Effects of anisotropic elasticity in the problem of domain formation and stability of monodomain state in ferroelectric films

TL;DR

This paper analytically investigates how elastic anisotropy influences domain formation and stability in ferroelectric films, revealing conditions for stripe or checkerboard domains and implications for memory device stability.

Contribution

It provides an analytical framework incorporating elastic anisotropy and electrostriction effects, advancing understanding of domain structures and stability in ferroelectric thin films.

Findings

Elastic anisotropy determines domain boundary orientation.

Inhomogeneous strains can stabilize the single domain state.

Checkerboard domains may form under specific conditions.

Abstract

We study cubic ferroelectrics films that become uniaxial with a polar axis perpendicular to the film because of a misfit strain due to a substrate. The main present result is the analytical account for the elastic anisotropy as well as the anisotropy of the electrostriction. They define, in particular, an orientation of the domain boundaries and stabilizing or destabilizing effect of inhomogeneous elastic strains on the single domain state. We apply the general results to perovskite systems like BaTiO3/SrRuO3/SrTiO3 films and find that at least not far from the ferroelectric phase transition the equilibrium domain structure consists of the stripes along the cubic axes or at 45 degrees to them. We have also showed that in this system the inhomogeneous strains increase stability with regards to the small fluctuations of the metastable single domain state, which may exist not very close to the ferroelectric transition. The latter analytical result is in qualitative agreement with the numerical result by Pertsev and Kohlstedt [Phys. Rev. Lett. 98, 257603 (2007)], but we show that the effect is much smaller than those authors claim. We have found also that under certain conditions on the material constants, which are not satisfied in the perovskites but are not forbidden either, a checkerboard domain structure can be realized instead of the stripe-like one and that the polarization-strain coupling decreases stability of a single domain state instead of increasing it. The single domain state is metastable at certain large thicknesses and becomes suitable for memory applications at even larger thicknesses when the lifetime of the metastable state becomes sufficiently large.