Very large dielectric response of thin ferroelectric films with the dead layers

We study the dielectric response of ferroelectric (FE) thin films with "dead" dielectric layer at the interface with electrodes. The domain structure inevitably forms in the FE film in presence of the dead layer. As a result, the effective dielectric constant of the capacitor $\epsilon_{eff}$ increases abruptly when the dead layer is thin and, consequently, the pattern of 180-degree domains becomes "soft". We compare the exact results for this problem with the description in terms of a popular "capacitor" model, which is shown to give qualitatively incorrect results. We relate the present results to fatigue observed in thin ferroelectric films.Comment: 5 pages, REVTeX 3.1 with one eps-figure. A note added that the linear response is not changed by electromechanical effect. To appear in Phys. Rev.

Matching and surface barrier effects of the flux-line lattice in superconducting films and multilayers.

The flux-line lattice dissipation and the pinning force of Bi2Sr2CaCu2O8 and YBa2Cu3O7 films and a Nb/Cu multilayer are investigated with the vibrating reed technique. In magnetic fields oriented under a small angle with respect to the film surfaces the Bi-2:2:1:2 film shows a series of pronounced dissipation maxima at matching fields BN in the irreversible region of the magnetic phase diagram. The Y-1:2:3 film shows tiny damping maxima, whereas no structure in the dissipation of the Nb/Cu multilayer is detected below the upper critical field. The comparison of the matching fields to an anisotropic London model shows that the dissipation maxima are caused by rearrangements of the flux-line lattice configuration due to interactions with the sample surface. The different behavior of the high-temperature superconductors and the Nb/Cu multilayer is understood by explicitly taking the surface barrier into account. Deviations from the surface induced commensurability of the flux-line lattice due to the intrinsic pinning are discussed. Our results indicate that pancake vortices in the Bi-2:2:1:2 film should be coupled below the irreversibility line and below magnetic fields B??0.5 T perpendicular to the film surface

Phenomenological description of phase transitions in thin BaTiO3 films

Phase transitions in thin epitaxial films of BaTiO3 are described phenomenologically in terms of Landau potentials with sixth-and eighth-order terms. It is established that the phase diagram depends on the electrostrictive constant Q 12. The phase diagrams calculated for different values of Q 12 available in the literature differ qualitatively. The dependence of the misfit strain of a film on the film tetragonality at room temperature is found, which makes it possible to determine the thermodynamic path in the phase diagram for a specific film. The dependences of the spontaneous polarization and dielectric constant of a film on the misfit strain at room temperature are constructed. © 2008 Pleiades Publishing, Ltd

Molecular dynamics of C70S48: Dielectric function and NMR study

Molecular dynamics of C70S48 have been studied by dielectric relaxation spectroscopy and NMR. In accordance with the NMR data, the rotation of C70 molecules is not hindered by sulfur, and even at room temperature, it is uniaxial like that in pure C70. Numerous phase transitions observed for pure C70 have no analogues in E70S48. The only anomaly of the dielectric function was found at 245 K. In accordance with the NMR data, C70 molecules rotate uniaxially at room temperature, but below 170 K, this rotation begins to freeze, and at 150 K, the rotation is frozen in the NMR scale. Dielectric function temperature dependence does not show any anomalies around 170 K, where the NMR registered a freezing of the rotational freedom of C70 molecules, and the NMR does not show any features around 245 K, where the dielectric function shows a sharp anomaly. Some possible explanations for the nature of the anomaly around 245 K are discussed. © 2001 American Chemical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Features of Phase Transitions in Nanostructured Ferroelectric Oxides Revealed from Calorimetric Data

A short review of the study of thermal properties of the nanostructured ferroelectrics is given. An application of the modern calorimetric technique to a comparative study of phase transitions in the ferroelectric nanostructured materials (polycrystalline and epitaxial thin films, superstructures, ferroelectric heterostructures, substrate-induced ferroelectricity) is considered.