Volume 87, Issue 3, 01 February 2000
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
87(2000); http://dx.doi.org/10.1063/1.372031View Description Hide Description
Charged grain boundaries between crystalline blocks in bulk and thin film samples of incipient ferroelectrics are considered as charged defects producing a built-in electric field which is treated as a statistical dispersion of the biasing field. The normalized statistic dispersion of a biasing field, denoted as is used as one of the parameters of a phenomenological model of the dielectric response of incipient ferroelectrics. The surface charge density on the grain boundary is quantitatively estimated on the basis of a multiple-scattering analysis of spatially resolved electron-energy-loss spectra of the boundary between crystalline blocks in The built-in electric field in the incipient ferroelectrics is quantitatively estimated by the parameter which determines some specific features of the dielectric response of the incipient ferroelectric single crystal and thin film samples.
Suppression of bulk wave radiation from leaky surface acoustic waves by loading with thin dielectric films87(2000); http://dx.doi.org/10.1063/1.372032View Description Hide Description
The bulk wave, which is radiated into the substrate from the leaky surface acoustic wave (LSAW), can be suppressed by loading the substrate with a thin film of dielectric such as tantalum pentoxide and silicon dioxide Rotated Y-cut X-propagating lithium niobate is used for the substrate. For a certain range of the rotation angle, the attenuation of the LSAW can be suppressed by choosing the appropriate material and thickness for the film. For the free surface of 64° with film, and the metallized surface of 41° with film, the measured propagation losses decreased approximately to one-fourth to half of that of the sample without the thin film. It is shown that, even if the propagation path is a free surface, the particle displacement distribution in the LSAW is concentrated near the substrate surface by the loading with the thin film, as for the metallized surface. This result suggests that the bulk wave radiation in the LSAW excitation can be suppressed. The bulk wave radiation loss for the 41° with the film decreased approximately to one-sixth of that of the sample without the thin film.
Electrical characteristics of thin films deposited by reactive pulsed direct-current magnetron sputtering87(2000); http://dx.doi.org/10.1063/1.372033View Description Hide Description
Room temperature deposition of tantalum oxide films on metallized silicon substrates was investigated by reactive pulsed magnetron sputtering of Ta in an ambient. The dielectric constant of the tantalum oxide ranged from 19 to 31 depending on the oxygen percentage used during sputtering. The leakage current density was less than 10 nA/cm2 at 0.5 MV/cm electric field and the dielectric breakdown field was greater than 3.8 MV/cm for A charge storage as high as 3.3 μF/cm2 was achieved for 70-Å-thick film. Pulse frequency variation (from 20 to 200 kHz) did not give a significant effect in the electrical properties(dielectric constant or leakage current density) of the films.
87(2000); http://dx.doi.org/10.1063/1.372034View Description Hide Description
The internal friction (IF) and the Young’s modulus of (SBT) ceramics were measured by using the reed vibration method in the temperature range from 100 to 600 K with kilo-hertz frequencies. A high IF peak associated with a modulus defect appeared around 500 K, which was assumed to be due to the migration of oxygen vacancies with the activation energyU of about 0.95 eV. The mechanism of the IF peak was discussed in detail. At 570 K, an IF peak due to the viscous motion of domain walls near the Curie temperature was found. Below room temperature, a low IF peak with a modulus defect was found with peak temperature of 200–250 K, which varied for tens of degrees in different samples. This peak was due to the depinning process of 90° domain walls from oxygen vacancies. These results can be helpful in explaining the excellent fatigue resistance property of SBT thin films at room temperature.
87(2000); http://dx.doi.org/10.1063/1.372035View Description Hide Description
Field-induced phase transitions of antiferroelectric–ferroelectric nature have been investigated in the system. Samples of compositions located in the vicinity of an antiferroelectric–ferroelectric phase boundary, were analyzed by x-ray diffraction, by dielectric, and by electro-mechanical measurements. Samples with exhibited a metrically tetragonal structure, whereas the sample with exhibited a rhombohedral structure. From the electromechanical measurements, the compositions deepest in the antiferroelectric phase field were initially located in the antiferroelectric phase field The samples showed a pure electrostrictive behavior at low electric fields but underwent a phase transition into another antiferroelectric phase when submitted to higher electric fields. For intermediate compositions with the electric field enforced a transition between the antiferroelectric phase and the ferroelectric phase. In the latter compositional range, remanent ferroelectric behavior was detected at zero field and increased with Ti content until the ferroelectric phase remained metastable, in analogy with the better studied and systems.