Coercive fields in ferroelectrics: A case study in lithium niobate and lithium tantalate`

The experimentally measured coercive electric fields for domain reversal in ferroelectrics are typically many orders of magnitude lower than the estimates from phenomenological free-energy theory. This letter specifically investigates the influence of polarization gradients at pre-existing 180° domain walls in ferroelectrics on coercive fields for domain wall motion. It is shown that the ratio of theoretical coercive field without and with a preexisting domain wall is directly proportional to the ratio xo /a, where a is the lattice parameter and 2xo is the polarization wall width. This factor is 7.5–45 for a 20–120 nm wall width, the latter width determined here as the experimental upper limit for polarization wall width in lithium tantalate