Tuning of water and hydroxide content of intercalated Ruddlesden-Popper-type oxides in the PrSr3Co1.5Fe1.5O(10-δ) system.

A series of hydration experiments of the Ruddlesden-Popper phase PrSr(3)Co(1.5)Fe(1.5)O(10-δ) with varying levels of oxygen nonstoichiometry were performed with the goal to clarify phase formation and underlying mechanisms and driving forces. The hydration reaction is most intense for partly reduced samples with a vacancy concentration corresponding to δ ≈ 1. Fully oxidized samples show little or no tendency toward hydration. Presence of oxygen vacancies acts as a prerequisite for hydration. Probably, the basicity of the materials owing to A-site cations is another contributing factor to the hydration ability. Under CO(2) free conditions pure hydrates and oxide hydroxides are formed. In CO(2)-containing atmosphere, additional carbonate anions are easily incorporated into the hydrate, probably at the expense of hydroxyl groups. The I-centered PrSr(3)Co(1.5)Fe(1.5)O(8)(OH)(2)·1H(2)O achieves a highly expanded c-axis upon the topochemical insertion reactions. In situ powder synchrotron X-ray diffraction (SXRD) shows that the hydrate converts to an oxide hydroxide, PrSr(3)Co(1.5)Fe(1.5)O(8)(OH)(2), at 70 °C with a primitive orthorhombic unit cell. Upon heating above 170 °C, an I-centered product is formed for which further dehydroxylation occurs at around 400-500 °C. Rietveld refinement of SXRD data shows that the absorbed water molecules fill the tetrahedral voids of the [AO](RS) rock salt layer of the monoclinic hydrate.

Niobium(V) oxynitride: synthesis, characterization, and feasibility as anode material for rechargeable lithium-ion batteries.

The decomposition reaction of niobium(V) oxytrichloride ammoniate to the oxynitride of niobium in the 5+ oxidation state was developed in a methodological way. By combining elemental analysis, Rietveld refinements of X-ray and neutron diffraction data, SEM and TEM, the sample compound was identified as approximately 5 nm-diameter particles of NbO(1.3(1))N(0.7(1)) crystallizing with baddeleyite-type structure. The thermal stability of this compound was studied in detail by thermogravimetric/differential thermal analysis and temperature-dependent X-ray diffraction. Moreover, the electrochemical uptake and release by the galvanostatic cycling method of pure and carbon-coated NbO(1.3(1))N(0.7(1)) versus lithium was investigated as an example of an Li-free transition-metal oxynitride. The results showed that reversible capacities as high as 250 and 80 A h kg(-1) can be reached in voltage ranges of 0.05-3 and 1-3 V, respectively. Furthermore, a plausible mechanism for the charge-discharge reaction is proposed.

Interstitial oxide ion conductivity in the layered tetrahedral network melilite structure.

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La(1.54)Sr(0.46)Ga(3)O(7.27) stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02-0.1 S cm(-1) over the 600-900 degrees C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions.