  Ferroelectric domains are mesoscale structures that mediate between
synchronized atomic-scale ion displacements and switchable macroscopic
polarization. Here, we evaluated the randomness of the domain distribution at
the onset of ferroelectricity. First-principle calculations combined with
atomic-scale imaging demonstrate that oxygen vacancies that serve as pinning
sites for the ferroic domain walls remain immobile above the Curie temperature.
Thus, upon cooling to a ferroelectric state, these oxygen vacancies dictate
reproducible domain-wall patterning. Domain-scale imaging with
variable-temperature piezoresponse force microscopy confirmed the memory
effect, questioning the spontaneity of domain distribution under thermotropic
transitions.
