Department of Physics, Kyungpook National University
경북대학교 물리학과

KNU Physics Colloquium Series

Emergent Functionalities on Transition Metal Oxide Heterostructures

by Prof. Kyung-Tae Kang (Kyungpook National University)

120호 (제1과학관)




Designing transition metal oxide heterostructure is like ‘a LEGO brick play’ using atom pieces. One with many atomic LEGO pieces, including oxygen, can construct an oxide heterostructure on her/his hands. Due to diverse parameters such as transition metals of multivalence, epitaxial strain, and stoichiometry, the oxide heterostructure has shown intriguing properties for  fundamental physics on top of applications. Significantly, the development  of the growth methodology of pulsed laser deposition (PLD) helps us precisely  engineer the nano-to-macro structure of oxide heterostructures. 

Here, we introduce a variety of emergent functionalities in transition metal   oxide heterostructure. First, we report a nano-scale real-time observation of oxygen vacancy-driven topotactic phase transformation from the perovskite  SrFeO3 to brownmillierite SrFeO2.5. Topotactic phase transformation provides avenues for understanding and tailoring important functionalities across multiple disciplines, including electrochemical activities, structural symmetry modification, and metal-to-insulator transition. However, direct real-time atomic-scale imaging has not been possible so far. Oxygen vacancy formation, migration, and order during the PV-to-BM transformation were studied through quantitative analyses of oxygen intensity and cation sublattice movement at the atomic scale. Our real-time high-resolution transmission electron microscopy (HRTEM) movie, in conjunction with density functional theory (DFT) calculation, unravels the oxygen migration pathway responsible for the collective lattice dynamic motion.

Second, we investigated the emergent functionalities in the exotic structure  of freestanding oxide membranes, in which room-temperature ferroelectricity or ferromagnetism arises. BaTiO3/La0.7Sr0.3MnO3 bilayer and CoFe2O4 membranes fabricated by using pulsed laser epitaxy have been utilized to look into the effect of various strain environments, from non-strained to massive bending, on the emergent ferroelectricity and ferromagnetism. 

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