| Perovskite oxides have many applications,since they possess rich physical properties such as superconductivity,ferroelectricity,ferromagnetism and colossal magnetoresistance,et al.These physical properties are often closely related to their internal structures.Therefore,the structural modulation is very important.There are many factors that affect the structure,among which the introduction of oxygen vacancy is a hot topic recentlyWe found experimentally that oxygen vacancy plates can be introduced by changing the growth conditions of bismuth ferrite thin films,and they can change the domain structure of the films.However,the specific mechanism is still unclear.In order to systematically study the influence of oxygen vacancy plate on the domain structure of bismuth ferrite thin films,phase field simulations were performed to reveal the evolution of domain structures with the size and charge density of a single oxygen vacancy plate.It is found that when the area and charge density of the oxygen vacancy plate are small,71° charged domain walls are favored.When they are relatively larger,109° charged domain walls are formed.In another work,we experimentally observed oxygen vacancy plates in lanthanum cobaltite thin films,and found that the arrangement of oxygen vacancy plates was related to the thickness of the films.When the film thickness was less than 5 nm,oxygen vacancy plates were horizontally distributed;when the film thickness was more than 5 nm,they were vertically distributed.The physical mechanism of this phenomenon is studied by first principles calculations.The results show that the arrangement of oxygen vacancy plates is determined by the competition between the surface energy and the bulk energy of the film.When the film is thin,the surface energy dominates,resulting in the horizontal distribution of oxygen vacancy plates.When the film is thick,the bulk energy dominates,resulting in the vertical distribution of oxygen vacancy plates. |
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