|日時||平成27年7月31日(金) 14:00 – 15:00|
|講演者||Woo Seok Choi 氏|
|所属等||Sungkyunkwan University, Assistant Professor|
|タイトル||Defect Engineering in Complex Oxide Thin Films|
Defect engineering in crystals opens new possibilities for discovering novel phenomena and fine-tuning beneficial properties. For perovskite transition metal oxides, however, controlling and understanding the role of the defects have been mainly limited to the oxygen vacancies. In this presentation, we report efficient defect engineering in complex perovskite oxide thin films.
In the first part of my talk, I will report point defect engineering using Pulsed Laser Epitaxy (PLE). In particular, we observed the selective formation of the different types of elemental vacancies and their individual roles in determining the physical properties of perovskite SrTiO3 homotepitaxial thin films. Among various parameters of PLE, we found that laser energy, oxygen partial pressure (P(O2)), and oxygen flow rate play distinct roles in influencing both oxygen and cation stoichiometry. In particular, laser energy was mainly responsible for changing the cation stoichiometry, while oxygen flow rate selectively tuned the oxygen vacancy concentration in SrTiO3 thin films. Moreover, it was found that oxygen vacancy was mainly responsible for the electronic insulator-to-metal transition, but on the contrary to the common belief, did not influence the Sr vacancy induced cubic-to-tetragonal structural transition. The control of multiple phase transitions in complex oxides exploiting selective vacancy engineering provided by PLE opens an unprecedented opportunity for tailoring and understanding the materials properties.
In the second part, I will discuss the role of epitaxial strain as inducing an ordered defect crystal structure. In particular, we show that the ferromagnetic ordering observed in LaCoO3 thin films is related to a lattice modulation due to the epitaxial strain, which results in a locally-ordered atomic structure. An unconventional strain relaxation behavior identified by strip-like lattice modulation pattern was responsible for the non-zero spin ground state [1,2]. We note that the unconventional strain relaxation did not involve any uncontrolled misfit dislocations or other defects. Our study provides a novel route to tailoring the atomic structure and magnetic properties of functional oxide heterostructures by strain, for various applications. In particular, the catalytic activity of LaCoO3 thin films under different strain state has been studied to show the close correlation between the crystal structure and the chemical activity .
 W. S. Choi et al., Nano Lett. 12, 4966 (2012).
 J.-H. Kwon et al., Chem. Mater. 26, 2496 (2014).
 K. A. Stoerzinger et al., J. Phys. Chem. Lett. 6, 487 (2015).
|連絡先||薄膜機能材料研究分野 太田裕道、片瀬貴義 ((内)9432)|
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