Volume 89, Issue 5, 01 March 2001
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
89(2001); http://dx.doi.org/10.1063/1.1339207View Description Hide Description
The leakage current density–applied field characteristics of (BSTO) thin film capacitors with Pt electrodes that have been annealed in forming gas (95% Ar 5% or were investigated over the temperature range from −60 to +60 °C. Forming gas annealing significantly increased the leakage current density. The characteristics exhibited features that could not be fully explained by either a simple thermionic emission or tunneling (Fowler–Nordeim) formalism. Using the general charge transport theory of Murphy and Good, we show that the characteristics can be successfully interpreted in terms of tunneling of electrons through the interfacial Schottky barrier with the peak in energy distribution of the incident carriers strongly dependent on applied field. At high applied fields the energy distribution of incident carriers is peaked near the Fermi level in the electron injecting metal electrode at all temperatures considered in this study, leading to almost temperature independent characteristics. At lower applied fields the peak in energy distribution shifts towards the conduction band edge where thermally assisted tunneling occurs and a more pronounced temperature dependence of the current density is observed. Good agreement between experiment and theory is demonstrated for a reasonable parameter set for BSTO thin films strongly suggesting that the high leakage current density often observed after forming gas annealing results from tunneling of electrons through the interfacial Schottky barrier.
89(2001); http://dx.doi.org/10.1063/1.1345517View Description Hide Description
The theory of shear horizontal wave scattering processes in layered piezoelectriccomposites is discussed in terms of a recursive system of equations involving the piezoelectric impedance. Piezoelectric materials of hexagonal 6 mm symmetry are considered. The behavior of an incident shear horizontal piezoelectricwave is analyzed as a function of the material properties, layer thicknesses, and frequency (ω). By an appropriate choice of the materials and layer thicknesses, frequencies at which almost all energy is transmitted can be found, optimizing the properties of the system for ultrasound transducers. This behavior is also dependent on the incident angle. Furthermore, most laminated materials are bonded using polymers. We show that adding these polymers hampers the response of the piezoelectric laminated system, localizing the transmission at particular incident angles. Thus, sharp spikes of ultrasonic pulses could be generated with these laminated structures.
89(2001); http://dx.doi.org/10.1063/1.1337595View Description Hide Description
We study the viscoelectroelastic behavior of heterogeneous piezoelectric solids, focusing on the connection between heterogeneity and coupled mechanical and electrical relaxations. Our approach is based on the existence of a correspondence between quasistatic viscoelectroelasticity and static piezoelectricity when linear constitutive response exists. We couple this correspondence principle with micromechanics models to predict the overall behavior of heterogeneous piezoelectric solids in terms of microstructural details. We devote specific attention to a class of two-phase materials consisting of a lossless piezoelectric phase embedded in a lossy (mechanically and electrically) matrix and obtain closed form expressions for the effective complex electroelastic moduli. Numerical results are presented and discussed, and qualitative agreement with experiment is observed.