Coexisting Polar and Antipolar BiFeO3 Phases Imaged by Microwave Microscopy*

The dielectric response of ferroelectrics plays an important role in their potential applications. As a model material system, the BiFeO3-TbScO3 (BFO-TSO) superlattices may exhibit coexistence of centrosymmetric (antipolar) and non-centrosymmetric (polar) phases in the BFO layers. Using microwave impedance microscopy (MIM), we quantitatively measured the permittivity and conductivity contrast between the antipolar and polar phases at GHz frequencies. Interestingly, while the antipolar phase remains highly insulating, the polar phase with two orientations of the net polarization displays the semiconducting behavior with a resistivity five orders of magnitude lower than that of the bulk BFO. Moreover, the application of in-plane electric fields can lead to reversible and nonvolatile interconversion between the two phases, which is also imaged by the MIM. Our work shows a unique method to spatially resolve the dielectric and conduction properties in complex ferroelectric structures, which may extend to other materials as well.