Charge and polarization distributions at the 90° domain wall in barium titanate ferroelectric

The authors use the PQEq force field based on quantum mechanics studies to provide a first-principles description of the 90° domain wall in barium titanate. Using periodic cells with lengths of up to 74 nm (5120 atoms), the authors find that the domain wall thickness is 21 nm in which the polarization switches over a 5 nm central layer surrounded by two transition layers each 8 nm wide. The central 5 nm layer consists of a 2 nm sublayer with overshooting polarizations and a 3 nm sublayer with reversed polarization. This structure explains the discrepancies in previous analyses, which have suggested domain walls ranging from 100 nm to 1 nm. These results should be of particular importance in developing nanoscale ferroelectric devices.