Domain wall conduction in bismuth ferrite

Ferroelectric bismuth ferrite has been extensively studied as a candidate material for high-temperature piezoelectric devices. One of the drawbacks of this material is its high electrical conductivity which mostly stems from the local conduction at the domain walls. Mobile charged defects, accumulated at the domain walls to screen polarization charges, have been proposed in several ferroelectrics as the origin of this local conduction, however, the presence of defects has not yet been directly confirmed. Using state-of-the-art aberration corrected electron microscopy, we explained the p-type conduction mechanism at the domain walls of bismuth ferrite and thus contributed the missing piece for explaining domain-wall conduction in ferroelectrics. We elaborated two analytical methods allowing chemical analysis at the atomic scale, which lead to identification of iron (IV) ions and bismuth vacancies accumulated at the domain walls. Iron (IV) ions in bismuth ferrite are associated with electron holes, thus leading to p-type hopping conduction at the domain walls. We further showed that the local domain-wall conductivity can be tailored by controlling the atmosphere during high-temperature annealing. The results open up possibilities for engineering local conductivity in ferroelectrics thus advancing the development of ferroelectric materials for sensors, actuators, ultrasound transducers and even nanoelectronics.