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The pseudo-potential PAW method of the density functional theory is employed to study the localization of superstoichiometric oxygen in ferrite CaBaFe4O7 with the orthorhombic swedenborgite structure. The geometric characteristics of oxygen defects are determined by the crystal lattice relaxation procedure. It is shown that the formation of defects in calcium and barium coordination are energetically unfavorable. Oxygen intercalation into structural trigonal iron-oxygen and Kagomé layers is more favorable. In these layers, two edge-sharing Fe2O5 bipyramides are formed instead of FeO4 tetrahedra connected via one oxygen atom. The structural instability of ferrite CaBaFe4O7 is shown to be caused by the population of anti-bonding 2p O states during oxygen intercalation. The asymmetric location of the intercalated oxygen ion relative to the neighboring iron ions promotes the appearance of local electric polarization, which can induce ferroelectric effects in the presence of ferromagnetic order. [ABSTRACT FROM AUTHOR]

Cation ordering/disordering features in perovskite-like oxides LnBaMn2O6−δ where Ln = Pr, Nd, Sm were studied by means of a combination of thermogravimetry and X-ray powder diffraction techniques in a wide range of temperatures. Variation in lanthanide size was shown to be an effective route for the shift in temperature of ordering and disordering. As a result, it was found coexistence of three different phases which can be obtained separately: disordered cubic Ln0.5Ba0.5MnO3–δ, and ordered kinds of LnBaMn2O6−δ having δ ≈ 0 or 1.0. The respective ambient conditions around stability boundaries for the whole studied phases were successfully determined. Additionally the main reasons for inducing ordering as well as disordering processes were clarified by the use of in-situ XRD and DSC methods. A combination of the experimentally obtained data with the results of limited studies reported in literature allows one to organize the available information about double manganites giving some explanation of ordering processes as well as appropriate conditions used to obtain oxides with desired ordering degree. [ABSTRACT FROM AUTHOR]

We have studied the behavior of Y1 –yCayBaCo4 –xMxO7 + δ solid solutions in cyclic oxygen absorption/release processes in air at temperatures in the range 350–580°C. Y0.8Ca0.2BaCoO7 + δ has been found to absorb the largest amount of oxygen: 0.52 wt % (325 μmol O/g). The incorporation of calcium and iron into the structure of the YBaCo4O7 + δ cobaltite has been shown to shift the oxygen exchange process to higher temperatures and increase the oxygen storage capacity of the material. [ABSTRACT FROM AUTHOR]

It is shown that an excess of Dy in A‐site (in amount of 0.2 in formula units) allows synthesizing a single‐phase perovskite‐related oxide with the 123‐type structure at 1100 °C in air. Cobalt ions completely fill the octahedrally coordinated positions in the structure of 123‐type Dy1.2Ba1.8Fe1.8Co1.2O8‐δ, while iron together with excess Co is in the pyramidal oxygen coordination. The oxygen content at room temperature of 7.86 decreases with temperature. A slight increase in the slope of thermal expansion observed at T >200 °C. The electrical conductivity, carried out mainly by holes, increases non‐linearly with temperature, reaching a maximum value 14.8 S ⋅ cm−1 at 900 °C. Magnetic measurements allow assuming that Fe3+ are in low spin state, all Co2+ ions are in high spin, and Co3+ can be split into several states depending on coordination. [ABSTRACT FROM AUTHOR]