Observation of polar domains in a relaxor La-substituted BiFeO₃ thin film

Relaxor ferroelectrics have been widely studied because of their unique physical properties including high permittivity, high piezoelectric effects, etc. The existence of polar nanoregions (PNRs) is believed to be responsible for relaxor behaviors [1]. However, there is a lack of studies on PNRs linked to the flexoelectric effect. In this work, we report the direct observation of PNRs within tetragonal BiFeO₃ near morphotropic phase boundaries (MPBs) which are expected to involve large strain gradient. Heavily La-substituted BiFeO₃ thin films (BLFO) grown on LaAlO₃ (001) have been employed to explore the PNRs with the aid of an angle-resolved lateral piezoresponse force microscopy [2]. BLFO has been thought to be isotropic monoclinic energies [3]. the flexoelectric effect on tetragonal BLFO near MPBs stabilizes various monoclinic phases. The frequency-dependent dielectric anomalies and diffuse x-ray scattering have been confirmed to identify that our system shows the typical relaxor behaviors. Our findings will offer valuable information to study the role of the flexoelectric effect on the formation of PNRs.
References
[1] L. E. Cross, Ferroelectrics 76, 241 (1987).
[2] K. Chu et al., Rev. Sci. Instrum. 89, 123704 (2018).
[3] B.-K. Jang et al., Nat. Phys. 13, 189-196 (2017).