We propose a simple and solvable mean-field model of the scattering of transverse optic modes by Polarized Nano Regions (PNR) in the paraelectric phase of relaxor ferroelectrics. The PNR is assumed to be a ferroelectric sphere embedded in the host isotropic medium. The Lagrangian parameters are taken to be the same inside and outside the PNR, with exception of the soft-mode gap temperature dependence. The interaction of the Transverse (TO) with the longitudinal (LO) optic modes is taken into account but the latter is found to be important only at the surface of the PNR. Elementary excitations of the system are found to be of two types - Vortex (V) and Quasi Polar (QP). V excitations correspond to closed polarization lines or closed TO displacements while QP excitations contain open TO polarization lines, with an electric dipole if the net angular momentum j=1. LO waves are virtually excited only in the thin layer near the PNR surface and can be excluded from the boundary conditions without any consequence. The final boundary conditions include only V and QP TO wave amplitudes. Dynamical equations are solved and a phase diagram is predicted. The phase transition temperature is found to be lower for Vortex than for QP excitations. Therefore, the QP condensation (local phase transition) occurs before the Vortex one upon cooling. TO scattering by the PNR reveals strong long-wave resonances that can be shown to result from shallow localized and quasi-localized states and may be essential to understanding the waterfall observed in TO studies by inelastic neutron scattering.
Relaxor ferroelectrics are applied in electronic devices such as actuators and sonars. Morphotrophic phase boundaries (MPBs) with monoclinic structures are known for their high piezoelectricity and electromechanical coupling factors in solid solutions of PbTiO$_{3}$ and relaxor ferroelectrics (Pb(Mg$_{1/3}$, Nb$_{2/3}$)O$_{3}$ or Pb(Zn$_{1/3}$, Nb$_{1/3}$)O$_{3}$). However, the monoclinic structures related to polar nanosize domains (polar nanoregions) exhibiting the relaxor properties of dielectric dispersion have not been reported. Using transmission electron microscopy and synchrotron x-ray…
The existence of polar nanoregions is the most important characteristic of ferroelectric relaxors, however, the size determination and dynamic of PNRs remains uncertain. We reveal a re-entrant relaxor behavior and ferroelectric-paraelectric transition coexists in complex perovskite oxide 0.6Bi(Mg1/2Ti1/2)O3-0.4PbTiO3. Two dielectric anomalies (i) the low-temperature re-entrant relaxor transition and (ii) the high-temperature diffuse phase transition (DPT) were described by the phenomenological statistical model. The sizes of the two kinds of polar nanoregions (PNRs) corresponding to two ferroe…
Local inhomogeneities known as polar nanoregions (PNR) play a key role in governing the dielectric properties of relaxor ferroelectrics - a special class of material that exhibits an enormous electromechanical response and is easily polarized with an external field. Using neutron inelastic scattering methods, we show that the PNR can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT). A strong interaction is found between the PNR and the propagation of sound waves, i.e. acoustic phonons, the visibility of which can be enhan…
We present a quantitative analysis of the phonon lineshapes obtained by neutron inelastic scattering methods in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN). Differences in the shapes and apparent positions of the transverse acoustic (TA) and transverse optic (TO) phonon peaks measured in the (300) and (200) Brillouin zones at 690 K are well described by a simple model that couples the TA and soft TO modes in which the primary parameter is the wave vector and temperature-dependent TO linewidth Gamma(q,T). This mode-coupling picture provides a natural explanation for the uniform displacemen…
It is now well established that the unique properties of relaxor ferroelectrics are due to the presence of polar nanoregions (PNR's). We present recent results from Neutron and Raman scattering of single crystals of PZN, PZN-xPT, and PMN. Both sets of measurements provide information on the condensation of the PNR's and on their slow dynamics, directly through the central peak and, indirectly, through their coupling to transverse phonons. A comparative analysis of these results allows identification of three stages in the evolution of the PNR's with decreasing temperature: a purely dynamic sta…
A new class of superparamagnetism was found in relaxor ferroelectric 2/3BiFeO$_{3}$-1/3BaTiO$_{3}$. The size of the magnetic particle, estimated from the superparamagnetic magnetization curve, coincides with the size of the polar nanoregion (PNR), which governs the relaxor ferroelectric property. This suggests that the magnetic domain is identical to the PNR. The temperature variations in the sizes of the magnetic domains and PNRs estimated by our neutron diffraction measurements support this picture. Since the same domain provides both electric and magnetic properties, strong coupling between…
We have studied the neutron diffuse scattering in the relaxor PMN. The diffuse scattering appears around the Burns temperature (~620K), indicating its origin from the polar nanoregions (PNR). While the relative diffuse intensities are consistent with previous reports, they are entirely different from those of the lowest-energy TO phonon. Because of that, it has been considered that this TO mode could not be the ferroelectric soft mode. Recently, a neutron scattering study has unambiguously shown that the TO mode does soften on cooling. If the diffuse scattering in PMN originates from the soft …
Direct Imaging of Temperature Evolution of Polar Nanoregions and Chemically Ordered Regions in PMN Relaxor: Evidence for Polar Phase Percolation
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University（东北大学前沿跨学科研究院）；Institute of Multidisciplinary Research for Advanced Materials, Tohoku University（东北大学先进材料多学科研究中心）；Shizuoka University（静冈大学）；Institute of Science Tokyo（东京科学大学）
The dielectric permittivity e at frequencies from [10^(-1) -10^(-5)] Hz to 10^5 Hz is studied in perovskite (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 relaxor ferroelectric ceramics of different compositions x = 0.35, 0.25 and 0, which exhibit, below the temperature of the diffuse epsilon'(T) maximum Tm, a tetragonal ferroelectric, a rhombohedral ferroelectric and a nonergodic relaxor phase, respectively. The universal relaxor dispersion previously observed at temperatures near and above Tm in the ceramics of x=0.25, is also found to exist in other compositions. This dispersion is described by the fracti…
It has been considered that polar nanoregions in relaxors form at Burns temperature Td approx 600 K. High-temperature dielectric investigations of Pb(Mg1/3Nb2/3)O3 (PMN) and 0.7PMN-0.3PbTiO3 reveal, however, that the dielectric dispersion around 600 K appears due to the surface-layer contributions. The intrinsic response, analyzed in terms of the universal scaling, imply much higher Td or formation of polar nanoregions in a broad temperature range, while high dielectric constants manifest that polar order exists already at the highest measured temperatures of 800 K. The obtained critical expon…
We use neutron scattering to characterize the acoustic phonons in the relaxor PMN and demonstrate the presence of an anisotropic damping mechanism directly related to short-range, polar correlations. For a large range of temperatures above Tc ~ 210, K, where dynamic polar correlations exist, acoustic phonons propagating along [1\bar{1}0] and polarized along [110] (TA2 phonons) are overdamped and softened across most of the Brillouin zone. By contrast, acoustic phonons propagating along [100] and polarized along [001] (TA1 phonons) are overdamped and softened for only a limited range of wavevec…
Relaxor ferroelectrics have been a focus of intense attention due to their anomalous dielectric characteristics, diffuse phase transitions, and strong piezoelectricity. Understanding the structure and dynamics of relaxors has been one of the long-standing challenges in solid-state physics, with the current model of polar nanoregions in a non-polar matrix providing only a qualitative description of the relaxor phase transitions. In this paper, we investigate the local structure and dynamics in 75%PbMg$_{1/3}$Nb$_{2/3}$O$_3$-25%PbTiO$_3$ (PMN-PT) using molecular dynamics simulations and the dyna…
Diffuse neutron scattering is a valuable tool to obtain information about the size and orientation of the polar nanoregions that are a characteristic feature of relaxor ferroelectrics. In this paper, we present new diffuse scattering results obtained on Pb(Zn1/3Nb2/3)O3 (PZN for short) and (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT)single crystals (with x=4.5 and 9%), around various Bragg reflections and along three symmetry directions in the [100]-[011] zone. Diffuse scattering is observed around reflections with mixed indices, (100), (011) and (300), and along transverse and diagonal directions o…
Temperature dependent studies of the 1/2(hk0) superlattice reflections αspots by synchrotron x-ray scattering measurements were performed in (PMN) and (PMN-xPT) with Ti doping x<0.32 single crystals. Separation of the αspots from the underlying diffuse scattering background allowed studying them as separate entities for the first time. Structure factor calculations have shown that alpha spots constitute the presence of a new kind of anti-ferrodistortive nanoregions (AFR) in the form of fluctuations produced by anti-parallel short-range correlated <110> Pb^2+ displacements. AFR appear to be dif…
We present here the results of frequency dependent dielectric, polarization and powder X-ray powder diffraction studies in the 300 to 100K temperature range for Ba_0.55Sr_0.45TiO_3. The dielectric results indicate a succession of three relaxor ferroelectric transitions accompanying the cubic to tetragonal to orthorhombic to rhombohedral phase transitions confirmed by XRD studies. Our results confirm the coexistence of the relaxor ferroelectric and ferroelectric behaviours.
A key to optimizing the growth of the new single-crystal relaxor ferroelectrics is resolving basic questions concerning their structural properties and energetics. We report on initial first-principles total energy and force calculations, examining the energetics of local order in PZN type relaxors.
Relaxor ferroelectrics are complex materials with distinct properties different from classic ferroelectrics. Probing frequency depended dielectric susceptibility is its trait. Other empirical laws build on classic ferroelectrics are still applicable to relaxor ferroelectrics. Here we report an abnormal improved dielectric in La doped relaxor ferroelectric 0.4PNN-0.6PHT, which deviated from the consistent variation relationship with piezoelectric coefficient. A mesoscale mechanism is proposed to reveal the origin of the improved dielectric response in 0.4PNN-0.6PHT, where the polar nanoregions …
New relaxor ferroelectric system has been synthesized. BLTN exhibits a smeared maximum of permittivity, characteristic of classic relaxor behaviour, with a peak shift from 185 K at 100 Hz to 300 K at 1 GHz. BNTN undergoes a first order ferroelectric phase transition at 389 K and BLNTN exhibits both a ferroelectric phase transition at 274 K and relaxor behaviour at higher temperatures.
The polarization and strain response of ferroelectric materials at fields below the macroscopic coercive field is of a paramount importance for the operation of many electronic devices. The response of real ferroelectric and related materials is in general complex and difficult to interpret. The reason for this is that many processes in a ferroelectric material contribute to its properties, often concurrently. Examples include motion of ferroelectric and ferroelastic domains, presence of domains within domains, dynamics of different types of polar nano-entities, interaction of polar nano-entit…
A first-principles-based model is developed to investigate the influence of lead vacancies on the properties of relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 (PSN). Lead vacancies generate large, inhomogeneous, electric fields that reduce barriers between energy minima for different polarization directions. This naturally explains why relaxors with significant lead vacancy concentrations have broadened dielectric peaks at lower temperatures, and why lead vacancies smear properties in the neighborhood of the ferroelectric transition in PSN. We also reconsider the conventional wisdom that lead vacancie…
SrNaBi2Nb3O12 powder was prepared via the conventional solid-state reaction method. X-ray structural studies confirmed the phase to be a three-layered member of the Aurivillius family of oxides. SrNaBi2Nb3O12 (SNBN) ceramics exhibited the typical characteristics of relaxor ferroelectrics, associated with broad and dispersive dielectric maxima. The variation of temperature of dielectric maxima (Tm) with frequency obeyed the Vogel-Fulcher relationship. Relaxor behavior was believed to be arising from the cationic disorder at A-site. Pinched ferroelectric hysteresis loops were observed well above…
Inelastic neutron scattering study of the perovskite relaxor ferroelectric PZN:8%PT elucidates the origin of the previously reported unusual kink on the low frequency transverse phonon dispersion curve (known as "waterfall" effect). We show that its position depends on the choice of the Brillouin zone and that the relation of its position to the size of the polar nanoregions is highly improbable. The observation is explained in the framework of a simple model of coupled damped harmonic oscillators representing the acoustic and optic phonon branches.
We suggest a random field based model for calculation of physical properties of mixed ferroelectric relaxors. Our model naturally incorporates the different orientations of electric dipoles (related to different solid solution components) as well as the contribution of nonlinear and correlation effects of random field. We calculate the transition temperature $T_c$ as well as concentrational and temperature dependence of order parameters.
High energy resolution neutron spin-echo spectroscopy has been used to measure intrinsic width of diffuse scattering discovered earlier in relaxor ferroelectric crystals. The anisotropic and transverse components of the scattering have been observed in different Brillouin zones. Both components are found to be elastic within experimental accuracy of 1 eV. Possible physical origin of the static-like behavior is discussed for each diffuse scattering contribution.
We have measured the bending-induced polarization of Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals with compositions at the relaxor-ferroelectric phase boundary. The crystals display very large flexoelectricity, with flexocoupling coefficients an order of magnitude bigger than the theoretical upper limit set by the theories of Kogan and Tagantsev. This enhancement persists in the paraphrase up to a temperature T* that coincides with the start of elastic softening in the crystals. Analysis of the temperature dependence and cross-correlation between flexoelectric, dielectric and elastic properties ind…
A mechanically coupled phase-field model is proposed for the first time to simulate the peculiar behavior of relaxor ferroelectrics. Based on the random field theory for relaxors, local random fields are introduced to characterize the effect of chemical disorder. This generic model is developed from a thermodynamic framework and the microforce theory and is implemented by a nonlinear finite element method. Simulation results show that the model can reproduce relaxor features, such as domain miniaturization, small remnant polarization and large piezoelectric response. In particular, the influen…
Raman scattering in relaxor ferroelectric PbMg1/3Ta2/3O3 (PMT) was investigated in the single crystalline form in the temperature range of 20 - 295 K. Anomalous temperature dependence of the integrated intensity and the Raman line contours were found at the diffuse phase transition. A correlation between the anomalies in the integrated intensities and the dispersion of the dielectric response was observed. The distortions of Raman lines with decreasing temperature are discussed.
Ba(Zr,Ti)O$_3$ is a lead-free relaxor ferroelectric. Using the first-principles method, the ferroelectric dipole moments for pure BaTiO$_3$ and Ba(Zr,Ti)O$_3$ supercells have been studied. All possible ion configurations of BaZr$_{0.5}$Ti$_{0.5}$O$_3$ and BaZr$_{0.25}$Ti$_{0.75}$O$_3$ are constructed in a $2\times2\times2$ supercell. For the half-substituted case, divergence of ferroelectric properties has been found among these structures, which seriously depends on the arrangement of Ti and Zr ions. Thus our results provide a reasonable explanation to the relaxor behavior of Ba(Zr,Ti)O$_3$. …
The crystal structure of the PbMg$_{1/3}$Ta$_{2/3}$O$_3$ (PMT) relaxor ferroelectric was studied under hydrostatic pressure up to $\sim 7$ GPa by means of powder neutron diffraction. We find a drastic pressure-induced decrease of the lead displacement from the inversion centre which correlates with an increase by $\sim$ 50 % of the anisotropy of the oxygen temperature factor. The vibrations of the Mg/Ta are, in contrast, rather pressure insensitive. We attribute these changes being responsible for the previously reported pressure-induced suppression of the anomalous dielectric permittivity and…
An atomistic effective Hamiltonian is used to investigate electrocaloric (EC) effects of Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ (PMN) relaxor ferroelectrics in its ergodic regime, and subject to electric fields applied along the pseudocubic [111] direction. Such Hamiltonian qualitatively reproduces (i) the electric field-versus-temperature phase diagram, including the existence of a critical point where first-order and second-order transitions meet each other; and (ii) a giant EC response near such critical point. It also reveals that such giant response around this critical point is microscopically …
Epitaxial thin films of relaxor PbMg1/3Nb2/3O3 and PbSc0.5Nb0.5O3, and ferroelectric PbZr0.65Ti0.35O3, Pb0.955La0.045Zr0.65Ti0.35O3, and Ba0.4Sr0.6TiO3 were prepared, and their dielectric properties were studied in a broad range of the measurement conditions. In the ferroelectric state, the presence and the change of configuration of the domains determined both the dynamic dielectric nonlinearity and the polarization hysteresis. In thin-film relaxors, the orientation of the randomly interacting dipoles in a random field was responsible for the dynamic dielectric nonlinearity, while the observe…
The model for calculation of relaxor ferroelectrics thin films properties is proposed. The basis of the model is the theory of random field. This field is originated from the chemical disorder allowing for influence of the film surfaces, which destroys the polar long-range order and transform it into mixed state of ferroelectric glass (FG) or dipole glass (DG). The spatial profiles and averaged over coordinate inside the film values of properties of relaxor ferroelectric film were calculated with the random field distribution function. As an example the dependence of the order parameter on fil…
Relaxor ferroelectrics are complex oxide materials which are rather unique to study the effects of compositional disorder on phase transitions. Here, we study the effects of quenched cubic random electric fields on the lattice instabilities that lead to a ferroelectric transition and show that, within a microscopic model and a statistical mechanical solution, even weak compositional disorder can prohibit the development of long-range order and that a random field state with anisotropic and power-law correlations of polarization emerges from the combined effect of their characteristic dipole fo…
We have recently observed a giant electrocaloric effect (12 K in 25 V) in 350 nm sol-gel Pb Zr_0.95 Ti_0.05 O_3 films near the ferroelectric Curie temperature of 242oC. Here we demonstrate a giant electrocaloric effect (5 K in 25 V) in 260 nm sol-gel films of the relaxor ferroelectric 0.9 PbMg_(1/3)Nb_(2/3)O_3 - 0.1 PbTiO_3 near the Curie temperature of 60oC. This reduction in operating temperature widens the potential for applications in novel cooling systems.
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 one 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 K < 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 Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in the develop…
CuCrS2, a Heisenberg antiferromagnet with layered edge sharing triangular lattice, exhibits a spiral magnetic order. Dielectric (E) and polarization studies show magnetoelectric (ME) coupling at Neel temperature (T_N=38 K) where simultaneous dielectric and magnetic long range order occur. The compound shows a diffused ferroelectric (FE) transition and slow relaxation dynamics above T_N, indicative of relaxor FE behavior. Interestingly, memory effect and magnetic field induced rejuvenation are also observed in E, establishing cooperative glassy dynamics and ME coupling even above T_N. We discus…
Herein, we elucidate the impact of tubular confinement on the structure and relaxation behaviour of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like -relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strickingly, both the bulk-like and the i…
Ferroelectric domain structure evolution induced by an external electric field was investigated by means of nematic liquid crystal (NLC) method in two strontium-barium niobate single crystals of nominal composition: Sr_{0.70}Ba_{0.30}Nb_{2}O_{6} (SBN:70 - relaxor) and Sr_{0.26}Ba_{0.74}Nb_{2}O_{6} (SBN:26 - ferroelectric). Our results provide evidence that the broad phase transition and frequency dispersion that are exhibited in SBN:70 crystal have a strong link to the configuration of ferroelectric microdomains. The large leakage current revealed in SBN:26 may compensate internal charges acti…
Neutron and x-ray scattering studies on relaxor ferroelectric systems Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN), Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$ (PMN), and their solid solutions with PbTiO$_3$ (PT) have shown that inhomogeneities and disorder play important roles in the materials properties. Although a long-range polar order can be established at low temperature - sometimes with the help of an external electric field; short-range local structures called the ``polar nano-regions'' (PNR) still persist. Both the bulk structure and the PNR have been studied in details. The coexistence and competition of l…
We have characterized the dynamics of the polar nanoregions in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ (PMN) through high-resolution neutron backscattering and spin-echo measurements of the diffuse scattering cross section. We find that the diffuse scattering intensity consists of \emph{both} static and dynamic components. The static component first appears at the Curie temperature $Θ\sim 400$ K, while the dynamic component freezes completely at the temperature T$_{f} \sim 200$ K; together, these components account for all of the observed spectral weight contributing to the diffuse scattering cross se…
Synchrotron x-ray scattering studies of anti-ferroelectric nanoregions (AFR) as fluctuations, which give rise to 1/2(hk0) superlattice reflections (alpha spots), were systematically performed in Pb(Mg1/3Nb2/3)O3 (PMN) ferroelectric relaxor. Separation of the alpha spots from underlying diffuse scattering background allowed studying them as separate entities for the first time. AFR fluctuations were shown to be different from the chemical nanodomains (CND) and ferroelectric polar nano-regions (PNR). Instead, they are formed by anti-parallel short-range correlated Pb^2+ displacements that lead t…
A review is given of the phonon anomalies, which have been termed ``waterfalls,'' that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions.
Spatial variability of polarization relaxation kinetics in relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved Piezoresponse Force Microscopy. Local relaxation attributed to the reorientation of polar nanoregions is shown to follow stretched exponential dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the macroscopic value determined from dielectric spectra (beta~~0.09). The spatial inhomogeneity of relaxation time distributions with the presence of 100-200 nm "fast" and "slow" regions is observed. The results are analyzed to map the Vogel-Fulcher…
The comparative experimental analysis of polarization reversal kinetics in conventional homogeneous triglycine sulfate ((NH_{2}CH_{2}COOH)_{3} \cdot H_{2}SO_{4}; TGS) and relaxor strontium barium niobate (Sr_{0.61}Ba_{0.39}Nb_{2}O_{6}; SBN) crystals have been performed in a broad range of measurement conditions. The experimental data have been collected from microscopic observation of the domain structure, switching current and D-E hysteresis loop registration. The hysteresis loop and dielectric spectra have a strong link to the configuration of ferroelectric microdomains. The domain structure…
The low-energy part of vibration spectrum in PbMg$_{1/3}$Nb$_{2/3}$O$_3$ relaxor ferroelectric was studied by inelastic neutron scattering. We observed the coexistence of a resolution-limited central peak with strong quasielastic scattering. The line-width of the quasielastic component follows a $Γ_0+Dq^2$ dependence. We find that $Γ_0$ is temperature-dependent. The relaxation time follows the Arrhenius law well. The presence of a relaxation mode associated with quasi-elastic scattering in PMN indicates that order-disorder behaviour plays an important rôle in the dynamics of diffuse phase tran…
We report the spontaneous decay of a soft, optical phonon in a solid. Using neutron spectroscopy, we find that specific phonon lifetimes in the relaxor PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ are anomalously short within well-defined ranges of energy and momentum. This behavior is independent of ferroelectric order and occurs when the optical phonon with a specific energy and momentum can kinematically decay into two acoustic phonons with lower phase velocity. We interpret the well-known relaxor "waterfall" effect as a form of quasiparticle decay analogous to that previously reported in quantum spin liq…
(1-x)Li0.12Na0.88NbO3-xBaTiO3 (0 to x to 0.40) ferroelectric ceramics were prepared using conventional ceramics route and their phase transitional behavior is investigated by using dielectric spectroscopy. The temperature-dependent dielectric permittivity epsilon'(T) shows a diffused ferroelectric-paraelectric transition for all compositions. An acceptable and competent characterizing parameter (D) of diffused phase transition (DPT), defined by Uchino et al. [J Am Ceram Soc 2010;93:4011], was measured and validated. Interestingly, a crossover from diffused ferroelectric phase transition (FE-DP…
Neutron elastic diffuse scattering experiments performed on Pb(Zn1/3Nb2/3)O3 (PZN) and on its solid solution with PbTiO3(PT), known as PZN-xPT, with x=4.5% and 9% around many reflections show that diffuse scattering is observed around reflections with mixed indices in the transverse and diagonal directions only. From the width of the diffuse scattering peak a correlation length is extracted. In PZN, we have reported that the diffuse scattering is more extended in the transverse than in the diagonal directions. In the present work, the results show that the addition of PT leads to a broadening …
Neutron inelastic scattering measurements of the polar TO phonon mode dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal anomalous behavior in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q=0.2 inverse Angstroms, measured from the zone center. We speculate this behavior is the result of nanometer-sized polar regions in the crystal.
Short-range polar orders in the relaxor ferroelectric material PbMg$_{1/3}$Nb$_{2/3}$O$_3$-$28\%$PbTiO$_3$ (PMN-28PT) have been studied using neutron diffuse scattering. An external electric field along [110] direction can affect the diffuse scattering in the low temperature rhombohedral/monoclinic phase. Diffuse scattering intensities associated with [110] short-range polarizations are partially suppressed, while those arising from [1$\bar{1}$0] polarizations are enhanced. On the other hand, short-range polar orders along other equivalent $\langle110\rangle$ directions, i.e. [101],[10$\bar{1}…
Barkhausen current noise is used to probe the slow field-driven conversion of the glassy relaxor ferroelectric state to an ordered ferroelectric (FE) state. The frequent presence of distinct micron-scale Barkhausen events well before the polarization current starts to speed up shows that the process is not a conventional nucleation-limited one. The prevalence of reverse switching events near the onset of the rapid part of the transition strongly indicates that electric dipole interactions play a key role. The combination of Barkhausen noise changes and changes in the complex dielectric respons…
We report high $q$-resolution neutron scattering data on PMN-$x$PT single crystals with $x=20%$ and 27%. No rhombohedral distortion occurs in the 20PT sample for temperatures as low as 50 K. On the other hand, the 27PT sample transforms into a rhombohedral phase below T$_C \sim 375$ K. Our data provide conclusive evidence that a new phase with an average cubic lattice is present in the bulk of this relaxor system at low PT concentration, in which the ferroelectric polarization and lattice distortion are decoupled. The rhombohedral distortion is limited to the outermost tens of microns of the c…
The radiofrequency dielectric response of the lead-free Ba(Zr$_{0.5}$Ti$_{0.5}$)O$_3$ relaxor ferroelectric is simulated using a coarse-grained Hamiltonian. This concept, taken from Real-Space Renormalization Group theories, allows depicting the collective behavior of correlated local modes gathered in blocks. Free-energy barriers for their thermally activated collective hopping are deduced from this {\it ab-initio}-based approach, and used as input data of Kinetic Monte Carlo simulations. The resulting numerical scheme allows to simulate the dielectric response for external field frequencies …
A novel lead-free tungsten bronze type ceramic Sr5BiTi3Nb7O30, was prepared by a conventional solid-state reaction route. The room-temperature crystal structure shows an average structure with centro-symmetric space group P4/mbm identified by synchrotron XRD. Temperature dependence of dielectric permittivity indicates that Sr5BiTi3Nb7O30 is a ferroelectric relaxor with Tm near 260 K. The ceramic displays stronger frequency dispersion and lower phase-transition temperature compared with Sr6Ti2Nb8O30. A macroscopic and phenomenological statistical model was employed to describe the temperature d…
We present first-principles supercell calculations on BaTi0.74Zr0.26O3, a prototype material for relaxors with a homovalent substitution. From a statistical analysis of relaxed structures, we give evidence for four types of Ti-atom polar displacements: along the < 1 1 1 >, < 1 1 0 >, or < 1 0 0 > directions of the cubic unit cell, or almost cancelled. The type of a Ti displacement is entirely determined by the Ti/Zr distribution in the adjacent unit cells. The underlying mechanism involves local strain effects that ensue from the difference in size between the Ti4+ and Zr4+ cations. These resu…
For the first time we proposed the model for the calculations of the relaxor ferroelectrics films properties in the framework of the random field theory. We took into account the misfit strain between film and substrate as well as surface piezoelectric effect that causes built-in electric field in the strained films. In the statistical theory framework we calculated random field distribution function with the electric dipoles and monopoles as the field sources. It was shown that with thickness decrease the mean field decreases, while the width of the distribution function increases. This leads…
Ferroelectric relaxors are complex materials with distinct properties. The understanding of their dielectric susceptibility, which strongly depends on both temperature and probing frequency, have interested researchers for many years. Here we report a macroscopic and phenomenological approach based on statistical modeling to investigate and better understand how the dielectric response of a relaxor depends on temperature. Employing the Maxwell-Boltzmann distribution and considering temperature dependent dipolar orientational polarizability, we propose a minimum statistical model and specific e…
Neutron scattering measurements of the lowest-energy TO phonons in the relaxor Pb(Mg1/3Nb2/3)O3 (PMN) are reported for 10<=T<=750 K. The soft mode, which is overdamped by the polar nanoregions below the Burns temperature T_d = 620 K, surprisingly recovers below 220 K. The square of the soft mode energy hw0^2 increases linearly with decreasing temperature, and is consistent with the behavior of a ferroelectric soft mode. At 10 K, hw0 reaches 11 meV, the same value observed in ferroelectric Pb(Zn1/3Nb2/3)O3 at low-T. An unusual broadening of the TA phonon starts at T_d and disappears at 220 K, c…
Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling are some of the most important functional materials with applications ranging from ultrasound imaging to actuators and sensors in microelectromechanical devices. Since their discovery nearly 60 years ago, the complexity of nanoscale chemical and structural heterogeneity in these systems has made understanding the origins of their unique electromechanical properties a seemingly intractable problem. A full accounting of the mechanisms that connect local structure and chemistry with nanoscale fluctuations in polariza…
An atomistic first-principles-based effective Hamiltonian is used to investigate energy storage in Ba(Zr$_{0.5}$Ti$_{0.5}$)O$_{3}$ relaxor ferroelectrics, both in their bulk and epitaxial films' forms, for electric fields applied along different crystallographic directions. We find that the energy density linearly increases with temperature for electric fields applied along the pseudocubic [001], [110] and [111] directions in Ba(Zr$_{0.5}$Ti$_{0.5}$)O$_{3}$ bulk. For films at room temperature, the energy density adopts different behaviors (i.e., increase versus decrease) with strain depending …
