Volume 96, Issue 2, 15 July 2004
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
96(2004); http://dx.doi.org/10.1063/1.1760842View Description Hide Description
Changes in structure and phase transition behavior are investigated for two types of La-doped sodiumbismuthtitanateceramics. When A-site vacancies are formed by La incorporation, the phase transition near 200 °C becomes pronounced. Hysteresis loop and demonstrate that the structure above 200 °C is the incommensurate antiferroelectric phase. In contrast, B-site vacancies produced by La doping do not contribute to the incommensurate phase. The origin for the formation of the incommensurate antiferroelectric state between the rhombohedral ferroelectric phase and tetragonal paraelectric phase is discussed in a view of decoupling effects due to the A-site vacancies.
96(2004); http://dx.doi.org/10.1063/1.1759087View Description Hide Description
The global matrix techniques are used in the analysis of the Stark-Ladder resonances for transverse horizontal and surface waves in piezoelectricmultilayers. Stark-Ladder resonances are observed when these waves propagate inside composites consisting of Npiezoelectric layers whose piezoelectricproperties obey a special linear relation. Each layer is made of materials with hexagonal 6 mm symmetry. The resonances are studied through the transmission coefficient. The transmission coefficient shows the well known band structure for a periodic piezocomposite, and when a linear term in the values of the piezoelectric parameters of the layers (which breaks the periodicity) is added, the band structure is destroyed and, in certain cases, resonances of the Stark-Ladder type are shown. The transmission coefficient is studied as a function of the properties of the materials and angle of incidence of the waves. Numerical results for two different configurations of piezocomposites are presented, one of them showing the existence of Stark-Ladders resonances. An analysis of the resonance spectrum is given.
96(2004); http://dx.doi.org/10.1063/1.1759085View Description Hide Description
Zirconiumtin titanium oxide doped 1 wt % ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 350 W with various argon-oxygen mixture and different substrate temperatures. Electrical properties and microstructures of ZnO-doped thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different ratios and substrate temperatures have been investigated. The surfacestructural and morphological characteristics analyzed by x-ray diffraction, scanning electron microscopy, and atomic force microscope were sensitive to the deposition conditions, such as ratio (100/0–80/20) and substrate temperature (350 °C–450 °C). The selected-area diffraction pattern showed that the depositedfilms exhibited a polycrystalline microstructure. All films exhibited ZST (111) orientation perpendicular to the substrate surface and the grain size as well as the deposition rate of the films increased with the increase of both the Ar partial pressure and the substrate temperature. At a ratio of 100/0, rf power level of 350 W and substrate temperature of 450 °C, the films with 6.44 μm thickness possess a dielectric constant of 42 (at 10 MHz), a dissipation factor of 0.065 (at 10 MHz), and a leakage current density of at an electrical field of 1 kV/cm.
96(2004); http://dx.doi.org/10.1063/1.1758314View Description Hide Description
We have carried out dielectric and Raman spectroscopy studies at the 298–623 K temperature range in polycrystallinethin filmsgrown by a soft chemical method. The diffuse phase-transition behavior of the thin films was observed by means of the dielectric constant versus temperature curves, which show a broad peak. Such behavior was confirmed later by Raman spectroscopy measurements up to 823 K, indicating that a diffuselike phase transition takes place at around 548–573 K. The damping factor of the soft mode was calculated using the damped simple harmonic oscillator model. On the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of a breakdown of the microscopic local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broad bands at some temperature interval above the ferroelectric-paraelectric phase-transition temperature suggested a diffuse nature of the phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in this thin film.