Defect chemistry of oxide interfaces by first principles calculations - DECOXIF

Oxide materials possess a wide variation in physical properties with potential technological applications. Many of these properties arise from defect in the crystal lattice, while other properties are impeded by such defects. It is challenging, but crucially necessary, to control the concentration and type of point defects during materials preparation. When devices and electronic components are made smaller, interfaces and defects at interfaces will have a larger impact on the properties. Through this project we want establish general rules for how to control the type of defects, where they accumulate, and their impact on the physical properties. Such knowledge will contribute to the development of materials for memory technology, sensors, batteries and fuel cells. Some combinations of interfaces and defects are anticipated to display novel physical properties, like conductivity or magnetism, which are not obtainable in a single phase bulk material. In this project we simulate multiferroic oxides with special attention to interfaces between a thin film of the material and the substrate the material is grown on. We also study internal interfaces within the multiferroic materials in the form of domain walls between ferroelectric domains where all the electric dipoles point in the same direction. Electronic structure calculations have been used to study lattice imperfections, dopants and impurities at interfaces. By simulating materials at an atomic scale the impact and importance of defects can be evaluated on a length scale and with an energy resolution not obtainable with currently available experimental methods.

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In order to understand the chemistry of point defects at oxide interfaces the DECOXIF project will apply the principles of solid state chemistry to epitaxial interfaces and domain walls in multiferroic materials. We will use density functional theory (DFT ) to simulate point defects at oxide interfaces to study their energetic stability and impact on the electronic and crystallographic structure, and to predict physical properties like electrical conductivity and magnetic order. From an experimental point of view the preparation and characterization of oxide interfaces is challenging. By using the "DFT microscope" we can investigate in detail the thermodynamic stability of a large number of combinations of domain walls and point defects to assess which are likely to form in real systems. Epitaxial strain conditions will be tuned computationally to establish the interaction between lattice strain and defects. The local effect of impurities on the stability, crystal structure and electronic properties of oxi de interfaces will be investigated. The output of the DECOXIF will be intuitive guidelines, based on solid state chemistry, for designing enhanced interface functionality through point defects. This is enabling knowledge for future innovations in oxide el ectronics. The chemical approach to point defects at interfaces is highly transferable to related areas of materials science, like fuel cells, batteries and solar cells. Two PhD candidates will be educated and the research group will expand its activity i n a new and fundamental direction in collaboration with leading international experts. The project will strengthen computational materials science at both an institutional and a national level, and utilize the resources of the Norwegian metacenter for com putational science NOTUR.