By using the VASP package, within the framework of the DFT approach, the properties of the ground state of the SrFe1 – xMoxO3 – y oxide with the perovskite structure are calculated for the various values of molybdenum content and oxygen nonstoichiometry. It is shown that the doping procedure as well as the procedure of varying the oxygen content give rise to changes in the charge stage of oxygen ions in the system, which is accompanied by a shift of the Fermi level with respect to the invariant band structure (rigid band model) and the transition to the semimetal conduction type.

Министерство науки и высшего образования Российской Федерации Российское химическое общество им.Д.И.Менделеева Секция по химической термодинамике и термохимии Научного совета РАН по физической химии Сибирское Отделение Российской Академии Наук Институт неорганической химии им.А.В.Николаева СО РАН

Organic salts tetrabutylammonium borofluorate and tetraethylammonium borofluorate are simulated by molecular dynamics as pure forms and as part of a composite with α-Al 2 O 3 limited by the (110) plane. The obtained characteristic freezing points and structural change points agree with experimental data. In the composite, the amorphous organic salt transforms into a partially ordered state with a layered structure formed by contact interactions between the oxide and the salt.

Методом молекулярной динамики моделировались органические соли - тетрабутиламмония и тетраэтиламмония борофлюораты, в чистом виде и в составе композита с α-Al2O3, ограниченного плоскостью (110). Полученные характерные температуры – замерзания, изменения структуры, согласуются с экспериментальными данными. В композите аморфная органическая соль переходит в частично упорядоченное состояние со слоистой структурой, формируемой контактным взаимодействием оксида и соли.

Sodium polyanion phosphates can be used as cheap cathode materials for Na-ion batteries. One such material is sodium-iron ortho-pyrophosphate Na4Fe3(PO4)2P2O7 (hereafter NFPP). This compound demonstrates small changes in the volume of the unit cell during cycling, which indicates the possibility of its long-term operation, has an average operating voltage of 3 [V] in the Na-cell. Also, NFPP can be used as a cathode in a hybrid Na/Li electrochemical cell. When cycling in a hybrid cell, the joint intercalation of Na+ and Li+ ions occurs. In this paper, atomistic modeling methods are used to obtain additional information about the distribution of Li+ in the sample structure after ion exchange. The model used in the study demonstrates a good reproduction of the observed structure. The distribution of lithium in the structure of Na4-xLixFe3(PO4)2P2O7 (NLFPP) after (electro)chemical exchange has been established. The results show that incomplete electrochemical exchange may be associated with a low diffusion coefficient of Li+ across the electrolyte/cathode interface.

Oxides with perovskite structure SrFeO3 and SrCoO3 are ancestors of wide range of technologically important substances, used as oxide ionic conductors. Previously we use the substitution of the cations in the B positions by high-charge ions Mo6+ W6+ Ta5+ Nb5+ to modify the properties of this class of oxygen-deficient oxides. Doping with these elements suppressed phase transitions in oxides based on cobalt-ferrite strontium-barium, reduced the size of nanodomains and rise chemical and structure stability of these oxides. Now we performed the theoretical study of the influence of A- and B- substitution on electronic structure of SrFeO3 and SrCoO3 in the order to clarify how the doping by high-charge cations affects the properties and electronic structure of oxides.

The substitution of A and B cations in SrFeO3 and SrCoO3 oxides with the perovskite structure ABO(3) is studied using ab initio DFT calculations in terms of their effect on the structural and electronic properties of these compounds. It is shown that the main effect of Nb, Ta, Mo, W substituents refers to the local increase of the cohesive energy (the decrease of the total energy) of the oxides. This change may reach 10 kJ/mol per 1% of the B dopant.

The development of the theoretical background of a new relaxation technique based on pO(2) monitoring at the outlet of the continuous-flow fixed-bed reactor is presented. The model describes the relaxation kinetics of oxygen exchange between the nonstoichiometric oxide and the gas phase in a case when surface reaction is the rate -limiting step. The model takes into account the feedback between the oxygen exchange rate and the oxygen partial pressure in the reactor: the rate is affected by oxygen released or uptaken by the sample. In the frame of material-gas feedback approach the influence of the sweep gas flow rate on the relaxation rate constant is shown. An analytical expression which allows determining correct value of the key material kinetic characteristic (surface exchange rate constant) from experimentally measured relaxation rate constant is derived. The proposed feedback approach has the versatility: the correction of the relaxation rate constant is necessary not only for the novel oxygen partial pressure relaxation method, but also for the other traditional relaxation techniques when oxides possess high oxygen exchange rate that does not allow to maintain constant oxygen partial pressure in the reactor even with high sweep gas flow rate.

The phase composition and microstructure of samples of the La1-xCaxFeO3-y system prepared via a ceramic route were characterized by Mössbauer spectroscopy. In all cases, iron was found in the 3+ state. The ordering of anion vacancies in the samples with the composition in the range of 0.8 > x ≥ 0.4, which corresponds to a microheterogeneous solid solution, generates new distorted octahedral and fivefold/tetrahedral sites revealed by two typical sextets. The disordering of this solid solution and small (10-100 Å) sizes of domains with a perovskite, braunmillerite or Grenier phase structure caused the appearance of a superparamagnetic doublet, which grows with the Ca content up to x = 0.8 but disappears in the sample of pure braunmillerite. The appearance of Fe cations in a distorted coordination correlates with the increased activity of the samples with a microheterogeneous structure in the CO catalytic oxidation and with their reducibility by H2.

Structural changes under the conditions of intense shear strain in two- and three-dimensional models of solids with a Lennard-Jones interaction potential and an ionic potential were studied by molecular dynamics. Voronoi and Delone partitions were used to study the states of three-dimensional models. The spatial distribution of defects was analyzed, and the macroscopic characteristics of the models were determined. Plastic flow was shown to involve division of a substance into blocks more or less separated by disordered layers.

Mechanochemical synthesis of dicalcium ferrite with the perovskite structure from anhydrous or hydrated calcium and iron oxides was studied by XRD, DTA, IR spectroscopy, and Mossbauer measurements. The formation of Ca2Fe2O5 from anhydrous oxides during mechanical activation (MA) occurs at a high rate. Although hydrated oxides do not react during MA, Ca(OH)(2) dehydration and subsequent Ca2Fe2O5 formation in preactivated mixtures occur at much lower temperatures (the latter process, at 600 degrees C). The resulting product is well-crystallized and has a specific surface area of 13 m(2)/g, which is large enough for catalytic applications.

Intensive plastic deformation of 2D ionic system AB2O3 is computer simulated. It is shown that a deep reconstruction of the structure occurs during the plastic flow. It may be regarded as a result of the repulsive interaction of large cations which maintain the potential energy in the dislocation core and cause relaxation motion of ions.

The computer simulation of the processes proceeding under intensive mechanical action is carried out for two-dimensional Lennard-Jones crystals. The time and deformation dependencies of strain tensor, energy and quantity of structure disruptions is presented for different load intensities. It is shown that the energy absorbed by the crystal under macroscopic mechanical action is released in local regions that are several Angstrom-sized. The plastic flow occurs through dividing the initial structure into regions in which the atomic motion is to be correlated.