Papers by Keyword: Oxides

Abstract: In recent studies, multifunctional oxide thin films have been given attention because of their special properties, such as ferroelectricity, gas sensitivity, and magnetism. Ion beam irradiation arose as a well-developed technique for tuning such properties. This study investigates the ion beam irradiation effects of He, Ni, and Kr ions on BiFeO₃, SnO₂, and ZnO thin films, respectively. The study utilized the 2013 version of Stopping and Range of Ions in Matter (SRIM) software to identify ion trajectory distribution and oxygen target vacancy differences on the Transport of Ions in Matter (TRIM) calculation types at various ion energies. A greater distribution of ion trajectories and higher peaks of oxygen target vacancies in oxide thin films were generated from monolayer TRIM than full cascade TRIM for all ion–thin-film pairs. The monolayer TRIM is preferable for ion beam irradiation of oxide thin films with its greater oxygen target vacancies and ion trajectory distribution for better analysis of ferroelectric coercive fields, adsorbed oxygen ions interaction with gas molecules, and the emergence of green emission for photoluminescence. The use of SRIM allows an alternative yet more flexible way of analyzing beam irradiation effects on oxide films considered in this work without resorting to costly or sophisticated experimental setups, which are a usual approach considered in most of the work under this topic. As such, the results presented here provide an initial or complementary basis should irradiation effect experiments require analysis of ion trajectories and oxygen vacancies.

Abstract: The scientific basis for the production of a new composite material (1-x)PbSexPbSeO₃, where x=0-1, by oxidation with oxygen at temperatures of 500-550 °C and oxidation times of 0.5-4 h from the initial phase of PbSe in the form of powder, film or compact material, having a ferroelectric phase transition in disordered crystals is developed. On the X-ray spectra of the original PbSe samples oxidized at 500°C (oxidation time of 0.5 h) it has been found that the PbSe phase reflexes are predominately present, including the X-ray spectra of the original PbSe samples oxidized at 500 °C (oxidation time of 4 h) - PbSeO₃ monoclinic phase reflexes. For all other PbSe oxygen-oxidized samples at temperatures of 500-550 °C and within the time range of 0.5-4 h, X-ray spectra show the simultaneous presence of X-ray reflexes of both phases with the trend of increasing the PbSeO₃ phase as the oxidation time increases. Temperature measurements of the DC resistance of the PbSe samples revealed an abnormal change in electrical resistance at the initial oxidation stage for both the film and the compact material, and further oxidation contributed to the capsulation of PbSe grains by the dielectric casing PbSeO₃ and the gradual increase in the resistance of the material.

Abstract: The possibility of applying a hyperbolic model for calculating thermodynamic characteristics (the standard molar heat capacity, standard molar entropy) to the V–O system is shown. For calculation of the molar specific heat and entropy within the bounds of the model the general concept has been used: a thermodynamic parameter is divided into two components. The first component depends on the molar mass of a compound, the second one is determined by inter particle interaction. The dependence of the inverse value for the interaction heat capacity (entropy) on composition is of linear character within one region of quasi-equilibrium solid solutions (one region combines compounds with the same or similar structure type).The use of the model allowed refining the available experimental data on vanadium oxides and predicting the values of thermodynamic characteristics for compounds poorly studied in experiment.

Abstract: Introduction of refractory elements into alumina ceramics to improve its properties, is usually carried out by mixing the alumina with oxides of refractory metals. In this work this problem has been solved by pre-alloying refractory element with aluminum and subsequent dispersion of alloy in aqueous alkaline solutions. Characteristics of microstructure, phase composition and rheological properties of powders obtained by chemical dispersion of alloys Al-Mo, Al-V and Al-Zr with 10 wt.% refractory element in 20% aqueous sodium hydroxide solution, as well as the impact of heat treatment at 1250 oC on these properties, have been discussed. On the basis of X-Ray analysis (XRA) and electron microscopy the conclusion was adopted that heat treatment of powder leads to significant phase and structural transformations of such powders and is a necessary stage of preparation for sintering.

Abstract: This is a theoretical study of species profiles during the oxygen chemical diffusion in an acceptor doped oxide crystal driven by large changes in the ambient oxygen partial pressure. The oxide crystal containing three species: mobile oxygen vacancy, mobile electron, immobile dopant ion, is considered. Our analysis is based on the expression of the chemical diffusion coefficient obtained in the framework of the concept of conservative ensembles (Maier J., 1993). It is shown that the dependence of chemical diffusion coefficient on ambient oxygen partial pressure in double-logarithmic coordinates is divided into distinct intervals. For each pressure interval the chemical diffusion equation is reduced to the diffusion equation with a diffusion coefficient which exhibits a power dependence on concentration. First, we analyzed the chemical diffusion under pressure inside each interval. As a result two singularities on the species diffusion profiles can be found: an internal reaction diffusion front, and an ambipolar diffusion front. This ambipolar diffusion front is characterized by a step of the electron concentration, moving inside a specimen. Afterwards, we consider a crystal in which the range of partial pressure spans all considered pressure intervals.

Abstract: Triaxial ceramics are multiphased materials produced from natural raw material. That a small modification as much concerning in the composition from raw material a ceramic mass, may change several properties from ceramics. Thus, was included into the ceramic mass Al₂O₃ and Fe₂O₃, however both originated from pectin citrus plus salt the intended respective metal source. These oxides have a particular physical characteristic as high softness and high porosity. In addition to the ceramic mass containing 10% of clay, 25% kaolin, 35% feldspar and 30% of alumina (Ind. Alcoa) was inserted 6% of Fe₂O₃ and the full replacement of commercial alumina by Al₂O_3(pec). The result from these oxides are satisfactory mainly. Influencing in thermal contraction, in the reduction of the residual porosity and changing the final color inthe product.

Abstract: Recently, the theory of gradient-corrected electron-positron correlations in solids was improved and extended in order to avoid the adjustable, empirical parameter α which is now part of theory and a smooth function of the electron density.This new, parameter-free approach is applied to selected oxides in order to discuss their interstitial space morphology reflected by the positron charge distribution. In addition, the positron lifetime and affinity are calculated using a highly precise computational method. An attempt is made to correlate these quantities with the volume of the reduced formula unit.The results for some oxides - such as Li-ion battery cathode materials and high temperature superconductors - are discussed in detail and prospects for future experiments are given.

Abstract: Among the Aluminum casting processes, High Pressure Die Casting (HPDC) is an efficient, versatile and economic way for producing large number of components. Nevertheless, because of the elevated amount of rejected castings, it is important to know which are the main causes of defect formation and their effects on microstructure and mechanical properties. This paper presents, within the European MUSIC project, an overview of the preliminary correlations obtained studying both castings with defect generator geometry, referred to as Horse-shoe Reference Castings, and industrial demonstrators, referred to as Gear Box Housing. The deduced correlations between static mechanical properties and casting defects highlighted interesting trends in both cases.

Abstract: By method of dynamic calorimetry, in the temperature range between 298,15 and 673 K, isobaric heat capacity of polycrystalline ferrites Bі₂СаFe₄O₁₀, BіMgFe₂O_5.5, Bі₂MgFe₄O₁₀ was experimentally studied. Mathematical processing of experimental data made it possible to derive polynomial equation of temperature dependence of ferrites heat capacity for respective temperature ranges, in dependencies C⁰_p~f (T) of ferrite Bі₂СаFe₄O₁₀ a jump was detected in heat capacity at 625K associated with phase transitions of type II. The values of the thermodynamic functions C⁰_p(Т), H⁰(T) – Н⁰(298,15), C⁰(T), F^hh(Т) have been calculated. Standard values of thermodynamic functions were determined using the method of ion increments. The results obtained broaden thermodynamic data bank for complex inorganic crystalline compounds.

Abstract: δ-FeOOH nanosheets have been synthesized on a large-scale by a simple method using NH₃·H₂O as precipitant at pH 10. The samples were characterized by FESEM, XRD, TEM, FTIR and PPMS. The results of this characterization reveal that the complexes [Fe^III(OH)_n(NH₃)_m]³⁻ⁿ formed between Fe³⁺ ions and NH₃ favor nucleation and oriented growth of δ-FeOOH nanosheets. The influences of precipitant, the initial pH, and concentration of H₂O₂ on the structure and morphology of the as-prepared δ-FeOOH have been investigated. Magnetic investigations show that the δ-FeOOH nanosheets exhibit high coercivity.