Origin of Ferroelastic Domains in Free-Standing Single Crystal Ferroelectric Films

TL;DR

This paper presents a model explaining the formation of 90° ferroelectric/ferroelastic domains in free-standing BaTiO3 crystals, attributing their origin to surface tension effects rather than physical damage, with implications for nanoscale ferroelectric materials.

Contribution

The study introduces a model linking domain formation to surface tension effects, providing a new understanding of domain origins in free-standing ferroelectric crystals.

Findings

Domains form due to elastic stress from a surface layer.

Surface tension effects are significant at small dimensions.

Domain configuration persists after removing physical damage.

Abstract

The origin of the unusual 90^o ferroelectric / ferroelastic domains, consistently observed in recent studies on meso and nanoscale free-standing single crystals of BaTiO3 [Schilling et al., Physical Review B, 74, 024115 (2006); Schilling et al., Nano Letters, 7, 3787 (2007)], has been considered. A model has been developed which postulates that the domains form as a response to elastic stress induced by a surface layer which does not undergo the paraelectric-ferroelectric, cubic-tetragonal phase transition. This model was found to accurately account for the changes in domain periodicity as a function of size that had been observed experimentally. The physical origin of the surface layer might readily be associated with patterning damage, seen in experiment; however, when all evidence of physical damage is removed from the BaTiO3 surfaces by thermal annealing, the domain configuration remains practically unchanged. This suggests a more intrinsic origin, such as the increased importance of surface tension at small dimensions. The effect of surface tension is also shown to be proportional to the difference in hardness between the surface and the interior of the ferroelectric. The present model for surface tension induced twinning should also be relevant for finely grained or core-shell structured ceramics.