Three-domain architecture of stress-free epitaxial ferroelectric films

Epitaxial ferroelectric films undergoing a cubic-tetragonal phase transform ation relax internal stresses due to the structural phase transformation an d the difference in the thermal expansion coefficients of the film and the substrate by forming polydomain structures. The most commonly observed poly domain structure is the c/a/c/a polytwin which only partially relieves the internal stresses. Relatively thicker films may completely reduce internal stresses if all three variants of the ferroelectric phase are brought toget her such that the film has the same in-plane size as the substrate. In this article, we provide experimental evidence on the formation of the three-do main structure based on transmission electron microscopy in 450 nm thick (0 01) PbZr0.2Ti0.8O3 films on (001) SrTiO3 grown by pulsed laser deposition. X-ray diffraction studies show that the film is fully relaxed. Experimental data is analyzed in terms of a domain stability map. It is shown that the observed structure in epitaxial ferroelectric films is due to the interplay between relaxation by misfit dislocations at the deposition temperature an d relaxation by polydomain formation below the phase transformation tempera ture. (C) 2001 American Institute of Physics.