Long-range strains and the effects of applied field at 180° ferroelectric domain walls in lithium niobate

Ferroelectric domains with antiparallel polarization are readily induced in congruent ${\mathrm{LiNbO}}_{3}$ with electric fields above 240 kV/cm at room temperature. Even in the absence of external fields, these 180\ifmmode^\circ\else\textdegree\fi{} walls exhibit wide regions of shear strain, on the order of ${10}^{\ensuremath{-}5},$ within a 10-\ensuremath{\mu}m range of the domain walls. Using x-ray topography on samples while applying electric fields of 0--90 kV/cm, we have observed large-scale reversible domain changes. A detailed strain analysis of the piezoelectric behavior at the domain walls, as well as within the domains, indicates that substantial surface displacement is associated with the high contrast of ferroelectric domains in x-ray topographs. These observations show that long-range strain interactions due to applied fields are present around domain walls long before permanent changes are induced.