Novel Features of Complex Oxides

I this project we have been working on producing oxides that may find application as magnetic sensors, magnetic storage devices, in oxide fuel cells, chemical sensors and catalysts. For such oxides there is often a strong correlation between the chemical composition, atomic arrangement and its physical- and chemical properties. This makes it extra exciting to explore them. In our search for new oxides, which may show exotic properties, we combined experimental work with theoretical calculations. The oxides we have focused on are denoted Ruddlesden-Popper (RP) type oxides. RP oxides can be written by the general formula An+1BnO3n+1, where A and B are metal atoms. This family of oxides is not so well understood. One important reason for this is that they are very challenging to synthesize. In addition their very fine details with respect to atomic arrangement is difficult to get completely correct, which is important if you aim at understanding how they act as magnets or how strong conductors they are. In this project we have succeeded in making completely new compounds taking the Ruddlesden-Popper type structure. One of them has the chemical formula La4Ni2AlO10. La4Ni2AlO10 is a strong magnet at low temperatures, but the compound it is derived from, La4Ni3O10, is a weak magnet. The change in magnetic properties is linked to the change in electronic configuration when some on the nickel atoms are replaced by aluminum. Some of the other compounds we have synthesized in this project are successfully converted to hydrated phases and hydroxides by reaction with water. By combining X-ray and neutron diffraction we have established the atomic arrangement of the compounds. We have observed that reactivity with water is facilitated at not too high temperatures. On the other hand, if the reaction temperature is to low, kinetics becomes a problem. For that reason a tradeoff in reaction temperature is essential. We have been working on understanding why some the RP oxides react with water and accommodate it in the layered structure. We believe the reactivity toward water is linked to oxygen content of the samples and how flexible the B-atom is in changing oxidation state. Most of the oxides we produced in this project are gray-blackish powders. However some few selected oxides were prepared in addition as super thin films. For example La4Ni3O10 is made as a thin film. To the best of our knowledge, we are the first group that has been successful in making a thin film of a RP3 phase. Finally, in order to be successful in this project it became important for is to collaborate with other groups both nationally and internationally.

Complex oxides exhibit a wide range of properties that give rise to a number of applications within future energy and IC technologies. The scientific program of this project addresses structure-property relations of Ruddlesden Popper type oxides, and with focus on three challenging themes that represent novel directions: - Tuning of electronic and structural properties as basis for novel phenomena in Ln4Ni3O8 and Ln1+xSr3-xFe3O8 (Ln = rare earth element) based materials - Water absorption in oxygen defe ct complex oxides; understanding mechanisms as basis for new compounds with tunable chemistry - Epitaxial thin films of RP3 oxides - exploring anisotropic properties It is emphasized that synthesis, characterization, advanced diffraction experiments and computational modeling will be closely interwoven in these efforts. This is firmly believed to enhance the scientific output of the project, both with respect to quality and quantitative wise. The project will involve significant national (IFE) and inter national collaboration (France, UK, India). In particular the collaboration with IFE at Kjeller will contribute to increased use of neutron scattering techniques in Norway, being of relevance in a long term perspective towards ESS.