The interplay of defects and ferroelectricity at the phase boundaries of Ca-substituted super-tetragonal BiFeO3

In ferroelectric materials, oxygen vacancy defects are the important factors in modifying the resistance state [1], phase transition [2], and ferroelectric transition temperature [3]. But still, understanding the relationship between oxygen vacancies and ferroelectric properties is far from complete. Here, we report the interplay of ferroelectric mixed-phase domain structures with oxygen vacancy in a Ca-substituted super-tetragonal BiFeO3 grown on the LAO (001) substrate. Our experiments show piezoresponse force microscopy (PFM) polarization enhancement at the boundary. The relationship between topography and conduction is investigated by conductive atomic force microscopy (CAFM) under sample-biased tip poling. The base material BiFeO3 is a well-known ferroelectric perovskite that can have R, T, and S phases, and their variations [4]. R phase is grown on a substrate with similar lattice parameters such as SrTiO3 and has polarization in the direction. On the other hand, the T phase is grown on a substrate with smaller lattice parameters such as LaAlO3, is highly elongated in the direction with a major polarization direction along pseudocubic [001] and a weak polarization tilting along direction [5-6]. Although our studies are similar to those on R phase Ca-substituted BiFeO3 [7], super-tetragonal Ca-substituted BiFeO3 is a distinct point of this study. The experimental results would help further deepen our understanding of the interaction between oxygen vacancies and ferroelectrics in strained environments.

References

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7. C.-H. Yang et al., Nat. Mater. 8, 485 (2009).