BiFeO 3 thin films were fabricated on ͑111͒Pt/Ti/SiO 2 /Si substrates via Bi-acetateand Fe-acetylacetonate-based chemical solution deposition and spin-coating techniques. The processing parameters were optimized in order to obtain films with high resistivity. The optical properties ͑refractive indices and extinction coefficients͒ were measured by means of ellipsometry ͑HeNe laser, = 632.8 Å͒. Microstructure characterization was made by means of atomic force microscopy, grazing incidence x-ray diffractometry ͑XRD͒, and texture analysis. Additionally, powders prepared from a stoichiometric precursor were investigated by means of thermogravimetric and differential thermal analyses and XRD. It is demonstrated that the formation of perovskite-type BiFeO 3 is accompanied by the appearance of bismuth oxide at low temperatures which then transforms into Bi 36 Fe 2 O 57. For the films it was found that annealing in oxygen leads to higher indices of refraction, lower roughness, and smaller grain size. Complete crystallization of the films was achieved at a substantially lower temperature compared to that of the powders. A ͑100͒ ͑pseudocubic͒ out-of-plane preferred orientation was revealed for specimens annealed in air and oxygen. It is supposed that the crystal lattice of the thin film is close to cubic possibly due to stress development at the substrate/film interface. The electrical properties of the films were measured at room temperature by impedance analysis. The piezoelectric properties were determined using a laser vibrometer. Room temperature resistances measured at 1 kHz for metal-film-metal configurations for the specimens annealed in air and O 2 were 14 ⍀ and 1.35 k⍀, respectively. This is explained in terms of the high sensitivity of the oxidation state ͑ϩ2 or ϩ3͒ of iron ions to oxygen stoichiometry in the specimens. Further electrical characterization of the specimen annealed in O 2 revealed very low frequency dispersion of the dielectric constant. A dielectric loss of 1% or less was detected in a wide range of frequency. The films annealed in oxygen showed piezoelectric activity with a value of the piezoelectric coefficient d 33 of 12 pm/V. A relatively weak ferroelectricity ͑remnant polarization 2P r of approximately 1 C/cm 2 ͒ was detected for the specimens annealed in oxygen.

Photosensitive ferroelectric materials exhibit various photoferroelectric phenomena due to the strong influence of nonequilibrium charge carriers on polarization and phase transition. These phenomena are essential for a number of applications including photodriven actuators and sensitive photodetectors. In this work, the effect of UV illumination on dielectric and piezoelectric properties is investigated in lead zirconate titanate (PZT) thin films, which are currently the most promising material for microactuator applications. The effective piezoelectric coefficient (d33) and dielectric permittivity (ε) of PZT films are simultaneously measured under a weak ac electric field during illumination with a band gap light (λ=280–400 nm). It is shown that both d33 and ε decrease under UV illumination. The reduction of permittivity, however, is much smaller than that of d33 and demonstrates a much slower time relaxation. The d33 decrease is attributed to the reduction of average remanent polarization under the UV light. Thus a direct effect of the photoactive light on ferroelectric polarization is observed under essentially nondestructive (weak-field) conditions. The origin of the observed effect is discussed along with the possible implications for thin-film devices.

No abstract

Pb ( Zr , Ti ) O 3 (PZT) thin films were deposited on different substrate heterostructures including platinized silicon, stainless steel and Ni-based alloy foils. A buffer layer of (La0.8Sr0.2)MnO3 (LSMO) between PZT and substrate was used. The pyroelectric coefficients were determined using low frequency sinusoidal temperature waves. It is demonstrated that PZT films deposited on metallic foils exhibit high pyroelectric coefficients of up to 760μC∕Km2 in the unpoled state, whereas the films deposited on platinized substrates were found to have pyroelectric coefficients in the range of 30μC∕Km2. These results are explained in terms of elemental diffusion from the substrate together with stressed states of the films.

Dielectric and ferroelectric properties of sol-gel derived PbTiO3 and (Pb,Er)TiO3 films with thickness in the range from 134 to 420 nm have been investigated. It is demonstrated that 1% Er doping improves the shape of the ferroelectric hysteresis loop probably due to compensation of p-type conductivity. The dielectric constant is shown to be linearly dependent on the amplitude of the measuring signal. It is shown that the Rayleigh equation can be used to discriminate between reversible and irreversible contributions to the dielectric properties of the films. Both reversible and irreversible Rayleigh components were found to be affected by donor doping and film thickness. Introducing 1% of Er is thought to counteract domain wall pinning on “dead layer” near the film–electrode interface.