The thermodynamic characteristics of point defects and the mechanism of charge transfer in lanthanum cobaltite doped with strontium and nickel

The specific conductivity and thermal electromotive force (EMF) coefficient of lanthanum cobaltite doped with strontium and nickel La_0.9Sr_0.1Co_0.9Ni_0.1O_3−δ were measured over the temperature and pressure ranges 1023–1223 K and 10⁻⁶−1 atm. The oxide was found to exhibit metallic-type conductivity (800 Ω⁻¹ cm⁻¹ ≤ σ ≤ 1150 Ω⁻¹ cm⁻¹) and small positive thermal EMF coefficient values. A joint analysis of the thermodynamic characteristics of formation of point defects and external T and p _{O 2} parameter dependences of conductivity and thermal EMF showed that charge was transferred in the oxide by small-radius polarons according to the hopping mechanism. The role of polarons was played by electrons Me ^′_Co and holes Me ^•_Co localized on 3d transition metals. The isothermal dependences of the concentrations and mobilities of charge carriers on the degree of oxygen nonstoichiometry of the oxide studied were calculated.

     

Compositional dependence of the ion-exchange properties of a sorbent based on oxotitanium hydrophosphate

Effect of the degree of hydration and the phosphorus to titanium ratio in sorbents based on hydrated oxotitanium hydrophosphate on their sorption properties: constant of heterogeneous substitution of hydrogen ions by cations of sodium, cesium, and strontium and static exchange capacity, was studied.     

Efficient three-level scheme for parabolic equations in cylindrical coordinates in a region with a small hole

An efficient three-level scheme for parabolic equations in cylindrical coordinates is constructed in a region with a small hole. No axial symmetry is assumed. The convergence rate of the scheme is estimated under minimum requirements on the initial data. The estimates are uniform with respect to a small parameter—the inner diameter of the region. The order of convergence is τ + h ², τ^1/2 + h, τ + h, depending on the smoothness of the data.     

Well-known perovskites (cerates, cuprates, manganates): Problems and facts; A review of nontraditional approaches

Phenomena and processes either new or not studied in-depth occurring in perovskite oxides and in systems which contain these compounds are reported and summarized. The materials under consideration are well-known for specific properties, e.g., cerates of alkaline earths are high-temperature proton conductors, manganates are electrode materials of SOFCs and show the effect of colossal magnetoresistance or YBa₂Cu₃O₇ cuprates YBa₂Cu₃O₇ are “high-temperature” superconductors. The presented nontraditional approach consists of considering physical and chemical phenomena and processes, which do not relate to the indicated main properties of the compounds. For instance, BaCeO₃ undoped and slightly doped has partially cerium in the form of Ce⁺³, which provides the effect of blue luminescence which is controlled by thermochemical treatment; H₂YBa₂Cu₃O₇ manifests mixed proton-electron conduction at 400–550 K under water vapor of 100–300 Pa; La_0.67Ca_0,33MnO_2.84 can dissolve some part of water vapor as this occurs in traditional HTPC. The electrochemical cells Pd | HTPC | hydrocuprate | HTPC | Pd and the more simple one Pd | HTPC | Pd show e.m.f. values near 1 V under certain conditions after polarization by d.c. currents at 420–520 K under different atmospheres. The system water vapor — membrane of undoped BaCeO₃-hydride is described. Defect chemistry equations are used to describe some of the phenomena which are employed for the production and storage of pure hydrogen.     

IR-Fourier spectroscopic studies of structural changes in fullerenes C60 and C70-Toluene systems

The C₆₀-toluene and C₇₀-toluene complexes were studied by IR-Fourier spectroscopy. The complexes were obtained by crystallization from a toluene solution at room temperature. The changes in the IR spectra caused by the deformation of toluene molecules in the complexes allowed us to study the phase transitions in the fullerene-aromatic solvent systems.     

Light propagation in a helical medium with a large-scale periodicity

The propagation of light in helical media whose pitch greatly exceeds the radiation wavelength has been investigated. It is shown that such a system includes forbidden zones corresponding to the effect of ray turning. The propagation of an extraordinary ray corresponding to a very narrow forbidden zone has been analyzed in detail. The radiation wave field has been obtained both far from a turning point and in the close vicinity of such a point. It is shown that, in the vicinity of a turning point, mode transformation takes place and the wave acquires an elliptical polarization. The parameters of the ellipticity and the relations between the amplitudes of the waves passed through the forbidden zone and “reflected” from it are calculated.     

Photocatalytic activity of water-soluble tetrapyrrole compounds in the presence of amino-containing polymers

It was demonstrated that the activity of tetrapyrrole photosensitizers (TPSs) of singlet oxygen generation (dimegin, tetrasulfophenylporphyrin, and photoditasine) in the oxidation of tryptophan in the aqueous phase decreases in the presence of polymers containing free amino groups (chitosan and polyallylamine). The decrease of the activity is accompanied by the change of the electronic absorption spectra of the TPSs. Analogues of chitosan with screened amino groups (chitosan sulfate and carboxymethylchitin) or without amino groups (carboxymethylcellulose), as well as hexamethylenediamine, a low-molecular-weight compound, do not affect the activity of the TPSs. The regularities observed can be accounted for by the association of molecules of the tetrapyrroles initiated by the complexation of the TPSs having external salt groupings with free amino groups of the polymers.     

Implicit and efficient schemes for a parabolic equation in a spherical layer

An implicit and an efficient three-level scheme for a parabolic equation in spherical coordinates is constructed in a spherical layer. No axial symmetry is assumed. The convergence rates of the schemes are estimated under minimum requirements on the initial data. The estimates are uniform with respect to the inner diameter of the domain. The order of convergence is τ^α/2 + h ^α, α = 1, 2, depending on the smoothness of the data. The results remain valid for a domain without a hole.