Disputas: Ravindran Vidya

Prøveforelesning

Bedømmelseskomité

Professor Claudia Ambrosch-Draxl, University of Leoben
Professor Lars Nordstrøm, Uppsala Universitet
Professor Johan Taftø, Universitetet i Oslo

Sammendrag

Among the inorganic materials, transition-metal oxides have acquired special attention owing to the vast diversity of structures and a wide spectrum of exotic properties (like superconductivity, colossal magneto-resistance, multiferroism, metal-insulator transition) with numerous potential technological applications. The present thesis has focussed on magnetic oxides in complex structures, in particular those consisting of transition-metal atoms in two different valence states. A major theme of the project has been to understand the intrinsic properties of such materials by theoretical calculations. We have used a number of highly accurate, state-of-the-art computational tools based on the density-functional theory, an invention for which Prof. Walter Kohn bagged Nobel Prize in Chemistry in 1996.

One of the major findings of this project is that, valence states of the constituents in a compound can not be approximated as simple formal oxidation states according to a pure ionic model. The mixture of bonding forms with ionic, covalent, and metallic nature must be taken into account for the assignment of valence states. Therefore, elaborate theoretical band-structure studies like those handled in this project should be consulted for such assignments.

The structural arrangement of constituents of a compound appears in general to be more decisive for the electronic band structure and the electronic conductivity rather than the individual constituents of the compounds considered. Large magneto-optical effects have been predicted for a series of oxides which may find application in magneto-optical hard-drives in computers for data-storage purposes.

Kontaktperson

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