Domain evolution of BaTiO3 ultrathin films under an electric field:: A first-principles study

A first-principles-derived method is used to study the morphology and electric-field-induced evolution of stripe nanodomains in (001) BaTiO3 (BTO) ultrathin films, and to compare them with those in (001) Pb(Zr,Ti)O-3 (PZT) ultrathin films. The BaTiO3 systems exhibit 180 degrees periodic stripe domains at null electric field, as in PZT ultrathin films. However, the stripes alternate along [1-10] in BTO systems versus [010] in PZT systems, and no in-plane surface dipoles occur in BTO ultrathin films (unlike in PZT materials). Moreover, the evolution of the 180 degrees stripe domains in the BaTiO3 systems, when applying and increasing an electric field along [001], involves four regions: region I for which the magnitude of the down dipoles (i.e., those that are antiparallel to the electric field) is reduced, while the domain walls do not move; region II in which some local down dipoles adjacent to domain walls switch their direction, resulting in zigzagged domain walls-with the overall stripe periodicity being unchanged; region III in which nanobubbles are created, then contract along [110] and finally collapse; and region IV which is associated with a single monodomain. Such evolution differs from that of PZT ultrathin films for which neither region I nor zigzagged domain walls exist, and for which the bubbles contract along [100]. Discussion about such differences is provided.