Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Method of quantitative determination of chemical composition of substance and binding energy of core electrons

Abstract: analysis of materials with use of X-radiation, nondestructive analysis of chemical composition of multicomponent materials and determination of binding energy of core level of atom being in certain chemical state. SUBSTANCE: method includes measurement of line of photoelectron spectrum of at least one element, its decomposition by known set of elementary components corresponding to various chemical phases and known sequence of binding energy of core electrons of selected element in these phases, minimization of functional of errors between measured spectral line and summary calculated envelope of set of elementary components with selection of their amplitudes and width in the capacity of free parameters and determination of sought-for composition by relative contribution of these components into decomposed spectral line with account for stoichiometry of chemical phases. In correspondence with formula of invention above-mentioned operations are carried out per each line of two or more selected elements, binding energy of elements in various chemical phases being taken as free parameters and results obtained for all spectral lines being compared. Free parameters are varied till results match with due account of specified error. EFFECT: possibility to determine both chemical composition of complex compounds and binding energy of elements without use of standards. 6 dwg, 2 tbl

Deposition and Characterization of Ultrathin Ta2O5 Layers Deposited on Silicon From a Ta(OC2H5)5 Precursor

Abstract: Ultra-thin tantalum pentoxide (Ta2O5) layers of thicknesses ranging from 6 to 10 nm were deposited by low pressure chemical vapor deposition from Ta(OC2H5)5 on rapid thermal nitrided silicon substrates. Films were annealed in UV-O3 at 450°C, in dry O2 at 750°C or by using a combination of these two treatments. The physico-chemical properties were studied by TEM and SIMS. Results showed an oxidation of the interfacial region during annealing. The C and H contaminants are reduced during the O2 post-deposition treatment, and this step may also lead to a modification of the chemical state of C in Ta2O5. Both capacitance-voltage and current-voltage measurements were performed on Al/Ta2O5/Si structures. Excellent electrical properties were recorded: high dielectric constant (between 14.8 and 19 in the case of the double step annealing, which corresponds to an equivalent SiO2 thickness ranging from 2.0 to 2.3 nm), low leakage current densities (close to 5×l0−9 A.cm−2 @ lMV.cm−1) and promising long-term reliability.

Investigation on Preparation and Electrical Properties of Novel Perovskite Cathode Materials Doped with Multi-Elements for IT-SOFC

Abstract: To develop novel cathode materials with high electrical performances for intermediate temperature solid oxide fuel cells (IT-SOFCs) and optimize the preparation process, perovskite-type oxides Pr1-x-ySrxCayCo1-zFezO3-δ (x=0.1, 0.2; y=0.1, 0.2; z=0.2, 0.3, 0.4; denoted as PSCCF-81182, PSCCF-72173 and PSCCF-62264) were prepared by solid state reaction. The formation process, phase structure and microstructure of the prepared samples were measured using TG-DTA, FT/IR, XRD and SEM techniques. The mixed conductivity of the samples was measured using DC four-terminal method in the range of 150-950 °C. Chemical state of the elements was measured by XPS experiments. The results show that the prepared samples PSCCF-81182, PSCCF-72173 and PSCCF-62264 exhibit a single phase with cubic perovskite structure after sintered at 1200 °C for 6 h. The mixed conductivity of the samples increases with temperature up to a maximum value, and then decreases. At lower temperature, the conductivity follows small polaron hopping mechanism. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. At intermediate temperature (600-800 °C), the mixed conductivity values of the prepared samples are all much higher than 100 S•cm-1，and can meet the demand of cathode materials for IT-SOFC. XPS tests show that Co and Fe elements in PSCCF-72173 are all of + 3 and + 4 valence. Absorbed oxygen can also be found from the XPS patterns, which is related to the concentration of oxygen vacancies in the perovskite-type oxides.