[Paper Review] Correlation Between Structure and Conductivity of 180-Degree Domain Walls in Ferroelectric BaTi03

Eugene А. Eliseev, P. V. Yudin+4 more|arXiv (Cornell University)|Aug 15, 2012

Nonlocal and gradient elasticity in micro/nano structures3 citations

TL;DR

This study uses Landau-Ginzburg-Devonshire theory to investigate how flexoelectric coupling and domain wall orientation affect the structure, energy, and conductivity of 180° domain walls in n-type rhombohedral BaTiO3. It identifies two distinct wall phases—odd-symmetry near {110} and chiral bistable states near {211}—with the latter showing strong conductivity enhancement due to electric potential variation and free carrier accumulation, leading to conductivity at least one order of magnitude higher than in single-domain regions.

ABSTRACT

Using Landau-Ginzburg-Devonshire theory we self-consistently calculate the influence of the flexoelectric coupling and orientation on the 180-degree domain wall structure, intrinsic energy and static conductivity in rhombohedral phase of n-type BaTiO3. Two types of domain wall structures (phases of the wall) exist depending on the wall orientation. The stable odd phase occurs in the vicinity of the {110} wall orientation and has polarization profile invariant with respect to inversion about the wall center. The second bistable phase occurs around {211} wall orientations and corresponds to mixed parity chiral domain walls that may be switched from the left-handed state to the right-handed one. The transformation between the phases is abrupt and close to the first order. The flexoelectric effect reduces the symmetry of the wall energy angular anisotropy and strongly influences the value and rotation symmetry of the polarization component normal to the wall plane. The component, inherent to the both wall types, causes the depolarization field and electric potential variation across the wall. Electric potential variation leads to free carriers accumulation by the wall. Depending on the temperature and flexoelectric coupling strength the wall static conductivity becomes at least one order higher than in the single-domain region, creating the conductivity enhancement pronounced and easily detectable by current-AFM.

Motivation & Objective

• To understand the influence of flexoelectric coupling and wall orientation on the structure and energy of 180° domain walls in n-type BaTiO3.
• To determine how symmetry breaking via flexoelectric effects alters the polarization profile and electric potential across the domain wall.
• To investigate the static conductivity of domain walls and its dependence on temperature and flexoelectric coupling strength.
• To identify distinct wall phases based on orientation and their transformation behavior.

Proposed method

• Self-consistent calculation using Landau-Ginzburg-Devonshire (LGD) theory to model the free energy of the system.
• Incorporation of flexoelectric coupling to account for strain-induced polarization gradients at the domain wall.
• Analysis of wall energy angular anisotropy and symmetry breaking due to flexoelectric effects.
• Computation of polarization profiles and electric potential variation across the wall to assess depolarization fields.
• Evaluation of free carrier accumulation due to potential gradients and resulting static conductivity.
• Use of current-AFM as a detection method for conductivity enhancement.

Experimental results

Research questions

• RQ1 How does flexoelectric coupling influence the structural and energetic properties of 180° domain walls in BaTiO3?
• RQ2 What are the distinct phases of 180° domain walls, and how do they depend on wall orientation (e.g., {110} vs. {211})?
• RQ3 What is the role of polarization components normal to the wall plane in generating depolarization fields and electric potential variation?
• RQ4 How does the static conductivity of the domain wall compare to that of the single-domain region?
• RQ5 What is the nature of the phase transformation between the odd and chiral wall phases?

Key findings

• Two distinct domain wall phases exist: an odd-symmetry phase near {110} orientations and a bistable chiral phase near {211} orientations.
• The transformation between these phases is abrupt and close to first-order in character.
• Flexoelectric coupling reduces symmetry in wall energy anisotropy and influences the normal polarization component, which generates depolarization fields.
• The normal polarization component causes electric potential variation across the wall, leading to free carrier accumulation.
• Static conductivity in the domain wall is at least one order of magnitude higher than in the single-domain region.
• The conductivity enhancement is pronounced and detectable using current-AFM.