Influence of the growth direction on properties of ferroelectric ultrathin films

Abstract

A first-principles-based approach is developed and used to investigate Pb͑Zr 0.4 Ti 0.6 ͒O 3 ultrathin films having different growth directions and subject to different boundary conditions. A wide variety of dipole patterns is found, including ferroelectric phases absent in the bulk and different periodic stripe nanodomains. Moreover, a large enhancement of dielectricity is found in ultrathin films exhibiting a growth direction that differs from a possible direction of the polarization in the corresponding bulk. A set of two general and simple rules is provided to analyze and understand all these features.

Domain evolution ofBaTiO3ultrathin films under an electric field: A first-principles study

“…It is predicted that, under zero field, such stripes alternate along [1][2][3][4][5][6][7][8][9][10] I II III IV I II III IV I II III IV I II III IV …”

“…Note that the stripe to bubble domain transition is numerically found for E z in between 41×10 7 and 45×10 7 V/m (because of the zigzagged domain walls, it is difficult to exactly pin point the onset of stripe to bubble domain transition, unlike in PZT thin films [9]). Once the nanobubbles are formed, they dramatically contract along [110] while keeping their width along [1][2][3][4][5][6][7][8][9][10] more or less the same under further applied field − as seen in Figs. 1d and 1e.…”

“…[2][3][4][5][6][7][8][9][10][11][12] Interestingly, the morphology of such nanostripe patterns seem to dramatically depend on the materials, as suggested by the facts that 180 o nanostripes are known to alternate along the [010] direction in (001) Pb(Zr,Ti)O 3 (PZT) and PbTiO 3 thin films [5,6,[9][10][11] while Ref. 4 predicts that such stripes alternate along another direction (namely, along [1][2][3][4][5][6][7][8][9][10]) in (001) BaTiO 3 (BTO) ultrathin films. The exact reason behind such difference, that is reminiscent of distinct behaviors found in Pb-versus Ba-based alloys, [13,14] remains to be addressed.…”

“…1d and 1e. In other words, as in PZT films, [9] the bubbles contract parallely to the direction along which the initial stripe domains were running (i.e., [110] in BTO versus [100] in PZT films) while keeping their width fixed parallel to the direction along which the initial stripe domains were alternating (i.e., [1][2][3][4][5][6][7][8][9][10] …”

Strain on ferroelectric thin films

“…In addition, no firstprinciple based calculations results have been published so far on anisotropic biaxial misfit strain phase diagrams. The influence of different growth directions has indeed already been considered [186], but the strain field applied on the material was taken as isotropic. These calculations, though computer-wise intensive, would provide the community with predictive tools for reduced-size device design.…”