Exotic closure domains induced by oxygen vacancies in compressed BaTiO3 nanofilm

2020 
The molecular dynamics method based on the shell model is used to investigate the polarization configuration evolution in compressed BaTiO3 nanofilms with oxygen vacancy lattices of different volume fractions and positions. A clockwise closure domain surrounding a head-to-head domain is observed for a single oxygen vacancy nanofilm. With an increasing oxygen vacancy fraction, the closure domain around the vacancy becomes larger and gradually transforms its rotation direction from clockwise to counterclockwise. Inside the vacancy, except for the head-to-head domain remaining unchanged, the domain changes from a random configuration to a clockwise vortex, and finally to a segmented strip polydomain with 90°- and 180°-domain walls. For a single oxygen vacancy, its location region where the closure domain can occur is obtained, and the model center is a favored site for clockwise vortex nucleation. The closure domain partly changes its orientation if the oxygen vacancy shifts off the model center. In addition, homogeneous closure domains can occur when the vacancy changes its location within a small area. This study demonstrates the feasibility of tuning this kind of closure domain in ferroelectric nanofilms through external loadings and oxygen vacancies. This could be instructive to develop novel nanoscale memories and logic devices.
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