High-Resolution Thermochemical Study of Phase Stability and Rapid Oxygen Incorporation in YBaCo4- xZn xO7+δ 114-Cobaltites.

The formation thermodynamics of YBaCo4- xZn xO7+δ ( x = 0, 1, and 3) oxides was determined by high-temperature oxide melt solution calorimetry. All of the studied oxides are thermodynamically metastable due to the tendency of cobalt to increase the oxidation state under oxidizing conditions as well as to significant bond valence sum mismatch for Ba and Y in 114-oxides. Complex phase evolution in YBaCo4O7+δ at 350-400 °C upon oxygen absorption was revealed using incremental precise oxygen dosing. The calorimetric results support phase changes seen during in situ X-ray diffraction structural studies and provide high-resolution measurement of the amount and energetics of oxygen absorbed by YBaCo4- xZn xO7+δ under equilibrium conditions.

Thermodynamics of Sr2NiMoO6 and Sr2CoMoO6 and their stability under reducing conditions.

The values of standard enthalpy of formation at 298.15 K and 1 atm for the double perovskites Sr2NiMoO6 and Sr2CoMoO6, measured by means of drop solution calorimetry, were found to be -2418.1 ± 12.4 and -2422.9 ± 9.6 kJ mol-1, respectively. Heat capacity of Sr2NiMoO6 and Sr2CoMoO6 was measured between 2 and 370 K using relaxation and adiabatic calorimetry, and the enthalpy increments - between 373 and 1273 K using drop calorimetry. Low-temperature magnetic and higher-temperature structural phase transformations in Sr2NiMoO6 and Sr2CoMoO6 were discussed from the thermodynamic point of view. Specific heat (Cp), standard enthalpy (ΔT0H0) and standard entropy (S0) functions were derived from the experimental data for both double perovskites. The values of Cp, ΔT0H0 and S0 at 298.15 K were determined to be 202.31 ± 0.61 J mol-1 K-1, 36.12 ± 0.18 kJ mol-1 and 231.3 ± 1.6 J mol-1 K-1 for Sr2NiMoO6, and 212.66 ± 0.64 J mol-1 K-1, 38.25 ± 0.19 kJ mol-1 and 244.4 ± 1.7 J mol-1 K-1 for Sr2CoMoO6, respectively. Additionally, using the thermodynamic data available, phase diagrams with respect to T and pO2 showing stability limits and decomposition products were calculated for Sr2NiMoO6 and Sr2CoMoO6. Though the cobaltite's stability range is wider than nickelate's both in terms of T and pO2, both complex oxides were found to be stable only at reasonably high temperatures and in oxidizing conditions, and metastable at low temperatures.

The defect structure and chemical lattice strain of the double perovskites Sr2BMoO6-δ (B = Mg, Fe).

The defect structure of B-site ordered double perovskites Sr2BMoO6-δ was analyzed. The defect structure model was proposed and successfully verified using data on oxygen nonstoichiometry of Sr2MgMoO6-δ and Sr2FeMoO6-δ. As a result, equilibrium constants of the defect reactions involved were estimated. Fe and Mo in Sr2FeMoO6-δ were found to be in the mixed oxidation state close to +2.5 and +5.5, respectively. Chemical strain of the Sr2FeMoO6-δ double perovskite lattice was studied by in situ high temperature XRD at 1100 °C depending on pO2. Parameter a of the Sr2FeMoO6-δ cubic cell was found to increase with decreasing pO2 because of lattice chemical expansion. The tetragonal polymorph of Sr2FeMoO6-δ was shown to exhibit transversal isotropy with respect to chemical expansion. It was also found that its crystal lattice expands in the ab-plane and simultaneously contracts along the c-axis when the oxygen content in the double perovskite decreases. In order to describe the degree of anisotropy of chemical strain a new phenomenological coefficient was introduced. This coefficient was shown to affect both the magnitude and change direction of an oxide cell volume caused by its reduction/oxidation. Excellent agreement between the chemical expansion along the a-axis calculated for both polymorphs of Sr2FeMoO6-δ according to the model recently developed and that measured experimentally was shown. Chemical contraction observed along the c-axis with a decreasing oxygen content in the tetragonal polymorph was also found to coincide completely with that calculated using the approach developed in the present study.

Oxygen nonstoichiometry, defect structure and oxygen diffusion in the double perovskite GdBaCo2O6-δ.

Oxygen nonstoichiometry of GdBaCo2O6-δ was studied by means of the thermogravimetric technique in the temperature range 600-1000 °C. The defect structure model based on the simple cubic perovskite GdCoO3-δ was shown to be valid for GdBaCo2O6-δ up to temperatures as low as 600 °C. Two independent methods, namely dc-polarization with the YSZ microelectrode and (18)O-isotope exchange with gas phase analysis, were used to determine the oxygen self-diffusion coefficient in the double perovskite GdBaCo2O6-δ. All measurements were carried out using ceramic samples identically prepared from the same single phase powder of GdBaCo2O6-δ. The experimental data on oxygen nonstoichiometry of GdBaCo2O6-δ allowed a precise calculation of the oxygen interphase exchange rate and the oxygen tracer diffusion coefficient on the basis of the isotope exchange measurements. The values of the oxygen self-diffusion coefficient measured by the dc-polarization technique were found to be in very good agreement with the ones of the oxygen tracer diffusion coefficient.

Oxygen content, crystal structure and chemical expansion of PrBaCo(2-x)Fe(x)O(6-δ) double perovskites.

PrBaCo2-xFexO6-δ (x = 0-0.6) double perovskites were shown to have a tetragonal P4/mmm structure in air over the complete temperature range investigated despite the oxygen content reaching a threshold value of 5.5 at temperatures from 850 °C for x = 0 up to 1078 °C for x = 0.6. However the P4/mmm→Pmmm structure transition was found to occur in PrBaCo2O6-δ under reducing conditions at temperatures from 500 °C at pO2 = 10(-3) atm down to 350 °C at pO2 = 10(-4) atm. The lattice chemical expansion along the a-axis and contraction along the c-axis, with decreasing oxygen content, 6 - δ, were found to completely compensate each other in the double perovskites and, therefore, their volume chemical expansion became negligible. As a result the cell volume linearly increases with temperature contrary to simple cubic perovskites.

[Characteristics of protein metabolism changes in oncology patients with surgical and combined treatment]. / Osobennosti izmeneneniia belkovogo obmena u onkologicheskikh bol'nykh s khirurgicheskim i kombinirovannym metodom lecheniia.

Combined approach (surgery and chemotherapy) have been acknowledged as the optimal treatment scheme in oncology. The purpose of this case study was to detect and compare the changes in metabolism emerging in combined treatment method for the purpose of working out, later, a therapeutic correction scheme to correct such changes. Two groups of patients, 20 subjects in each, were examined to establish a basic higher degree of the protein-and-energetic insufficiency and a changed immune response, due to which metabolism in patients with combined treatment normalizes slower than in patient with surgical treatment. Special scheme, worked out for the purpose, are needed to correct the progressing lesions.