Na2Ti307 and K2Ti409 have layered structures with alkali metals in their interlayer regions. H2Ti307 and 2 409• 20 were obtained by exchanges of the alkali metals for protons in HC1 solution. Water molecules were additionally incorporated in case of K2Ti409. Reversible ion exchange of the protonated forms to the original Na2Ti307 and K2Ti409 were examined by using NaOH, NaCl, KOH, and KC1 solutions with various concentrations. Dehydrations were also studied on the protonated titanates. A new compound, H2Ti8017, having a channel-type framework was formed on dehydration of 2 409• 20. The ion exchange and dehydration behaviors are related to the structure of layers in the titanates.The hydrolyses of Na2Ti307 (ca. 750 mg) and K2Ti409 (ca. 1000 mg) were performed in 200 cm3 of 0.5 M HC1 at 60 °C for 3 day. The acid solution was changed everyday in order to remove completely alkali from the compounds. The products were

Ca2AlMnO5+δ with a brownmillerite‐type structure can topotactically store/release a large amount of excess oxygen (about 3.0 wt.%) depending on temperature and the surrounding atmosphere in a highly reversible manner.

The electronic structures of a number of binary 3d transition metal and iron nitrides, some of which still need to be synthesized, have been investigated by means of spin-polarized first principles band structure calculations ( TB-LMTO-ASA). The chemical bonding in all compounds has been clarified in detail through the analysis of total and local densities-of-states (DOS ) and crystal orbital Hamilton populations (COHP). The binary transition metal nitride set includes ScN, TiN, VN, CrN, MnN, FeN, CoN and NiN, both in the sodium chloride as well as in the zinc blende structure type. Antibonding metal-metal interactions for higher electron counts are significantly weaker in the zinc blende type, thus favoring this structural alternative for the later transition metal nitrides.For binary iron nitrides, the stoichiometric phases a◊-Fe 16 N 2 , c∞-Fe 4 N, e-Fe 3 N, f-Fe 2 N as well as the recently synthesized (rf-sputtering) non-stoichiometric compounds c◊-FeN 0.91 and c+-FeN 0.5-0.7 have been investigated. There is experimental evidence that c◊-FeN 0.91 adopts the zinc blende structure type while c+-FeN 0.5-0.7 should crystallize in a defect sodium chloride type structure. For the stoichiometric phases, most numerical theoretical data are consistent with the measured ground state properties ( lattice parameters and magnetic moments) whenever experimentally available. The general trends concerning iron-nitrogen and iron-iron bonding have been elucidated; the role of nitrogen vacancies were simulated by a number of model calculations. It appears that potentially antibonding interactions are the source of local structural distortions in all of these phases.For c◊-FeN 0.91 , theory supports the proposed metallic zinc blende structure with a theoretical lattice parameter of 421 pm for the exact 151 composition. With respect to c+-FeN 0.5-0.7 in the defect NaCl structure type, we arrive at theoretical lattice constants between 389 and 398 pm, somewhat depending upon the nitrogen content.

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Here, we report the remarkable oxygen intake/release capability of a double perovskite BaYMn 2 O 5þδ . This oxide rapidly stores/releases a large amount of oxygen (>3.7 wt %) at moderate temperatures in a perfectly reversible manner. The oxygen intake/release behaviors of BaYMn 2 O 5þδ are clearly beyond those of any conventional oxides in terms of the magnitude and sharpness of the processes. It also appeared that this oxide exhibits a significant catalytic activity for flameless combustions of hydrocarbons, presumably owing to its oxygen-storage ability.