INVESTIGADORES
DALOSTO sergio Daniel
artículos
Título:
Strain-gradient-induced switching of nanoscale domains in free-standing ultrathin films
Autor/es:
BELLETTI, GUSTAVO; DALOSTO, S; TINTE, SILVIA
Revista:
PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS
Editorial:
American Physical Society
Referencias:
Año: 2014 vol. 89 p. 174104 - 174104
ISSN:
0163-1829
Resumen:
We report first-principle atomistic simulations of the effect of local strain gradients on the nanoscale domain morphology of free-standing PbTiO3 ultrathin films. First, the ferroelectric properties of free films at the atomic level are reviewed. For the explored thicknesses (10 to 23 unit cells), we find flux-closure domain structures whose morphology is thickness dependent. A critical value of 20 unit cells is observed: thinner films show structures with 90◦ domain loops, whereas thicker ones develop, in addition, 180◦ domain walls, giving rise to structures of the Landau-Lifshitz type. When a local and compressive strain gradient at the top surface is imposed, the gradient is able to switch the polarization of the downward domains, but not to the opposite ones. The evolutionof the domain pattern as a function of the strain gradient strength consequently depends on the film thickness.Our simulations indicate that in thinner films, first the 90◦ domain loops migrate towards the strain-gradient region, and then the polarization in that zone is gradually switched. In thicker films, instead, the switching in the strain-gradient region is progressive, not involving domain-wall motion, which is attributed to less mobile 180◦ domain walls. The ferroelectric switching is understood based on the knowledge of the local atomic properties, and the results confirm that mechanical flexoelectricity provides a means to control the nanodomain pattern in ferroelectric systems.