PbTiO3 Epitaxial Films Research Articles

Monoclinic distortion in strain relaxed [111] PbTiO3 epitaxial films

Stabilization of monoclinic distortion in [111]-oriented strained and strain-relaxed PbTiO3 epitaxial films are investigated using a phenomenological model. Under the effect of biaxial strain due to SrTiO3, temperature stability of monoclinic structure induced by vertical compressive stress is investigated. Due to relaxation of substrate constraint in-plane misfit of the epitaxial system changes from isotropic to anisotropic. Strain relaxation mediated formation of monoclinic structure, polarization, volume and shear strain, and dielectric and piezoelectric constants are investigated and compared with experimental data in the literature. For anisotropically strained [111] epitaxial films mechanical boundary conditions that facilitate enhancement of physical constants are explored.

Strain Engineering of Domain Coexistence in Epitaxial Lead-Titanite Thin Films

Phase and domain structures in ferroelectric materials play a vital role in determining their dielectric and piezoelectric properties. Ferroelectric thin films with coexisting multiple domains or phases often have fascinating high sensitivity and ultrahigh physical properties. However, the control of the coexisting multiple domains is still challenging, thus necessitating the theoretical prediction. Here, we studied the phase coexistence and the domain morphology of PbTiO3 epitaxial films by using a Landau–Devonshire phenomenological model and canonic statistical method. Results show that PbTiO3 films can exist in multiple domain structures that can be diversified by the substrates with different misfit strains. Experimental results for PbTiO3 epitaxial films on different substrates are in good accordance with the theoretical prediction, which shows an alternative way for further manipulation of the ferroelectric domain structures.

Depolarization-mediated monoclinic states in ultrathin [111] PbTiO3 epitaxial films

Stress-depolarization field phase stability map is constructed for ultrathin [111]-PbTiO3 epitaxial films coherently grown on SrTiO3. Despite a large compressive strain imposed by the substrate, rhombohedral to monoclinic transition can be induced so that the polarization vector is confined in a symmetry plane. We investigate competition of phase stability and evolution of monoclinic states by inspecting the flattened energy surface, and show that in the presence of depolarization field the critical stress for inducing low-symmetry states can be remarkably lowered. The influence of vertical stress and depolarization field on polarization, monoclinic shear strain, and volume change of unit cell are calculated for the coherent [111]-PbTiO3, and boundary conditions allowing for considerable enhancement in dielectric and piezoelectric responses are revealed.

Ordered 180° ferroelectric domains in epitaxial submicron structures

Large range ordered La0.7Sr0.3MnO3 and SrRuO3 epitaxial dots were fabricated by pulsed laser deposition using stencil masks and were embedded in ferroelectric PbTiO3 epitaxial films. PbTiO3 films grown on top of La0.7Sr0.3MnO3 dots form arrays of 180° domains that are switchable and have good ferroelectric properties. PbTiO3 films made on top of SrRuO3 dots have a monodomain polarization state. These observations point out the importance of the electronic properties of the bottom electrode in the selection of a preferential polarization state in epitaxial ferroelectric films and propose a route of fabricating large arrays of switchable 180° ferroelectric domains.

Surface passivation and electronic structure characterization of PbTiO3 thin films and Pt∕PbTiO3 interfaces

The surface electronic structure, postdeposition surface passivation, and Schottky barrier height in contact with Pt of PbTiO3 thin films on (001) SrTiO3 were investigated by x-ray photoemission spectroscopy (XPS). Angle-resolved XPS analysis shows that an ∼10-Å-thick surface layer which consists of lead carbonate and lead oxide exists on high-quality PbTiO3 epitaxial films, although the layer can be removed by postdeposition aqueous HNO3 etching. Electronic states associated with this defective surface layer determine the position of the surface Fermi level relative to the band edges of the PbTiO3 film. In situ XPS measurements were carried out during the Pt deposition on as-grown and HNO3-treated PbTiO3 films. The Pb 4f, Ti 2p, and O 1s peaks were observed to shift to higher binding energies during the in situ Pt deposition, consistent with metallization-induced band bending. Although the initial Fermi energies for both Pt-uncoated as-grown and HNO3-treated PbTiO3 differ by ∼0.3eV, the postmetallization Fermi energy lies at 2.4eV above the valence-band maximum after 2 ML (monolayers) of the Pt deposition for both samples. These results suggest that the Fermi level is pinned by interface defect states because the resulting Pt∕PbTiO3 electron Schottky barrier (∼1eV) is substantially smaller than the value derived from recent electronic structure calculations (1.45eV). Consistent with this observation, angle-resolved XPS results indicate that the (001) surface of both as-deposited and HNO3-treated PbTiO3 films decomposes during the initial stages of the Pt deposition and that metallic Pb diffuses into the Pt layer during the Pt deposition, even at room temperature. The presence of the metallic Pb and the resultant formation of a defective interface layer at the Pt∕PbTiO3 (001) interface apparently produce the observed Fermi energy pinning.

Dielectric, ferroelectric, and piezoelectric properties of (001) BiScO3–PbTiO3 epitaxial films near the morphotropic phase boundary

Dielectric, ferroelectric, and piezoelectric properties of (001) BiScO3–PbTiO3 epitaxial films near the morphotropic phase boundary

Dielectric, ferroelectric, and piezoelectric properties of (001) BiScO3–PbTiO3 epitaxial films near the morphotropic phase boundary

The dielectric, ferroelectric, and piezoelectric properties of (001) BiScO3–PbTiO3 epitaxial films near the morphotropic phase boundary were investigated. Epitaxial films, 1-μm thick, were grown on (100) SrRuO3/(100) LaAlO3 substrates by pulsed laser deposition from a BiScO3–PbTiO3 (40/60) ceramic target. The films had room temperature dielectric constant of 850, tanδ = 0.08, and maximum dielectric constant of 5530 at 455 °C. Well-saturated hysteresis loops with a remanent polarization of 42 μC/cm2 and a coercive field of 75 kV/cm were observed. The effective transverse piezoelectric coefficient e31,f was −12 C/m2. This result is quite encouraging for sensor and actuator device development because the observed piezoelectric properties are as good as (001) oriented Pb(Zr,Ti)O3 films (e31,f ∼ –12 C/m2) while the transition temperature is 100 °C higher.

Growth and properties of (001) BiScO3–PbTiO3 epitaxial films

The ferroelectric and piezoelectric properties of (001) BiScO3–PbTiO3 epitaxial films were investigated. Epitaxial films 1 μm thick were grown by pulsed laser deposition using ceramic targets of (1−x)BiScO3–xPbTiO3 (x=0.5) at substrate temperatures of 700 °C on (100) SrRuO3/(100)LaAlO3 substrates. Well-saturated hysteresis loops with a remanent polarization of 36 μC/cm2 were observed. The films had a room temperature dielectric constant of 800, tan δ=0.09 and a maximum permittivity of 3600 at 460 °C. The room temperature e31f piezoelectric coefficient was −9 C/m2. The piezoelectric properties obtained were comparable to those of Pb(Zr,Ti)O3 or relaxor ferroelectric-PbTiO3 films.

C-Axis Oriented PbTiO 3 Thin Films on MgO and Their Microstructure

PbTiO3 thin films were prepared on MgO(100) substrates using a conventional rf magnetron sputtering system with a powder target. By optimizing the deposition conditions, highly c-axis oriented PbTiO3 epitaxial films were obtained. The c-axes of the domains in the films were normal to the substrate, but some a-axes were tilted from the normal towards <100> directions with a particular angle and fourfold symmetry. From the tilt angle and the tilt directions, it is concluded that 90° domain structures were formed by twins, the domain walls of which were {101} twin boundaries.