Volume 86, Issue 9, 01 November 1999
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
86(1999); http://dx.doi.org/10.1063/1.371497View Description Hide Description
Highly oriented perovskite films of and with compositions near the morphotropic phase boundary were formed by pulsed laser deposition on (100). The dielectric properties of the films were studied over the frequency range of 100 Hz–1 MHz in the temperature range The room temperature polarization and dielectric permittivity of 250-nm-thick films were close to those in bulk ceramics. The films exhibited relaxor-type behavior with thermal hysteresis and with the temperatures of the dielectric peaks corresponding to those in the bulk. The width of the transition in the films was larger than in bulk ceramics. The properties of the films were found to be influenced by the small grain size rather than by the interfaces of the films.
Study on the piezoresistive effect of crystalline and polycrystalline diamond under uniaxial strains86(1999); http://dx.doi.org/10.1063/1.371498View Description Hide Description
The piezoresistive effect of p-type crystalline materials under uniaxial stress was analyzed by the deformation-potential theory and the valence-bands split-off model. The calculation formula of the gauge factor under the condition of the strain-induced separation of the heavy- and light-hole bands was obtained. It is found that the great difference of the effective mass between the heavy and light hole in diamond is one of the main factors which are responsible for the piezoresistive effect in the p-type diamond. The piezoresistive effect of the p-type polycrystallinematerial was also discussed from the Mayadas–Shatzkes model. The results showed that the piezoresistive effect of polycrystallinematerials is related to both the valence-bands split off and the grain-boundary scattering. The grain-boundary scattering played a role of decreasing the piezoresistive effect, which made the polycrystallinematerials have a smaller gauge factor than the crystalline materials.
86(1999); http://dx.doi.org/10.1063/1.371499View Description Hide Description
Nanocrystalline (PCLT) powders were prepared by the sol–gel technique. Doping-induced or grain size-induced structure phase transition was investigated by using Raman scattering and x-ray diffraction for the PCLT system. Experimental results show that the soft phonon mode displays a decrease in frequency but an increase in linewidth with increasing concentration of La. A discontinuous behavior of the phonon energy is associated with a phase transition from a ferroelectric tetragonal to a paraelectric cubic phase, and occurs at a morphotropic phase boundary of for grain sizes being 20 nm. The dependence of Raman phonon modes on the size of particles has been analyzed for nanocrystalline with grain sizes of 10–60 nm and a grain size-induced phase transition is observed for sizes below 14 nm.
Frequency response and scaling of hysteresis for ferroelectric thin films deposited by laser ablation86(1999); http://dx.doi.org/10.1063/1.371500View Description Hide Description
The ferroelectrichysteresis response against periodically varying electric field over frequency range of Hz and amplitude range of 2–45 kV/cm for (YBCO)/ (PZT)/YBCO thin filmcapacitors prepared by laser ablation is measured by utilizing the Sawyer–Tower circuit. Given amplitude Δ of the field, the hysteresis area first grows and then decays as a function of frequency φ. At low and high ranges of frequency, can be scaled as and respectively. It is established that the dynamic hysteresis at the high frequency range for a PZTthin filmcapacitor does not follow the theoretically predicted scaling law. An empirical scaling law with the critical field and b a constant, is proposed to characterize the frequency and amplitude dependence of the hysteresis area over all the frequency range. In addition, the remnant polarization and coercive field as functions of φ are investigated, respectively, revealing a single-peaked pattern of both and