Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Sulfophenylanthranylic acid as a new reagent for palladium

The use of diphenyl reagents bearing electron-withdrawing substituents in catalymetric analysis was studied using sulfophenylanthranilic acid as an example. A selective catalytic effect of palladium(II) on the oxidation of sulfophenylanthranilic acid by cerium(IV) sulfate in a weakly acid solution was found. The reaction rate was studied as a function of component concentrations, solution acidity, and temperature. A procedure for determining palladium(II) was developed and tested using model mixtures and a KP-5 sample of complex composition.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 144–148. Original Russian Text Copyright © 2005 by Burmistrova, Mushtakova, Nikonorov.     

Triphenylamine-4-sulfonic acid in the catalymetric determination of platinum metals

The catalytic activity of Ir(IV), Rh(III), and Ru(IV) was studied in the reaction of the oxidation of triphenylamine-4-sulfonic acid by sodium periodate in a weakly acidic medium. The main analytical characteristics of triphenylamine-4-sulfonic acid were found out. The optimum conditions of the indicator reaction (concentrations of components, acidity, and temperature dependence) were selected. Procedures for determining Ir(IV), Rh(III), and Ru(IV) were proposed and tested with model mixtures.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Processing of NMR,UV, and IR spectrometric data prior to chemometric simulation by independent component and principal component analysis

We consider methods for the mathematical preprocessing of signals in the spectrometric analysis of multicomponent mixtures using chemometric algorithms aimed at adjusting the baseline, experimental noise, and random shift of spectral bands. Practical examples of using simple mathematical operations (scaling, centering, derivatization) are given. The effectiveness of algorithms is illustrated by a wide range of spectroscopic signals (electronic absorption, IR, and NMR spectra) combined with chemometric methods of principal component analysis and independent component analysis.     

Electronic structure of molecules of diphenyl bridge compounds

Using the CNDO/2 method, we have calculated the valence electron density distribution in molecules of diphenylamine and its 13 derivatives with the substituents COOH, NO₂, OCH₃ on the aromatic rings of ionized forms of some diaryl amines, and also 4-amino- and 4-amino-4-adnitro substituted compounds with bridge groups NH, O, S, CH₂, CH=CH and analogous diphenyl derivatives. We have shown that independently of the nature of the bridge group, the principle of uncoupling of the aromatic rings is basically retained. Strong long-range effects of the substitutents along the chain of chemical bonds are not apparent. We have calculated the electrostatic molecular potential of the indicated compounds. We have established correlations between the electrostatic molecular potential and the protonization constants, the oxidation-reduction potentials of diarylamines; and also between the electrostatic molecular potential and the reaction rate constant for acylation of primary bridged amines at the amino group.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 84–88, January–February, 1985.