Investigateion of electronic functions of transition metal oxynitrides

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High quality crystals of transition metal oxynitrides were synthesized in epitaxial thin film forms by nitrogen-plasma assisted pulsed laser deposition. As a result, (1) we found that perovskite SrTaO2N thin film grown under compressive epitaxial strain consisted of small ferroelectric domains and relaxor ferroelectric-like matrix region. DFT calculation suggested that these properties are related with trans- and cis- arrangement of oxygen and nitrogen in TaX6 octahedra, respectively. (2) We controlled the electrical conductivity of SrTaO2N and anatase TaON thin films from insulator to degenerated semiconductor by introducing anion vacancies as electron donor. (3) We succeeded in synthesizing ferromagnetic La0.75Sr0.25MnO3-xNx by solid phase epitaxy method with higher Curie temperature than than the oxide thin film. These results indicated that transition metal oxynitrides are a promissing materials for electronic or magnetic application.