Domain formation and strain relaxation in epitaxial ferroelectric heterostructures

Abstract

The growth of PbTi03 films by a metalorganic chemical-vapor-deposition technique has resulted in three-dimensionally epitaxial heterostructures on various single-crystal substrates. These heterostructures consist of PbTi03 films on the (001) surface of the single crystals: potassium tantalate (KTa03), strontium titanate (SrTi03), and magnesium oxide (MgO). It was found that the presence of a structural (ferroelectric) phase transition in PbTi03 leads to a "strain-accommodating" mechanism in which a domain pattern forms as the system cools through the Curie temperature and limits the extension of interfacial strain in the heterostructurethus minimizing the total energy of the heterostructure. ForPbTi03/KTa03 (001), the interfacial strain is accommodated by the formation of a periodic domain pattern in the overlayer. In PbTi03/Sr Ti03 (001), which exhibits an excellent lattice match between respective a lattice parameters, the film exists as a single c domain. The PbTi03/MgO(001) system, having a poor lattice match for both the a and c axes, appears to find the energy minimum by locking into domains of two-dimensional superlattices with the greatest atomic coincidences. It is found that the nature of the domain pattern depends very strongly on both the film thickness and measuring temperature.A theoretical model of the domain-pattern formation has been developed by using linear-elasticity theory and a Landau-Ginzburg-Devonshire-type phenomenological theory for the substrate and the overlayer, respectively. The theoretical predictions and the experimental measurements were in good agreement in both the thickness and temperature dependence of the relative domain population and the spontaneous strains.

Strain on ferroelectric thin films

“…on the cooling pace [77] or on oxygen partial pressure for pulsed laser deposited films [78]. If an increase of a c with thickness has been reported [79], most the experiments tend to show that a c decreases with thickness [76,80,81]; On the contrary, its evolution with temperature makes a consensus: the decrease of a c with temperature has been observed [74,79,82,83] as well as calculated [84,82]. Roytburd and Alpay, in a series of seminal papers [85][86][87], have calculated domain stability maps that indicate the stable phase as a function of the tetragonality of the film and of the relative difference between the substrate and the film's in-plane lattice constants.…”

“…One then gets four peaks, separated by p/2, corresponding to the fourfold symmetry of the substrate and a set of four other peaks, at the same / values, equally spaced over 2p. In the case of PbTiO 3 deposited on MgO, another orientation is possible [80]. Indeed the film may be rotated by p/4 with respect to the substrate's axes, in order to minimize the elastic strain due to the lattice mismatch.…”

Domain switching energies: Mechanical versus electrical loading in La-doped bismuth ferrite–lead titanate

“…23 The influence of mechanical load is not limited to external stress; intrinsic internal stress has also been found to influence the switching behavior of ferroelectric materials. 24,25 If the distortion is too large, the internal stress can suppress switching and prevent poling.…”

Cooperative Jahn-Teller transition and resonant x-ray scattering in thin filmLaMnO3

“…Clearly this is the result of the effort of the system which tried to reduce the strain energy as much as possible when the system underwent the transition from a pseudocubic to orthorhombic phase. Domain formation is often found in a thin film which undergoes a structural change [16]. The difference between the two domains lies in their relative orientation, and we focus on the A domain only.…”