Bloch-type domain walls in rhombohedral BaTiO 3

Le résumé fourni par la source

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 BaTiO${}_{3}$. The mechanically compatible and electrically neutral FDWs in rhombohedral BaTiO${}_{3}$ are of 71${}^{\ensuremath{\circ}}$, 109${}^{\ensuremath{\circ}}$, and 180${}^{\ensuremath{\circ}}$ 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${}^{\ensuremath{\circ}}$ FDW and the Bloch nature of the 180${}^{\ensuremath{\circ}}$ FDW, and predict both Ising-type and Bloch-type FDWs are possible for the 109${}^{\ensuremath{\circ}}$ case. Considering the relatively small rhombohedral strain in BaTiO${}_{3}$, 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.

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