Here, we investigate various approaches of chemical substitution to enhance the phase stability of the oxygen storage material candidate, YBaCo4O7+δ, under oxygen-containing conditions. From the results of Sr-for-Ba and R-for-Y (where R is a rare-earth element) substitutions, it can be concluded that the smaller the unit-cell volume, the less the phase absorbs oxygen but the higher the phase-decomposition temperature. Studies on the YBa(Co0.95M0.05)4O7+δ samples with M = Mn, Fe, Ni, Cu, Zn, Al, and Ga, then reveal that partial substitution of Co with Al, Ga, or Zn efficiently suppresses the phase decomposition. Most importantly, through cosubstitution with Al and Ga, the phase decomposition can be completely avoided for the YBa(Co0.85Al0.075Ga0.075)4O7+δ sample without markedly sacrificing the oxygen storage capability. Finally, it is shown that, among the RBa(Co0.85Al0.075Ga0.075)4O7+δ samples with R = Y, Dy, Ho, and Lu, only those with R = Y and Lu remain stable under oxidizing conditions at high temperatures. Possible factors affecting the phase stability of YBaCo4O7+δ and its derivatives are discussed.

The complex cobalt oxide YBaCo 4 O 7+δ is an exciting material from both a fundamental scientific and an applied technological point of view. It has a unique ability to reversibly absorb and desorb large amounts of oxygen in an exceptionally lowtemperature range, which makes it a promising candidate for applications in which efficient oxide ion conductivity or large oxygen storage capacity is required. It has also been considered as a model system for geometrically frustrated magnetism, which originates from the nature of the layered crystal [a]

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Here we present oxygen-nonstoichiometric transition metal oxides as highly prominent catalyst material candidates to catalyze the industrially important oxidation reactions of hydrocarbons when hydrogen peroxide is employed as an environmentally benign oxidant.The proof-of-concept data are revealed for the complex cobalt oxide, YBaCo 4 O 7+δ (0 < δ < 1.5), in the oxidation process of cyclohexene. In the two-hour reaction experiments YBaCo 4 O 7+δ was found to be significantly more active (>60% conversion) than the commercial TiO 2 catalyst (< 20%) even though its surface area was less than one tenth of that of TiO 2 . In the seven-hour experiments with YBaCo 4 O 7+δ , 100% conversion of cyclohexene was achieved. Immersion calorimetry measurements showed that the high catalytic activity may be ascribed to the exceptional ability of YBaCo 4 O 7+δ to dissociate H 2 O 2 and release active oxygen to the oxidation reaction.

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We have prepared a set of polycrystalline samples of the metallic copper oxide La 4 BaCu 5Àx Co x O 13þd (0 x 0.35) and have measured the resistivity from 4 to 800 K. All the resistivities show metallic temperature dependence with a small magnitude less than 2 mX cm at 800 K, indicating that the metallic conduction is robust against impurities. The robust metallic conduction further suggests that this class of oxide is a promising candidate for electrical leads at high temperature, which might replace platinum. A detailed measurement and analysis on the Hall resistivity have revealed that at least two components are responsible for the electrical conduction, in which a large number of electrons of moderate mobility coexist with a much smaller number of holes of extremely high mobility. This large electron density well screens the impurity potential and retains the metallic conduction against 7% impurity doping. V C 2015 AIP Publishing LLC.

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New RMnO 3+ (R: Y, Ho;   0.35) Phases with Modulated Structure. -A series of hexagonal LnMnO 3 compounds (Ln: Y, Ho-Lu) are prepared by sol-gel synthesis using citric acid, Ln 2O3, and Mn(NO3)2 in diluted HNO3 (300 C, 12 h). The resulting gel is dried and calcined at 900 C and 1300 C (for 12 and 30 h, resp.). High pressure oxygenation is then performed for the preparation of O-excess compounds (autoclave, 250-380 C, 90-100 bar O 2). Within the latter, the heavily-oxygenated phases YMnO3.35 and HoMnO 3.34 are identified. Results from TG, XRD, and electron diffraction show that YMnO3.35 exhibits a hexagonal sub-cell (space group P63mc) and satellites associated with two modulation vectors resulting from the evolution of the hexagonal parent YMnO 3+ structure towards a reduced pyrochlore-type structure Y2Mn2O7-x in long-and short-range ordering. -(PARKKIMA, O.; MALO, S.; HERVIEU, M.; RAUTAMA, E.-L.; KARPPINEN*, M.; J. Solid State Chem. 221 (2015) 109-115, http://dx.