46 research outputs found
Effects of ac-field amplitude on the dielectric susceptibility of relaxors
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
Dielectric nonlinear response of
(PbMgNbO)(PbTiO) (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
Dynamics of relaxor ferroelectrics
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
and , 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 ,
which mimics a transition into a glass-like state.Comment: 15 pages, Revtex plus 5 eps figure
Coexistence of the Critical Slowing Down and Glassy Freezing in Relaxor Ferroelectrics
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))
X-Ray Microbeam Evaluation of Domain Switching near Fatigue Cracks in Piezoelectric Ceramics (PZT)
Crossover in a non-analytical behaviour of dielectric non-linearity in PbMg1/3Nb2/3O3 relaxor ferroelectric
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
Mechanism of polarization response in the ergodic phase of a relaxor ferroelectric
It is shown that the effects of large de bias and ac driving fields on the dielectric permittivity of single crystals of PbMg1/3Nb2/3O3 (PMN) relaxer ferroelectric exhibit very different behavior, including anisotropy and sign of the effect, which is traced up to the high-temperature interval in the ergodic phase. The observed phenomena strongly suggest that in the ergodic phase of PMN the dielectric response to the ac field is controlled by a side-way motion of the interphase boundaries of the polar regions, rather than by the thermally activated reorientations of the local spontaneous polarization
Does freezing in PbMg1/3Nb2/3O3 relaxor manifest itself in nonlinear dielectric susceptibility?
A possible anomaly in the temperature dependence of nonlinear dielectric susceptibility chi(nl) of relaxor ferroelectrics related with the freezing phase transition was investigated. First, based on the phenomenological approach, the anomaly in the chi(nl) was analyzed, including its shape, sign, and crystalline anisotropy. Second, the theoretical results were applied to the analysis of experimental data on nonlinear dielectric permittivity of single crystals of PbMg1/3Nb2/3O3 (PMN) relaxor. It was concluded that in contrast to earlier publications, there is no evidence for the anomaly in chi(nl)(T) of PMN related with the freezing transition. (C) 1999 American Institute of Physics
A "breathing" model for the polarization response of relaxer ferroelectrics
The present paper proposes a model of relaxer ferroelectrics, which describes the polarization response of these materials in terms of vibration of the interphase boundary between the polar regions and nonpolar matrix. The model is formulated and is applied to explain various features of the polarization response of a "classical" relaxer, PbMg1/3Nb2/3O3, such as the relaxation dispersion of the linear response, its temperature dependence, and the nonlinear effects due to large ac and/or de fields
Dielectric non-linearity and the nature of polarization response of PbMg1/3Nb2/3O3 relaxor ferroelectric
We investigate the non-linear dielectric properties of PbMg1/3Nb2/3O3 (PMN) single crystals and present the following experimental evidence: (a) the absence of the anomaly in the temperature dependence of non-linear coefficients in the relationship between the electric field and polarization, E(P); (b) large difference between the "ac" and "dc" non-linear effects; (c) non-analytical behavior of non-linear dielectric response and the crossover in its field exponents. The fact (a) clearly evidences against the glassy behavior of PMN. The results (b) and (c) can be understood using the model of the interphase boundary motion in PMN