Bloch-type Domain Walls in Rhombohedral BaTiO3

TL;DR

This study investigates the nature of ferroelectric domain walls in rhombohedral BaTiO3, confirming Ising and Bloch types for specific angles and predicting coexistence of both types at 109 degrees using first-principles and GLD models.

Contribution

It provides a detailed analysis of FDWs in BaTiO3, demonstrating the presence of Bloch-type walls and refining the GLD model parameters for better accuracy.

Findings

71-degree FDW is Ising type

180-degree FDW is Bloch type

Both types possible for 109-degree FDW

Abstract

Ferroelectric domain walls (FDWs) are usually considered to be of Ising type, but there have been suggestions in recent years that Bloch-type FDWs are also possible in some cases, e.g., in the rhombohedral phase of BaTiO3. The mechanically compatible and electrically neutral FDWs in rhombohedral BaTiO3 are of 71-degree, 109-degree, and 180-degree type. We have investigated these FDWs based both on first-principles calculations and on a Ginzburg-Landau-Devonshire (GLD) model [P. Marton, I. Rychetsky, and J. Hlinka, Phys. Rev. B 81, 144125 (2010)]. The results from both approaches confirm the Ising nature of the 71-degree FDW and the Bloch nature of the 180-degree FDW, and predict both Ising-type and Bloch-type FDWs are possible for the 109-degree case. Considering the relatively small rhombohedral strain in BaTiO3, the competition between the energies of Bloch and Ising FDWs can be discussed in terms of a picture in which a Bloch wall is regarded as being composed of a pair of smaller-angle Ising ones. A reduction by 40% in the parameters describing the gradient term in the GLD model brings it into better agreement with the first-principles results for detailed properties such as the energies and widths of the FDWs.