Volume 89, Issue 3, 01 February 2001
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
89(2001); http://dx.doi.org/10.1063/1.1335650View Description Hide Description
The electromechanical performance characteristics of ceramics and 〈001〉-oriented crystals have been investigated under uniaxial stress (σ). The results demonstrate that 〈001〉-oriented crystals have an electromechanical coupling coefficient of ∼0.9 for σ less than The results also demonstrate that the acoustical energy density of ceramics and 〈001〉-oriented crystals are not significantly different at field levels below 15 kV/cm.
Investigations of electrostrictive ceramics under high-power drive conditions: Importance of compositional fluctuations on residual hysteresis89(2001); http://dx.doi.org/10.1063/1.1335651View Description Hide Description
The high-field polarization behavior of electrostrictive ceramics has been investigated as a function of measurement frequency, drive field, and temperature. It was observed that hysteretic losses increase with increasing frequency. Significant variations in loss were found between specimens of similar composition obtained from different sources, which became more pronounced with increasing temperature. The results indicate that careful synthesis and processing are crucial to the thermal stability of electrostrictive ceramics in high-power source applications. Further investigations revealed the potential use of accelerated aging by substituent introduction for mitigation of thermal stability concerns.
89(2001); http://dx.doi.org/10.1063/1.1334938View Description Hide Description
The nanoscale mechanism of retention behavior in (SBT) thin films has been investigated by means of piezoresponse scanning force microscopy. It has been found that SBT films with Pt electrodes (SBT/Pt) exhibit a strong dependence of retention characteristics upon domain polarity: positive domains with the polarization vector pointing to the bottom electrode exhibit excellent stability in sharp contrast to the negative domains which show poor retention. The backswitching of the negative domains proceeds via sidewise motion of the domain walls and shows a log-time dependence. The strong effect of the poling voltage parameters (duration and amplitude) and the previous switching pattern on domain retention behavior is reported. On the other hand, in SBT films with electrodes the written domains of both polarities show no sign of relaxation to the original state irrespective of the parameters of the poling voltage. The difference in retention behavior of opposite domains in SBT/Pt films is explained by the presence of the polarization-independent built-in bias at the SBT/Pt interface pointing to the bottom electrode. This built-in bias triggers the backswitching of a negative domain by generating positive nuclei at the interface. The forward growth of the nuclei is further governed by the field of the space charge which screens the original polarization state. The symmetric retention behavior and the stability of domain in SBT films with electrodes are attributed to the inhibition of the nucleation process at the interface.
89(2001); http://dx.doi.org/10.1063/1.1334937View Description Hide Description
A method for investigating the nature of thermally activated relaxations in terms of their cooperative character is tested in both polymer and low molecular weight crystal systems. This approach is based on analysis of the activation entropy in order to describe thermally activated relaxations. The betaine arsenate/phosphate mixed system of low molecular weight crystals was selected for investigation because pure compounds of this system show ferro-/antiferroelectric phase transitions and the mixed crystals undergo different kinds of relaxation processes involving both dipole–dipole and dipole–lattice interactions. The polymer chosen was a side chain liquid-crystalline polysiloxane, which shows the β-relaxation characteristic of disordered systems and amorphous materials. The cooperative versus local character of the relaxations is described in terms of “complex” and “simple” relaxations based on calculations of the activation entropies. The initial assumptions of the theory, as well as the resulting equations, were found to be applicable to the systems studied.
89(2001); http://dx.doi.org/10.1063/1.1336518View Description Hide Description
Dielectric spectroscopy and dc conductivity have been studied in and isomorphic crystals in a temperature range 150–400 K. The experimental data indicate two temperature regions related to different types of relaxation processes. Alternation of the activation energy, suppression of the dielectricdispersion, and decreasing dissipation factor by three orders of magnitude has shown that the superionic state in and its isomorphs transit gradually to the dielectric state with temperature lowering. The transition leads to variation of transport properties from ionic to electronic conductivity. It was found that the parameters of the relaxation process (activation energy in the superionic state, temperature range of transition from ionic to electron conductivity) are determined by the sort of mobile cations. The temperature dependence of conductivityrelaxation time was obtained from the electric modulus plots.