Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Recent progress in relaxor ferroelectrics with perovskite structure

Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

Domains in ferroelectrics were considered to be well understood by the middle of the last century: They were generally rectilinear, and their walls were Ising-like. Their simplicity stood in stark contrast to the more complex Bloch walls or N\'eel walls in magnets. Only within the past decade and with the introduction of atomic-resolution studies via transmission electron microscopy, electron holography, and atomic force microscopy with polarization sensitivity has their real complexity been revealed. Additional phenomena appear in recent studies, especially of magnetoelectric materials, where functional properties inside domain walls are being directly measured. In this paper these studies are reviewed, focusing attention on ferroelectrics and multiferroics but making comparisons where possible with magnetic domains and domain walls. An important part of this review will concern device applications, with the spotlight on a new paradigm of ferroic devices where the domain walls, rather than the domains, are the active element. Here magnetic wall microelectronics is already in full swing, owing largely to the work of Cowburn and of Parkin and their colleagues. These devices exploit the high domain wall mobilities in magnets and their resulting high velocities, which can be supersonic, as shown by Kreines' and co-workers 30 years ago. By comparison, nanoelectronic devices employing ferroelectric domain walls often have slower domain wall speeds, but may exploit their smaller size as well as their different functional properties. These include domain wall conductivity (metallic or even superconducting in bulk insulating or semiconducting oxides) and the fact that domain walls can be ferromagnetic while the surrounding domains are not.

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Domain wall nanoelectronics

2.4.2. Interpenetrated Ladders 711 2.4.3. Unusual Motifs of Ladders 713 2.4.4. Properties of Ladderlike Chains 713 2.5. Rotaxane Polymers 714 2.5.1. 1D Polyrotaxanes 714 2.5.2. 2D Polyrotaxanes 715 2.5.3. 3D Polyrotaxanes 716 2.5.4. Hydrogen-Bonded Polyrotaxanes 716 2.6. Ribbon/Tape Polymers 717 2.7. Metal Cluster As Building Blocks for 1D CP 718 2.7.1. Metal Carboxylate Clusters 718 2.7.2. Metal Halide Clusters 719 2.7.3. Metal Chalcogenide Clusters 720 2.7.4. Polyoxometalate Clusters 721 2.7.5. Single Molecular Magnets as Building Blocks 722

One-Dimensional Coordination Polymers: Complexity and Diversity in Structures, Properties, and Applications

Perovskite lead-free dielectrics for energy storage applications

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.

https://www.worldscientific.com/doi/pdf/10.1142/S2010135X1241010X

Dielectric relaxation in relaxor ferroelectrics

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...

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

Dielectric permittivity \ensuremath{\varepsilon} as a function of temperature is measured in ${\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ and a number of other relaxor ferroelectrics with the perovskite structure. It is found that the data taken from the high-temperature slopes of the diffused permittivity peaks of all the materials studied can be collapsed onto a single scaling line derived from the formula ${\ensuremath{\varepsilon}}_{A}/\ensuremath{\varepsilon}=1+0.5(T\ensuremath{-}{T}_{A}{)}^{2}/{\ensuremath{\delta}}^{2},$ where ${\ensuremath{\varepsilon}}_{A},$ ${T}_{A},$ and \ensuremath{\delta} are the parameters depending on the composition. This formula describes the static conventional relaxor susceptibility, which provides the dominant contribution to the permittivity peak at temperatures above the temperature of the maximum. In the close vicinity of the peak temperature and below, the scaling is disturbed due to the conventional relaxor dispersion.

Empirical scaling of the dielectric permittivity peak in relaxor ferroelectrics

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.

Alexei A. Bokov

Papers

Recent progress in relaxor ferroelectrics with perovskite structure

Dielectric relaxation in relaxor ferroelectrics

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

Empirical scaling of the dielectric permittivity peak in relaxor ferroelectrics

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