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This study evaluates the redox energetics of LaMO3−δ (M=Sc–Cu) perovskite-type oxides via generalized gradient approximation (GGA) to DFT. Two different approaches to redox energetics of oxygen deficient perovskites of strongly non-stoichiometric (δ=0.5) and dilute defect limits (δ→0) are studied. In the first approach the enthalpies of oxidation are calculated using the stoichiometric end-compounds of LaMO3 and LaMO2.5. The most common structures for the reduced lanthanides and strontides similar to the ones experimentally reported for SrMnO2.5, SrFeO2.5, and LaNiO2.5 are considered. The second approach to the oxidation enthalpies termed (δ→0) follow the trend observed experimentally. This approach represents the experimental conditions of the measured oxygen enthalpies, and is hampered less by the artificial features due to spurious self-interaction errors in GGA.

An experimental study of the oxygen non-stoichiometry and redox thermodynamics of LaMn1 − xCoxO3 ± δ (x = 0.25 and 0.75) is presented. The system shows partial solid solubility of LaCoO3 in LaMnO3 and vice versa. While both samples consist of two phases at room temperature, quenching experiments show that the x = 0.25 sample is single phase at high temperatures for the whole range of study, 0.6 < − log(pO2/atm) < 14. The x = 0.75 sample consist of two phases even at high temperatures. This does not necessarily represent a problem for applications, and both samples are studied in details. The oxygen non-stoichiometry versus oxygen partial pressure are measured at three temperatures of 1223, 1273, and 1323 K by coulometric titration and thermogravimetry, for x = 0.25 and 0.75, respectively. The extracted enthalpies of oxidation do not vary significantly with stoichiometry, and are − 680 ± 40 and for x = 0.25 and 0.75, respectively. These data and analyses of literature data for LaMnO3 and LaCoO3 show that the enthalpy of oxidation varies nearly linearly with x. Solid solution thermodynamic models are used to analyze the redox mechanism.

The oxygen non-stoichiometry and redox thermodynamic properties of the LaFe1 − xCoxO3 − δ system (x = 0.25 and 0.75) are studied. At low temperatures, the LaCoO3 and LaFeO3 systems show partial solid solubility. At 1,273 K (in air), both compounds are single phases and are orthorhombic and rhombohedral for x = 0.25 and 0.75, respectively. Thermogravimetry has been used to measure the oxygen non-stoichiometry versus oxygen partial pressure at three temperatures, 1,223, 1,273, and 1,323 K. Redox thermodynamic quantities are extracted directly from the oxygen non-stoichiometry curves. The extracted enthalpies of oxidation do not vary significantly with stoichiometry, and for x = 0.25 and 0.75, they are −640 ± 60 and −440 ± 60 kJ (mol O2)−1, respectively. Ideal solid solution thermodynamic models are used to analyze the redox mechanisms.

The generalized gradient approximation to density functional theory is benchmarked for the calculation of formation enthalpies of lanthanide perovskite-type oxides LaMO3 (M = Sc–Cu). Three different reaction pathways (from elements, mono and sesquioxides) have been investigated and the systematic errors associated with electron correlation due to overbinding of the oxygen molecule, electron self-interaction within localized 3d states, and geometrical relaxations are analyzed by critical comparison with a large number of experimental data. Calculated formation enthalpies from elements and sesquioxides are in good agreement with experiment when the overbinding of O2 is corrected for using the Wang ad hoc factor of 131 kJ mol−1 O2. By contrast, the calculated formation enthalpies from monoxides are systematically too low which are attributable to strong self-interactions due to localized 3d states in MO. The effects of relaxation and choice of magnetic structure on the enthalpies of formation are analyzed.

This article presents a new coulometric titration setup and describes the principles of operation, the main precautions to be taken into account to reduce the systematic errors, and evaluates the working range and the accuracy of the measurements. The major source of error, the oxygen leakage, is studied in detail and modeled based on leakage of oxygen through the YSZ solid electrolyte. Decreasing the difference in chemical potential of oxygen between inside and outside of the cell is studied as an applied measure to decrease the oxygen leakage. Flushing the pumping solid electrolyte by N2 shows a reasonable improvement. Eventually, oxygen non-stoichiometry of SrFeO3−δ is measured at 1273 K in the oxygen partial pressure range of 0.6 < −log(pO2/atm) < 12. The resulting values are in good agreement with the literature.

I løpet av de neste 30 årene vil nye varmerekorder gjøre det hvite Polhavet blått og åpent om sommeren. De lokale og globale konsekvensene er ukjente, men trolig store. Norge bør sette av minst ti år og en milliard kroner til vårt største forskningsprosjekt noensinne. Målet er å forberede oss og resten av verden på et blått Polhav. Norge er den arktiske havnasjonen med tradisjonen, erfaringen, infrastrukturen - og dermed et ansvar - for at verden skal forstå og forberede seg på denne store naturendringen. Framtidens Polhav er et nasjonalt faglig initiativ som utvikles for å løfte kunnskapen om klima, miljø, politikk og ressursutviklingen i Polhavet i årene som kommer. Konsortiet bak initiativet består av 16 institusjoner: Akvaplan-niva, FFI, FNI, Havforskningsinstituttet, Meteorologisk institutt, NERSC, NGU, NORCE, Norsk Polarinstitutt, NTNU, NUPI, SINTEF, UiB, UiO, UiT og UNIS.