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

A wide variety of experimental results and theoretical investigations in recent years have convincingly demonstrated that several transition metal oxides and other materials have dominant states that are not spatially homogeneous. This occurs in cases in which several physical interactions-spin, charge, lattice, and/or orbital-are simultaneously active. This phenomenon causes interesting effects, such as colossal magnetoresistance, and it also appears crucial to understand the high-temperature superconductors. The spontaneous emergence of electronic nanometer-scale structures in transition metal oxides, and the existence of many competing states, are properties often associated with complex matter where nonlinearities dominate, such as soft materials and biological systems. This electronic complexity could have potential consequences for applications of correlated electronic materials, because not only charge (semiconducting electronic), or charge and spin (spintronics) are of relevance, but in addition the lattice and orbital degrees of freedom are active, leading to giant responses to small perturbations. Moreover, several metallic and insulating phases compete, increasing the potential for novel behavior.

http://science.sciencemag.org/content/sci/309/5732/257.full.pdf

Complexity in Strongly Correlated Electronic Systems

Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

After twenty years of partly quiet and ten years of partly enthusiastic research into lead-free piezoceramics there are now clear prospects for transfer into applications in some areas. This mimics prior research into eliminating lead from other technologies that resulted in restricted lead use in batteries and dwindling use in other applications. A figure of merit analysis for key devices is presented and used to contrast lead-containing and lead-free piezoceramics. A number of existing applications emerge, where the usage of lead-free piezoceramics may be envisaged in the near future. A sufficient transition period to ensure reliability, however, is required. The use of lead-free piezoceramics for demanding applications with high reliability, displacements and frequency as well as a wide temperature range appears to remain in the distant future. New devices are outlined, where the figure of merit suggests skipping lead-containing piezoceramics altogether. Suggestions for the next pertinent research requirements are provided.

Transferring lead-free piezoelectric ceramics into application

The perovskites and perovskite-related structures exhibit several features of technical as well as fundamental interest. Technically useful properties include oxide-ion conduction with/without electronic conduction, oxidation catalysis, ferroic displacements in classic and relaxor ferroelectrics, half-metallic ferromagnetism and high-temperature superconductivity. Of more fundamental interest is the ability to tune, by chemical substitution on the large-cation subarray, transition-metal oxides through the crossover on the transition-metal array from localized dn configurations to itinerant d-electron behaviour without/with changing the valence state of that array. The localized-electron configurations may exhibit cooperative Jahn–Teller distortions that introduce anisotropic exchange interactions. At crossover, bond-length fluctuations may segregate into an ordered array of alternating covalent and ionic bonding in a single-valent perovskite; multicentre polarons or correlation bags may replace small polarons in a mixed-valent system. Bond-length fluctuations at crossover give vibronic conduction and suppression of the phonon contribution to the thermal conductivity; the fluctuations may order, to give high-temperature superconductivity, or transform to quantum–critical-point behaviour at lowest temperatures. Crossover of σ-bonding electrons in the presence of localized spins associated with π-bonding electrons gives rise to the colossal magnetoresistance phenomenon above a ferromagnetic Curie temperature.

https://iopscience.iop.org/article/10.1088/0034-4885/67/11/R01/pdf

Electronic and ionic transport properties and other physical aspects of perovskites

The temperature dependence of the Edwards-Anderson order parameter ${q}_{\mathrm{EA}}$ and the local polarization distribution function $W(\stackrel{\ensuremath{\rightarrow}}{p})$ have been determined in a PMN single crystal via 2D ${}^{93}\mathrm{Nb}$ NMR. A glasslike freezing of reorientable polar clusters occurs in the temperature range of the diffuse relaxor transition, whereas the NMR spectra corresponding to pinned nanodomains do not change with temperature. The obtained form of $W(\stackrel{\ensuremath{\rightarrow}}{p})$ as well as the temperature dependence of ${q}_{\mathrm{EA}}$ and the nonlinear dielectric susceptibility can be well described by a newly proposed spherical random bond--random field model of relaxor ferroelectrics.

/pdf/local-polarization-distribution-and-edwards-anderson-order-3puqkbozfr.pdf

Local Polarization Distribution and Edwards-Anderson Order Parameter of Relaxor Ferroelectrics

The local structure of the relaxor single crystal PMN has been studied via a measurement of the temperature dependences of the ${}^{207}\mathrm{Pb}$ spectra and relaxation times between 450 K and 15 K. The ${}^{207}\mathrm{Pb}$ NMR spectra are frequency distributions which reflect the existence of polar nanoclusters and which can be well described by the recently proposed spherical random-bond--random-field model. The temperature dependence of the Edwards-Anderson order parameter q has been determined together with the random bond coupling and the random field variance. The results agree with those obtained from the ${}^{93}\mathrm{Nb}$ NMR spectra and show that at any given instant of time the crystal consists of polar clusters with variable orientation and magnitude of the local polarization. The polar clusters are on the NMR time scale ${10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}5} \mathrm{s},$ dynamic entities which exist for a certain amount of time, disappear, and then reappear in a different form.

207 Pb NMR study of the relaxor behavior in PbMg 1/3 Nb 2/3 O 3

The ${}^{93}\mathrm{Nb}$ and ${}^{45}\mathrm{Sc}$ nuclear-magnetic-resonance (NMR) spectra of disordered relaxor ferroelectrics ${\mathrm{PbSc}}_{1/2}{\mathrm{Nb}}_{1/2}{\mathrm{O}}_{3}$ (PSN) and ${\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ (PMN) have been studied at $Tg{T}_{m},$ where ${T}_{m}\ensuremath{\approx}355\mathrm{K}$ and 265 K is the temperature of the dielectric susceptibility maximum for PSN and PMN, respectively. The analysis of the spectra was performed both on the basis of an analytical description of the NMR line shapes, allowing for homogeneous and inhomogeneous broadening related to a random distribution of the electric-field gradients, and a numerical Monte Carlo approach taking into account electric-field gradients originating from the random distribution of Mg, Sc, and Nb ions (which may be shifted or not) over B-type cation sites. $1/2\ensuremath{\leftrightarrow}\ensuremath{-}1/2$ NMR spectra of ${}^{93}\mathrm{Nb}$ and ${}^{45}\mathrm{Sc}$ in PSN contain a narrow (3--4 kHz) almost isotropic component and a broad strongly anisotropic component. These two components of the NMR spectra are related to the 1:1 Sc/Nb ordered and compositionally disordered regions of the crystal, respectively. It is shown that in the disordered regions, the ${\mathrm{Sc}}^{3+},$ ${\mathrm{Nb}}^{5+},$ and ${\mathrm{O}}^{2\ensuremath{-}}$ ions are randomly shifted from their cubic lattice sites in one of the three possible directions: $〈100〉,$ $〈110〉,$ or $〈111〉.$ In PMN, the NMR spectrum of ${}^{93}\mathrm{Nb}$ contains practically only the broad component. The portion of the unbroadened spectrum that may correspond to ideal 1:2 Mg/Nb ordered regions accounts only for 2--3 % of the total integral intensity. No evidence was obtained for the existence of 1:1 Mg/Nb regions in PMN. The NMR data demonstrate that in PMN the cubic symmetry at $Tg{T}_{m}$ is locally broken due to ion shifts similar to that in disordered PSN. The values of the ionic shifts have been estimated in the point-charge point-dipole approximation for the electric-field gradients both in PSN and PMN.

NMR study of local structure and chemical ordering in PbMg 1 / 3 Nb 2 / 3 O 3 and PbSc 1 / 2 Nb 1 / 2 O 3 relaxor ferroelectrics

TNT detection with 14N NQR: multipulse sequences and matched filter.

In this work, we investigate off-resonance effect on the (14)N nuclear quadrupole resonance magnetization decay during the spin-lock spin-echo pulse sequence (SLSE). The compound chosen for this study is paranitrotoluene with a single (14)N site, which represents a suitable simplified model for the explosive trinitrotoluene with six nonequivalent (14)N sites. We find that the quasi-steady state magnetization exhibits dips at particular frequency offsets and more interestingly that its decay rate T(2 eff) (-1) exhibits similar dips (slower decay) at the same frequency offsets. The coexistence of dips is very important for applications where the primary use of the SLSE sequence is to increase the signal-to-noise ratio, as longer sampling times compensate for small magnetization values. A theory explaining both observations is presented which includes homonuclear dipolar interactions and spin coupling to the lattice. We show that the homonuclear dipolar interaction contributes only 20% to the total magnetization decay rate, while spin-lattice coupling is the dominant mechanism.

A. Gregorovič

Papers

Local Polarization Distribution and Edwards-Anderson Order Parameter of Relaxor Ferroelectrics

207 Pb NMR study of the relaxor behavior in PbMg 1/3 Nb 2/3 O 3

NMR study of local structure and chemical ordering in PbMg 1 / 3 Nb 2 / 3 O 3 and PbSc 1 / 2 Nb 1 / 2 O 3 relaxor ferroelectrics

TNT detection with 14N NQR: multipulse sequences and matched filter.

Relaxation during spin-lock spin-echo pulse sequence in (14)N nuclear quadrupole resonance.