Potential and Impedance Imaging of Polycrystalline BiFeO3 Ceramics

Abstract

Electrostatic‐force‐sensitive scanning probe microscopy (SPM) is used to investigate grain boundary behavior in polycrystalline BiFeO3 ceramics. Scanning surface potential microscopy (SSPM) of a laterally biased sample exhibits potential drops due to resistive barriers at the grain boundaries. In this technique, the tips acts as a moving voltage probe detecting local variations of potential associated with the ohmic losses within the grains and at the grain boundaries. An approach for the quantification of grain boundary, grain interior, and contact resistivity from SSPM data is developed. Scanning impedance microscopy (SIM) is used to visualize capacitive barriers at the grain boundaries. In SIM, a dc‐biased tip detects the variations of local potential induced by the lateral ac voltage applied to the sample. Unlike the traditional dc and ac transport measurement, both of these techniques are sensitive to the variation of local potential (SSPM) or local voltage oscillation amplitude and phase (SIM), rather than to current. Therefore, special attention is paid to the relationship between SSPM and SIM images and data obtained from traditional impedance spectroscopy and dc transport measurements. For BiFeO3 ceramics excellent agreement between the local SIM measurements and impedance spectroscopy data are demonstrated.