Ultrathin Non‐Ising Charged Domain Walls Confined in BiFeO3 Nanocrystals

Rich functionalities have been identified for domain walls (DWs, naturally occurring interfaces in ferroics), e.g., enhanced conductance and photovoltaic effect, which specify the interest in their internal structure. The dimension/width and type are of particular interest, which is the carrier of their functionality. Recent attention has been focused on head‐to‐head or tail‐to‐tail charged DWs with greatly enhanced conductivity compared to the inner domains, which are found to be an order of magnitude thicker (tens of unit cells) than normal neutral DWs. In this study, ultrathin non‐Ising charged DWs are found, where polarization switched their direction within 2–3 unit cells in self‐assembled BiFeO3 nanocrystals. An analytical model and finite element method simulation are used to interpret the origin of this phenomenon, i.e., electrostatic constraints linked to DW configurations in a ferroelectric. This study indicates that as an intrinsic property, the width of the ferroic DWs varies with different electrostatic constraints and must be taken into consideration during its applications. In this work, ultrathin non‐Ising charged domain walls (DWs) where polarization switches direction within 2‐3 unit cells in BiFeO3 are found. This deepens previous understanding that charged DWs are normally an order of magnitude thicker than neutral ones. An analytical model is used to interpret this phenomenon origin, i.e., electrostatic constraints linked to DW configurations in a ferroelectric.