Scattering properties of ferroelectric domain walls

Ferroelectric domain walls have recently been considered as candidates for the occurrence of non-linear (soliton) excitations and roughening transitions. By means of X-ray or neutron scattering experiments, the domain walls may be observed directly and their width may be measured. The occurrence of a roughening transition would be observable by these techniques, and the roughening mechanism is suggested as an explanation of existing experimental results for Pb 5 Ge 3 O 11 . A neutron scattering study of the domain walls in deuterated KH 2 PO 4 is described. The domain walls in this system are shown to have a width of around two unit cells. This result implies that the continuum approximation used to describe nonlinear excitations in systems with domain walls is not applicable to KH 2 PO 4 , and quite probably to many other systems.