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.

TABLE I. Sputtering conditions for BST deposition. Target Ba 0.5 Sr 0.5 TiO 3 Target diameter 3 in. Source to substrate distance 4 in. RF power 90 W Sputtering gas Ar/O 2 ͑sccm͒ Substrate temperature 450-650°C Gas pressure 50 mT Deposition rate 0.4 nm/min

The coherency defect technique is developed for the domain pattern energetics in rhombohedral (001) epitaxial ferroelectric films. The coherency defects that are necessary to maintain the epitaxy during the ferroelectric phase transition are considered to be the only sources of elastic strains and stresses (and, correspondingly energy) in the film/substrate system. The coherency defects include: (i) a uniform distribution of edge dislocations which are responsible for the in-plane tension or compression and have Burgers vectors parallel to the interface; and two kinds of mesoscale defects: (ii) Somigliana screw dislocations which are responsible for in-plane shear; and (iii) wedge disclinations which are responsible for the out of plane rotations in neighboring domains. Using this approach, analytical expressions were found for the elastic energy in the film/substrate system for both the {101}-ri/rj and the {100}-ri/rj domain patterns. These two configurations differ by the orientation of domain walls, coherency defect content, and also the morphology of the free surface (flat versus puckered surfaces). Calculations are performed for screened mesoscale coherency defect configurations that represent a single embedded domain pattern and multidomain patterns. The following mesoscale defect configurations are used for these calculations: Somigliana dislocation dipoles, wedge disclination dipoles, Somigliana dislocation quadrupoles, and disclination quadrupoles. It is predicted that there is no critical thickness for domain pattern formation in rhombohedral ferroelectric epitaxial films. Agreement is shown between experimentally observed domain widths and theoretically predicted values.

The role of precursor stoichiometry and local firing environment on the microstructural development of sol-gel derived lead zirconate titanate (PZT) thin films was investigated. Typically, excess Pb is added to films to compensate for PbO volatilization during heat treatment. Here, it is shown that the use of stoichiometric precursors with either a PbO atmosphere powder or a PbO overcoat during the crystallization heat treatment is an attractive and viable alternative method for control of film stoichiometry. Using these approaches, we have fabricated single phase perovskite thin films with microstructures and electrical properties (Pr ∼ 36 μC/cm2 and Ec ∼ 45 kV /cm) comparable to those of films using optimized solution chemistries and excess Pb additions. The potential advantage of increasing PbO partial pressure, or activity, during firing versus excess Pb additions is discussed from the standpoint of a proposed crystallization scenario based on the kinetic competition between Pb loss and the nucleation and growth rates of the perovskite phase.

The possible domain patterns are developed for (111) oriented epitaxial tetragonal ferroelectric (FT) films. The domain patterns in the film form as the result of phase transition from the paraelectric to ferroelectric state to minimize the elastic energy of the system at the expense of creating of domain boundaries and developing non‐uniform elastic fields near the film/substrate interface. Six possible domain variants may form, half of which are related by the inversion of the polarization vector. The possible domain walls arising between pairs of variants can be derived from the conditions of the mechanical and charge compatibility. These walls are {101} boundaries (pseudocubic indexing) and can either be inclined or normal to film/substrate interface. The domain patterns with inclined boundaries have a flat free film surface and possess non‐zero net polarization in the direction normal to the film surface, i.e., they correspond to the poled film state. The domain patterns with normal boundaries lead to ‘puckering’ of the film surface, simultaneously they are related to the unpoled state of ferroelectric films. The coherency defect technique is developed for domain pattern energetics for (111) oriented FT films. The coherency defects include (i) a cross‐grid of edge dislocations with unbalanced densities (which lead to in‐plane biaxial strain field), (ii) Somigliana screw dislocations (which produce alternating sense of shear in neighboring domains), and (iii) wedge disclinations (which are related to out‐of‐plane rotations in neighboring domains). Analytical calculations of the pattern energy are performed for single embedded domain and multidomain patterns. These calculations are based on the use of screened configurations for representative coherency elements: disclination and Somigliana screw dislocation dipoles and quadrupoles. It is predicted that there is no critical thickness for domain pattern formation in (111) oriented epitaxial tetragonal ferroelectric films. Tiling of different domain patterns in complex mesoscopic structures is also discussed and supported by experimental observations.