Pb0,85Ba0,25Zr0,53Ti0,47O3−8 compound, it has been determined, that a shift of the position of the XRD reflex from the plane (112) and its broadening, which is caused by the amorphization and an increase of the elastic stresses in the material crystal lattice during the annealing of the compound. It has been demonstrated that at the increase of the annealing temperature up to 520 K, the crystal lattice of the ferroelectric is deformed by means of a formation of VPb,V0 and [V О •• 2Pb / i ] defects, which is realized in a decrease of the I(hkl) intensity relationship of the XRD reflexes from the planes (112) and (211). It has been supposed that an excess of lead is produced on the grain boundaries as a result of this annealing process, which promotes a local manifestation of the liquid phase. This phase which takes place in the transfer of the material components, not only increases the interaction of the reacting components, but lowers the stability of their crystal lattices due to the formation of point defects, as well. In this case, the lattice state is determined both by the emergence of the oxygen (VО) and lead (VPb) vacancies, as well as of the associates of the [V О •• 2Pb / i ] type, and by the emergence of various elastic stresses, which promotes the relaxation of the chemical bonds between atoms, caused by the deficiency introduced into the anionic sublattice of the Pb0,85Ba0,25Zr0,53Ti0,47O3−8 solid solution at the oxygen desorption process.

Single-phase Sr2FeMoO6-δ samples with different-degreesuperstructiral ordering Fe/Mo cations superstructural ordering (P, 76, 86 and 93 %) were obtained by the solid-phase technique. Based on the results of measuring the magnetic characteristics in the samples, we found that an increase in magnetization (26.41, 32.36 and 42.66 A·m2·kg–1), magnetic moment (1.33, 3.07 and 3.58 μB/f.u.) and Curie temperatures (422, 428 and 437 K) withparameter P (76, 86 and 93 %) can be explained by the presence of antistructural defects, as well as antiferromagnetic inclusions. This determines the redistribution of electron density, which is accompanied by the change in electronic configuration of a part of Fe/Mo cations. Based on the temperature dependences of the magnetic moment of the samples measured in ZFC and FC modes, and on small-angle polarized neutron scattering (SANS), we found that the samples are in a magnetically inhomogeneous state. An important result to mention is that we detected the difference between the slope of the SANS curves of samples with different oxygen content, which demonstrates a different microstructure of inhomogeneities. The main inhomogeneities are magnetic inclusions with the dimensions depending on the superstructural ordering of Fe/Mo cations. According to the Porod law, it was shown that the Sr2FeMoO6-δ samples with wave vector values 0.1 > q > 0.002 Å–1 contain polydisperse grains with a smooth surface. For q > 0.1 Å–1 a deviation from the Porod law is observed, confirming the presence of magnetic inhomogeneities with a diameter < 6 nm in the grains.

The kinetics of phase contents modification in the process of SrBaFeMoO6–δ crystallization from a stoichiometric mixture of SrCO3 + BaCO3 + 0,5Fe2O3 + MoO3 simple oxides using the solid phase method has been investigated. In the temperature region of 300–1200°С, a number of endotermic effects have been detected. Herewith, the first one (with maximum around 552°С) and the third one (with maximum around 743°С) are accompanying by the significant decrease of the mass of specimen. In the temperature range of 946–1200°С, the mass change of specimen is practically not observable, while the thermal effect is still present, and the specimen remains not single-phase one. This indicates the difficulty of the flow of solid phase reactions with the formation of solid solution of barium-strontium ferromolybdate. During analysis of the change of the phase composition consisting of a mixture of initial reagents of stoichiometric relation SrCO3 + BaCO3 + 0,5Fe2O3 + MoO3, it has been observed that with increasing temperature, complex compounds BaMoO4, SrFeO3 appear almost simultaneously, then SrBaFeMoO6–δ appears consequently. Thus, the compounds BaMoO4 и SrFeO3, are structure forming for the solid solution of barium-strontium ferromolybdate. With further temperature increase up to 770°С the formation of new compound ВаFeO3 with disappearing SrFeO3 was detected. In this case, the amount of double perovskite increases faster than that of barium molybdate. The main accompanying compounds at the crystallization of the SrBaFeMoO6–δ double perovskite solid solution are BaMoO4 and SrFeO3. It was established that at the initial stage of the interaction, the resulting solid solution of barium-strontium ferromolybdate is enriched with iron and its composition changes during the reaction in the direction of an increase of the molybdenum content, as in the case of other precursor combinations.

The sequence of phase transformations in the process of crystallization of the Sr2CrMoO6 by the solid-phase technique from a stoichiometric mixture of simple oxides SrCO3 + 0.5Cr2O3 + MoO, has been investigated. It was determined that the synthesis of the strontium chrome-molybdate proceeds through a series of sequential-parallel stages. By means of the differential thermal analysis and thermogravimetric analysis data, it has been established that five clearly expressed endothermal effects were observed in the temperature range 300−1300 K. It was found that during the studies of the phase transformations sequence in the process of the double perovskite synthesis, SrCrO3, SrMoO4 and Sr2CrO4 are the main concomitant compounds. Herewith, it has been observed that with the annealing temperature increase from 300 to 1270 K, the complex compounds SrCrO4, SrCrO3 (350−550 К) and SrMoO4, Sr2CrO4 (600−750 К) are emerging initially and practically simultaneously. It has been revealed with a subsequent temperature increase that in the temperature range 940−1100 К, the SrMoO4, Sr2CrO4 and SrCrO3 phase concentration dramatically drops with the emerging and growth of the Sr2CrMoO6-δ double perovskite. With that in the range up to 1120–1190 К, the main XRD reflexes intensity for the SrCrO3 and SrMoO4 lowers substantially, and their content in the samples at 1170 К is no more than 7.9%. During a consideration of the derivative of the SrCrO3, SrMoO4 and Sr2CrO4 phase transformation degree (|(dα/dt)|mах), at which their crystallization rates are maximal, it has been determined that |(dα/dt)|mах for the Sr2CrO4 corresponds to the maximal temperature 1045 К, which indicates the presence of considerable kinetic difficulties at the formation of the Sr2CrO4 phase. Thereafter this phase does not disappear and at its appearance the slowing down of the double perovskite growth takes place. On the base of investigations of the phase transformations dynamics for the obtaining of the single-phase Sr2CrMoO6-δ compound with the superstructural ordering of the Cr/Mo cations and improved magnetic characteristics, the SrCrO3 and SrMoO4 precursors were used with combined heating modes.

Characteristic properties of the formation of physical - chemical properties of a manganite with the composition La0.6Sr0.4MnO3-d were considered. It was determined that two titration current minima depending on the heating rate and the partial pressure of oxygen (pO2) exist at different temperatures, heating rates and partial pressures of oxygen. It is supposed that extreme values of the titration current are caused by breaking of bands of anions existing in two different forms with the tetravalent manganese, as well as by the excessive superstoichiometric oxygen which partially compensate the presence of Mn4+ cations, and by oxygen recovering the electroneutrality of the system appearing due to a decrease of the charge value due to the introduction of Sr2+. It was established that the activation energy of oxygen diffusion is decreasing and reached the minimal value 241 kJ/mole at pO2=5 Pa, with a subsequent increase up to ~273 kJ/mole at pO2= 150 Pa and d=0,004, with the increase of oxygen defects concentration in the La0.6Sr0.4MnO3-d anion sublattice. Concentration dependence of the activation energy of oxygen diffusion is motivated by a formation of the stressed layer, placed near the surface of grains which are depleted with oxygen and at the same time they are a buffer for the oxygen diffusion.

Composition materials on the base of Pb0,75Ba0,15Zr0,53Ti0,47O3 (PBZT) with micro-inclusions of Cu and Ni are prepared by a complex ceramic technology. This technology includes metallization procedures by means of the chemical deposition method from standard solutions of nickel and copper. At determination of correlation of the structure of PBZT composites and their dielectric properties it was shown that dielectric losses increase with decreasing temperature. This is caused by the domination of the real part of the complex dielectric permittivity.

The sequence of phase transformations during Sr2FeMoO6-d crystallization by solid phase method was studied for powders synthesized from the stoichiometric mixture of SrFeO3- x and SrMoO4 precursors. It was found that the synthesis of strontium ferromolybdate solid solution proceeds through a series of parallel chemical reactions. Reveals that at the beginning stage of interaction the initially formed Sr2FeMoO6-δ powder is enriched with iron. During the annealing process, the composition of strontium ferromolybdate changes and the molybdenum content increases upon further heating. It was found that the use of precursors reduces the annealing temperature.

Single-phase nanosized Sr2FeMoO6-δ powders were synthesized by citrate-gel method at pH = 4, 6, 9, with various degrees of superstructural ordering of Fe3+ and Mo5+ cations ( P = 65 % for pH = 4, P = 51 % for pH = 6 and P = 20 % for pH = 9). According to the XPS analysis results, mixed valence state of cations iron and molybdenum was established. With increasing of pH, the Fe2+ concentration value rises from 63 % to 72 %, whereas the Fe+3 concentration drops from 37 % to 28 %. According to the results of investigations of magnetization temperature dependence performed in ZFC (zero-field cooling) and FC (field cooling) modes a metastable superparamagnetic state in low-dimensional grains of Sr2FeMoO6-d ferrimagnetic powders at T < 19 K was established. In powders with pH = 4 the number of low dimensional grains is significantly larger than powders with pH = 6 and 9. This has led to their large magnetization value at T = (4,2-19) K.

Ferromagnetic-ferroelectric composite materials on the base of Pb0.85Zr0.53Ti0.47O3-Sr2FeMoO6-δ (PZT-SFMO) compound have been prepared by a complex ceramic technology and the citrate-gel synthesis. It was determined that the dielectric permittivity of a sample with a content of PZT of 55 wt. % and SFMO of 45 wt. % increases with temperature due to the rise of electrical conductivity and an influence of the dielectric dispersion caused by the Maxwell-Wagner relaxation. The electrical conductivity of the sample with a content of PZT of 35 wt. % and a content of SFMO of 65 wt. % possesses a clearly expressed frequency dependence, at temperature lower than 600 K, whereas at higher temperatures the electrical conductivity almost does not depends on frequency in the range 20 Hz-1 MHz. This is concerned with a considerable decrease of critical frequency at higher temperatures. At frequencies higher than 100 kHz and temperature lower than 600 K, the electrical conductivity increases by a power law.

Single-phase Sr2FeMoO6-d powders with various degrees of superstructural ordering of Fe/Mo cations and oxygen index d were obtained by solid-phase synthesis. With the help of X-ray phase analysis and neutron diffraction studies it has been established that the Fe-O1 and Mo-O2 values decrease with increasing oxygen content and the superstructural ordering of Fe/Mo cations increases, whereas the Fe-O2 and Mo-O1 bond lengths decrease, which leads to a decrease in the crystal lattice parameters and in the unit cell volume accordingly. This indicates an increase in the covalence of the bond along the axis (c), which stimulates the redistribution of the electron density from the (Fe/Mo-O2) layers to the (Fe/Mo-O1) layers and to an increase in the concentration of spin-polarized electrons with spins¯, which are located in the conduction band on Mo(t2g)¯ electron orbitals. When studying the dynamics of the change in oxygen non-stoichiometry and the degree of superstructural ordering it was found that the rate of desorption of oxygen is several times larger than the rate of Fe/Mo cations ordering.