Role of B-site ion on proton conduction in acceptor-doped Sm2B2O(7-δ) (B = Ti, Sn, Zr and Ce) pyrochlores and C-type compounds.

Proton conduction in three pyrochlores, Sm(1.92)Ca(0.08)B(2)O(7-δ), B = Ti, Sn, Zr and one phase with a related C-type fluorite superstructure, B = Ce, has been investigated. The samples were prepared by solid state reaction. Infrared spectroscopy measurements and thermogravimetric analysis were carried out to study the extent of proton dissolution and determine its dependence on the B-site ion. Electrochemical impedance spectroscopy, performed on heating and cooling pre-hydrated samples, confirmed significant levels of proton conduction for Sm(1.92)Ca(0.08)Ti(2)O(7-δ) and Sm(1.92)Ca(0.08)Sn(2)O(7-δ) up to T∼ 500 °C. In comparison the B = Zr and Ce samples revealed lower levels of proton conductivity, confined to temperatures below ∼ 400 °C. Proton diffusion coefficients of 3.36 × 10(-8), 1.73 × 10(-9), 5.53 × 10(-10) and 2.78 × 10(-11) cm(2) s(-1) were determined at 300 °C for samples with B = Ti, Sn, Zr and Ce respectively. The proton mobility of Sm(1.92)Ca(0.08)Ti(2)O(7-δ) is therefore approximately one order of magnitude lower than that found in yttrium-doped perovskite phases such as BaZrO(3) and BaCeO(3).

A multi-proxy study of anaerobic ammonium oxidation in marine sediments of the Gullmar Fjord, Sweden.

Anaerobic ammonium oxidation (anammox) is an important process for nitrogen removal in marine pelagic and benthic environments and represents a major sink in the global nitrogen cycle. We applied a suite of complementary methods for the detection and enumeration of anammox activity and anammox bacteria in marine sediments of the Gullmar Fjord, and compared the results obtained with each technique. (15) N labelling experiments showed that nitrogen removal through N2 production was essentially limited to the upper 2 cm of the sediment, where anammox contributed 23-47% of the total production. The presence of marine anammox bacteria belonging to the genus 'Candidatus Scalindua' was shown by 16S rRNA gene sequence comparison. FISH counts of anammox bacteria correlated well with anammox activity, while quantitative PCR may have underestimated the number of anammox bacterial 16S rRNA gene copies at this site. Potential nitrogen conversion by anammox ranged from 0.6 to 4.8 fmol N cell(-1) day(-1) , in agreement with previous measurements in the marine environment and in bioreactors. Finally, intact ladderane glycerophospholipid concentrations better reflected anammox activity and abundance than ladderane core lipid concentrations, most likely because the core lipid fraction contained a substantial fossil component, especially deeper in the sediment.