Structure and properties of the layered perovskites in Sm-Ba-Co-Fe-O System

Perovskite oxide materials with the general formula of ABO3, where A is an alkali earth or rare earth metals and B is transition metals, have attracted much attention as cathodes for solid oxide fuel cells because of their high electronic conductivity and fast mobility of oxygen ions. The introduction of Ba2+ and Ln3+ ions with significantly different radii into the A-sites leads to a formation of layered perovskite-type structures which have formed due to the cations’ ordering in the alternating layers. Depending on the nature of rare earth and 3d metal, it was possible to obtain double LnBaM2O6-δ, triple LnBa2M3O9-δ, or quintuple Ln2Ba3M5O15-δ perovskites. The aim of the present work was studying the effect of Ln/Ba and Fe/Co ratio for the crystal and defect structure and properties of oxides in the Sm-Ba-Co-Fe-O system. Polycrystalline samples of SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ were prepared by the glycine–nitrate synthesis. Final annealing was performed at 1100°С in air during 120h with intermediate grindings, followed by slow cooling down to room temperature at a rate of about 100°/h. The structural parameters were refined by the Rietveld method using the Fullprof-2008 software. Transmission electron microscopy studies were performed using FEI Tecnai G2 30 UT microscope operated at 300kV. The changes of oxygen content in complex oxides were measured by coulometric titration method as a function of temperature and oxygen partial pressure. The absolute value of oxygen content in the samples was determined using a direct reduction in the TG cell by hydrogen flow and red-ox titration. Thermal expansion of samples was studied using Netzsch DIL 402C dilatometer within the temperature range 25 – 1100°С in air. Total conductivity and Seebeck coefficient were measured simultaneously using a 4-probe technique. The crystal structure of SmBaCo2−xFexO6-δ (0≤x≤0.5) was described by the orthorhombic ap×2ap×2ap cell (Pmmm sp. gr.), while SmBaCo2−xFexO6-δ (0.6≤x≤1.1) crystallized in the tetragonal structure, ap×ap×2ap cell (P4/mmm sp. gr.). The crystal structure of single-phase Sm2-εBa3+εFe5-yCoyO15-δ (ε = 0, y = 0.5–1.5; ε = 0.125, y = 0) determined by XRD was described as cubic (sp. gr. Pm3m). However, transmission electronic microscopy revealed that oxides possess tetragonal structure with 5-fold c parameter. The defect structure of oxides with double perovskite structure was described using the model based on the simple cubic perovskite SmMeO3 (Me = Co, Fe) as a reference state. Equilibrium constants and enthalpies of the point defects formation were refined. The concentrations of all defect species were calculated as functions of temperature and oxygen nonstoichiometry. The temperature dependencies of total conductivity for SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ possess maxima at approximately 300–350ºC in air. The partial substitution of iron for cobalt leads to a decrease in the conductivity value. Seebeck coefficient for all compounds reveals positive values within the entire temperature and oxygen partial pressure ranges that indicate predominant p-type conductivity. The dependencies of electrical conductivity and Seebeck coefficient versus oxygen nonstoichiometry were discussed on the basis of the defect structure models. The values of activation energy for fixed oxygen content values were calculated. This work was supported by the Russian Science Foundation (Grant № 18-73-00159

Structure and properties of commercially pure titanium nitrided in the plasma of a low-pressure gas discharge produced by a PINK plasma generator

The paper analyzes the surface structure and properties of commercially pure VT1-0 titanium nitrided in the plasma of a low-pressure gas discharge produced by a PINK plasma generator. The analysis demonstrates that the friction coefficient of the nitrided material decreases more than four times and its wear resistance and microhardness increases more than eight and three times, respectively. The physical mechanisms responsible for the enhancement of strength and tribological properties of the material are discussed

Combined surface modification of commercial aluminum

The paper analyzes research data on the structure and properties of surface layers of commercially pure A7-grade aluminum subjected to treatment that combines deposition of a thin metal film, intense pulsed electron beam irradiation, and nitriding in low-pressure arc plasma. The analysis shows that the combined method of surface modification provides the formation of a multilayer structure with submicro- and nano-sized phases in the material through a depth of up to 40 ?m, allowing a manifold increase in its surface microhardness and wear resistance (up to 4 and 9 times, respectively) compared to the material core. The main factors responsible for the high surface strength are the saturation of the aluminum lattice with nitrogen atoms and the formation of nano-sized particles of aluminum nitride and iron aluminides

Numerical simulation of discharge plasma generation and nitriding the metals and alloys

This research provides the numerical simulation of the plasma generation in a hollow cathode as well as the diffusion of nitrogen atoms into the metal in the low-pressure glow discharge plasma. The characteristics of the gas discharge were obtained and the relation of the basic technological parameters and the structural and phase state of the nitrided material were defined. Authors provided the comparison of calculations with the experimental results of titanium nitriding by low-pressure glow discharge plasma in a hollow cathode

Optimization criteria for entry into the consolidated group of taxpayers in order to create an effective tax mechanism and improve the social, economic development of regions in the Russian Federation

This article discusses the existing socio-economic development of regions. The social and economic development of the regions is directly affected by the tax ratio and mechanisms of their functioning, which are the subject of study for both foreign and Russian economists, as the state regulation of any economy is possible through tax relations between parties. In 2012, there was established the taxation of consolidated groups of taxpayers, which exists in many countries and provides payment of income taxes based on the total financial and business performance of the group. However, in our opinion, the requirements for entry into the group are much too high. The article presents a method that allows analyzing the changes in the number of potential participants of a consolidated group of taxpayers depending on the changes in the threshold of entry using indicators. These indicators can be based on the aggregate value of assets, or represented in terms of total revenue or the amount of taxes paid. The reduction in the existing criteria will optimize tax administration of the major taxpayers and more evenly redistribute financial flows between regions of Russia

Optimization criteria for entry into the consolidated group of taxpayers in order to create an effective tax mechanism and improve the social, economic development of regions in the Russian Federation

This article discusses the existing socio-economic development of regions. The social and economic development of the regions is directly affected by the tax ratio and mechanisms of their functioning, which are the subject of study for both foreign and Russian economists, as the state regulation of any economy is possible through tax relations between parties. In 2012, there was established the taxation of consolidated groups of taxpayers, which exists in many countries and provides payment of income taxes based on the total financial and business performance of the group. However, in our opinion, the requirements for entry into the group are much too high. The article presents a method that allows analyzing the changes in the number of potential participants of a consolidated group of taxpayers depending on the changes in the threshold of entry using indicators. These indicators can be based on the aggregate value of assets, or represented in terms of total revenue or the amount of taxes paid. The reduction in the existing criteria will optimize tax administration of the major taxpayers and more evenly redistribute financial flows between regions of Russia