Alexei A. Bokov

Ferroelectric to relaxor crossover and dielectric phase diagram in the BaTiO3-BaSnO3 system

The (1−x)BaTiO3–xBaSnO3 (0⩽x⩽0.30) perovskite solid solution ceramics were prepared by solid state reaction and studied by dielectric spectroscopy. The complex dielectric permittivity was measured as a function of frequency (0.1Hz–100kHz) in the temperature (T) range of 123–573K. The transition from the high-temperature paraelectric state where the dielectric constant obeys the Curie-Weiss law to the ergodic cluster state is found to occur at the same temperature of 485K in all the compositions of x⩾0.04 and at lower temperatures in those with a smaller x. For 0⩽x⩽xc=0.19, the temperature of the dielectric peak Tm, corresponding to the diffuse transition from the ergodic polar cluster state to the ferroelectric state, decreases with increasing x and does not depend on frequency. The diffuseness of the peak gradually increases. For x>xc, the permittivity exhibits relaxor behavior with the frequency-dependent Tm satisfying the Vogel-Fulcher law. The temperature variation of the permittivity on the high-temp...

DIELECTRIC RELAXATION IN RELAXOR FERROELECTRICS

In this review the dielectric properties of relaxor ferroelectrics are discussed and compared with the properties of normal dielectrics and ferroelectrics. We try to draw a general picture of dielectric relaxation starting from a textbook review of the underlying concepts and pay attention to common behavior of relaxors rather than to the features observed in specific materials. We hope that this general approach is beneficial to those physicists, chemists, material scientists and device engineers who deal with relaxors. Based on the analysis of dielectric properties, a comprehensive definition of relaxors is proposed: relaxors are defined as ferroelectrics in which the maximum in the temperature dependence of static susceptibility occurs within the temperature range of dielectric relaxation, but does not coincide with the temperature of singularity of relaxation time or soft mode frequency.

Phenomenological description of dielectric permittivity peak in relaxor ferroelectrics

Abstract We found that, at the so-called diffuse phase transition in relaxor ferroelectrics, the dielectric permittivity e obeys the relation e A / e =1+0.5( T − T A ) 2 / δ A 2 in a wide temperature range above the temperature of permittivity maximum T m ( T m > T A ). The parameter δ A remains invariant with the variation of measurement frequency and characterizes the diffuseness of the transition.

Development of ferroelectric order in relaxor (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (0≤x≤0.15)

The microstructure and phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain to be some of the most puzzling issues of solid-state science. In the present work we have investigated the evolution of the phase symmetry in PMN-xPT ceramics as a function of temperature (20<T<500 K) and composition (0≤x≤0.15) by means of high-resolution synchrotron x-ray diffraction. Structural analysis based on the experimental data reveals that the substitution of Ti4+ for the complex B-site (Mg1/3Nb2/3)4+ ions results in the development of a clean rhombohedral phase at a PT concentration as low as 5%. The results provide insight into the development of ferroelectric order in PMN-PT, which has been discussed in light of the kinetics of polar nanoregions and the physical models of the relaxor ferroelectrics to illustrate the structural evolution from a relaxor to a ferroelectric state.

Domain structure in the monoclinic Pm phase of Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

The domain structure of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystals with composition x≈0.33 in the range of the morphotropic phase boundary (MPB) was studied. Based on the analysis of spontaneous strain compatibility and charge of domain walls, we have established the permissible domain arrangements for the ferroelectric phases of different symmetries, which are expected to occur in the range of the MPB. Examination of (001)-oriented unpoled and electrically poled (along the [001] direction) crystal plates in a polarizing microscope reveals a monophase state with the domain structure compatible with the structure theoretically predicted for the MC monoclinic phase (space group Pm), which was recently discovered in the compositions close to the MPB by x-ray and neutron diffraction studies. In the unpoled crystal, the 180° walls between the domains whose spontaneous polarization vectors are parallel to the plane of the crystal plate (i.e., a-domains) are observed. The domain structure of the poled crystal...

Dielectric dispersion and critical behavior in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3

A critical behavior of dielectric susceptibility has been discovered in relaxor ferroelectric 0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3. The real part of permittivity e′ was found to follow the relation e′−e∞=χ′∝(T−T0)−2 at T>T0, and e′∝(TC−T)−1 at T<TC, where T0≈TC<Tm; Tm is the temperature of the diffused e′(T) maximum as is typical of relaxors; e∞ is the frequency-independent parameter, and χ′ is the susceptibility depending on frequency via the “universal” relaxation law χ′∝fn−1. The susceptibility χ′ is suggested to originate from the polarization of polar nanoclusters.

Recent advances in diffuse ferroelectric phase transitions

Abstract Models for understanding the properties of relaxor ferroelectrics are reviewed, a new model being proposed.

Optically isotropic and monoclinic ferroelectric phases in Pb ( Zr 1 − x Ti x ) O 3 (PZT) single crystals near morphotropic phase boundary

We report the finding of unusual scale-dependent symmetry below the ferroelectric Curie temperature in the perovskite

Double freezing of dielectric response in relaxor Pb(Mg1/3Nb2/3)O3 crystals

\text{Pb}({\text{Zr}}_{1\ensuremath{-}x}{\text{Ti}}_{x}){\text{O}}_{3}

Role of random electric fields in relaxors

single crystals of morphotropic phase boundary compositions. The crystals of tetragonal symmetry on submicrometer scale exhibit a macroscopic (optically determined) cubic symmetry. This peculiar optical isotropy is explained by the anomalously small size of tetragonal ferroelectric domains. Upon further cooling the crystals transform to the phase consisting of micrometer-sized domains of monoclinic symmetry.