Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a “stretch” along one of the four 〈111〉 crystallographic directions of the cubic perovskite unit cell. Domain pattern formation is concurrent with the PC→FR transformation on cooling from the growth temperature. The domain patterns form to minimize elastic energy in the film, at the energetic expense of both forming domain boundaries and developing local stresses in the substrate. Eight possible domains may form, half of which are related by inversion, thus leading to four mechanically distinct variants. The possible domain walls are determined by mechanical and charge compatibility and follow closely from the analysis of Fousek and Janovec [J. Appl. Phys. 40, 135 (1969)]. Domain patterns may develop with either {100} or {101} boundaries. In both cases, the individual domains in the patterns are energetically degenerate and thus equal width lamellar patterns are predicted. When polarization is included in the analysis, the {100} boundary patterns have no normal component of the net polarization, whereas the {101} boundary patterns correspond to the fully poled state. We report on experimental observation of {100} domain patterns in epitaxial PbZr0.80Ti0.20O3 and PbZr0.65Ti0.35O3 films.

No abstract

A comprehensive review is given on experimental studies of small particles with fivefold symmetry accompanied by an in-depth theoretical description of their characteristics and computer modeling. The cases of uniform and nonuniform deformations (disclination model), stability and relaxation of elastic stresses in pentagonal particles and needle-like crystals, models of their formation are discussed.

A recently observed mechanism of elastic stress relaxation in mismatched layers is discussed. The relaxation is achieved by the inclination of pure edge threading dislocation lines with respect to the layer surface normal. The relaxation is not assisted by dislocation glide but rather is caused by the ''effective climb'' of edge dislocations. The effective dislocation climb may result from the film growth and it is not necessarily related to bulk diffusion processes. The contribution of the dislocation inclination to strain relaxation has been formulated and the energy release due to the dislocation inclination in mismatched stressed layers has been determined. This mechanism explains recently observed relaxation of compressive stresses in the ͑0001͒ growth of Al x Ga 1Ϫx N layers.