Local electromechanical properties of the polycrystalline BiFeO3 thin films: collective polarization and transport phenomena

Abstract

Charge transport across the interfaces in complex oxides attracts a lot of attention because it allows the creating of novel functionalities. The movable domain walls in epitaxial BiFeO3 films possess enhanced conductivity that can be used for reading out in ferroelectric-based memories [1]. Chemical solution deposition of BiFeO3 thin films is one of the most commercially available techniques to produce large-scale low-cost coatings for application in memory devices. In this work, complementary piezoresponse force microscopy, conductive atomic force microscopy, and electron backscattered diffraction methods are used to study the local phase distribution, morphology, piezoelectric response, and leakage current of the polycrystalline BiFeO3 thin films. The relation between the polarization, strain, and conductivity in sol-gel BiFeO3 films with special emphasis on grain boundaries as natural interfaces in polycrystalline ferroelectrics is investigated [2]. It was demonstrated that an interaction between the polarization and grain boundaries at elevated temperature leads to the formation of the highly conductive grain boundaries with the electrical conductivity about two orders higher than in the bulk. At room temperature, the conductive traces of the charged defects at the position of the grain boundaries remain and do not change upon polarization switching. These collective states provide further insight into the physics of complex oxide ferroelectrics and strongly affect their practical applications because reveal an additional mechanism of the leakage current in such systems. The research was made possible by Russian Science Foundation (Grant 19-72-10076). The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. [1] J. Seidel et al., “Conduction at domain walls in oxide multiferroics,” Nat. Mater., vol. 8, no. 3, pp. 229–234, Mar. 2009. [2] D. Alikin et al., “Strain-polarization coupling mechanism of enhanced conductivity at the grain boundaries in BiFeO3 thin films,” Appl. Mater. Today, vol. 20, p. 100740, Sep. 2020.