74 research outputs found

    Effects of ac-field amplitude on the dielectric susceptibility of relaxors

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    The thermally activated flips of the local spontaneous polarization in relaxors were simulated to investigate the effects of the applied-ac-field amplitude on the dielectric susceptibility. It was observed that the susceptibility increases with increasing the amplitude at low temperatures. At high temperatures, the susceptibility experiences a plateau and then drops. The maximum in the temperature dependence of susceptibility shifts to lower temperatures when the amplitude increases. A similarity was found between the effects of the amplitude and frequency on the susceptibility.Comment: 8 pages, 7 figures, Phys. Rev. B (in July 1st

    Dielectric nonlinearity of relaxor ferroelectric ceramics at low ac drives

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    Dielectric nonlinear response of (PbMg1/3_{1/3}Nb2/3_{2/3}O3_3)0.9_{0.9}(PbTiO3_3)0.1_{0.1} (0.9PMN-0.1PT) relaxor ceramics was investigated under different ac drive voltages. It was observed that: (i) the dielectric permittivity is independent on ac field amplitude at high temperatures; (ii) with increasing ac drive, the permittivity maximum increases, and the temperature of the maximum shifts to lower temperature; (iii) the nonlinear effect is weakened when the measurement frequency increases. The influences of increasing ac drive were found to be similar to that of decreasing frequency. It is believed that the dielectric nonlinearities of relaxors at low drives can be explained by the phase transition theory of ergodic space shrinking in succession. A Monte Carlo simulation was performed on the flips of micro polarizations at low ac drives to verify the theory.Comment: Submitted to J. Phys.: Cond. Matte

    Coexistence of the Critical Slowing Down and Glassy Freezing in Relaxor Ferroelectrics

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    We have developed a dynamical model for the dielectric response in relaxor ferroelectrics which explicitly takes into account the coexistence of the critical slowing down and glassy freezing. The application of the model to the experiment in PMN allowed for the reconstruction of the nonequilibrium spin glass state order parameter and its comparison with the results of recent NMR experiment (Blinc et al., Phys. Rev. Lett. 83, No. 2 (1999)). It is shown that the degree of the local freezing is rather small even at temperatures where the field-cooled permittivity exceeds the frequency dependent permittivity by an order of magnitude. This observation indicates the significant role of the critical slowing down (accompanying the glass freezing) in the system dynamics. Also the theory predicts an important interrelationship between the frequency dependent permittivity and the zero-field-cooled permittivity, which proved to be consistent with the experiment in PMN (A. Levstik et. al., Phys. Rev. B 57, 11204 (1998))

    Dynamics of relaxor ferroelectrics

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    We study a dynamic model of relaxor ferroelectrics based on the spherical random-bond---random-field model and the Langevin equations of motion. The solution to these equations is obtained in the long-time limit where the system reaches an equilibrium state in the presence of random local electric fields. The complex dynamic linear and third-order nonlinear susceptibilities χ1(ω)\chi_1(\omega) and χ3(ω)\chi_3(\omega), respectively, are calculated as functions of frequency and temperature. In analogy with the static case, the dynamic model predicts a narrow frequency dependent peak in χ3(T,ω)\chi_3(T,\omega), which mimics a transition into a glass-like state.Comment: 15 pages, Revtex plus 5 eps figure

    Lead-free piezoceramics - Where to move on?

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    Lead-free piezoceramics aiming at replacing the market-dominant lead-based ones have been extensively searched for more than a decade worldwide. Some noteworthy outcomes such as the advent of commercial products for certain applications have been reported, but the goal, i.e., the invention of a lead-free piezocermic, the performance of which is equivalent or even superior to that of PZT-based piezoceramics, does not seem to be fulfilled yet. Nevertheless, the academic effort already seems to be culminated, waiting for a guideline to a future research direction. We believe that a driving force for a restoration of this research field needs to be found elsewhere, for example, intimate collaborations with related industries. For this to be effectively realized, it would be helpful for academic side to understand the interests and demands of the industry side as well as to provide the industry with new scientific insights that would eventually lead to new applications. Therefore, this review covers some of the issues that are to be studied further and deeper, so-to-speak, lessons from the history of piezoceramics, and some technical issues that could be useful in better understanding the industry demands. As well, the efforts made in the industry side will be briefly introduced for the academic people to catch up with the recent trends and to be guided for setting up their future research direction effectively.ope

    X-Ray Microbeam Evaluation of Domain Switching near Fatigue Cracks in Piezoelectric Ceramics (PZT)

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    Piezoelectric d 15

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    Crossover in a non-analytical behaviour of dielectric non-linearity in PbMg1/3Nb2/3O3 relaxor ferroelectric

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    The dielectric response of the relaxer ferroelectric PbMg1/3Nb2/3O3 (PMN) is found to be a non-analytical function of the ac field, with the absolute value of the non-linear component of the polarization given by \P-nl\ alpha E-m(gamma(omega,T)). The dependence on the temperature, T, and frequency, omega, of the exponent gamma manifests itself in the form of a crossover in gamma(T) from approximately 2 to 3 upon cooling, whose position depends upon the frequency of the applied ac held. From the comparison of y(w, T) with the linear complex dielectric permittivity, epsilon(l)* (omega, T), of PMN, the following can be correlated: (i) gamma approximate to 2 in the regime of the quasi-static response, and y starts deviating from 2 simultaneously with the onset of the frequency dispersion; and (ii) gamma approximate to 3 when the spectrum of relaxation times in PMN becomes flat. These findings can be understood in terms of the change in the type of the motion of the interphase boundaries of the microscopic polar regions existing in PMN, namely in the change of the scale on which the interphase boundaries can move
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