Relaxor Ferroelectric Materials Research Articles

Scanning probe microscopy investigation of ferroelectric properties of barium strontium niobate crystals

The ferroelectric properties of relaxor ferroelectric materials Sr x Ba1 − x Nb2O6 of different compositions have been investigated using scanning probe microscopy and macroscopic polarization methods. An analysis of the results obtained from microscopic and macroscopic measurements of the hysteresis loops has demonstrated that a frequency dependence of the coercive field E c is observed at frequencies f in the range from 0.03 to 250 Hz, so that the coercive field E c regularly decreases with decreasing frequency. The observation of the kinetics of domains under a direct-current voltage applied to the probe of the atomic force microscope has revealed a lateral motion of domain walls in response to electric fields E ≪ E c . This result qualitatively explains a slow polarization relaxation occurring for a giant time in Sr x Ba1 − x Nb2O6.

Probing local polar structures in PZN-xPT and PMN-xPT relaxor ferroelectrics with neutron and x-ray scattering

"Polar nano-regions" (PNR) are nanometer sized local polar structures found in relaxor ferroelectric materials. They play key roles in understanding many relaxor properties. Here I will discuss some of our recent work using neutron scattering and x-ray diffraction to probe the properties of the PNR in two prototypical lead based perovskite relaxor systems Pb(Zn1/3Nb2/3)O3 (PZN), Pb(Mg1/3Nb2/3)O3 (PMN), and their solid solutions with PbTiO3 (PT). The local atomic structures in the PNR are rather complicated, consisting of polarizations/atomic shifts along both ⟨110⟩ and ⟨100⟩ directions. These different (components of) local polarizations respond differently to external electric fields along [001] or [111] directions; and are associated with phonons of different polarizations (T1 and T2 phonon modes). Our work also indicates that the PNR are dynamic at high temperatures well above the Curie temperature TC, and gradually freeze with cooling. A significant portion of the PNR has already become static before a long-range polar order can be established in the bulk. The short-range polar order in the PNR is quite robust, and persists when the system is cooled (with or without external electric field) into the ferroelectric phase. Because of the frustration between charge neutrality and lattice strain in relaxor systems, the low temperature phase of these relaxor materials usually does not have perfect long-range order, but rather a phase where both short-range and long-range polar orders coexist and compete.

Investigating the physical meanings of diffused phase transition models

The empirical laws, ɛ = ɛ m/[1 + ( T − T m) γ /2 σ 2] and ɛ = ɛ m/{1 + [( T − T m)/ Δ] ξ }, proposed by Burfoot et al. and Eiras et al. are usually used to describe the dielectric diffused characteristics of relaxor ferroelectric materials. In this study, we continue our previous work to present the physical and mathematical meanings of the parameters in these laws. Based on the experimental results in the (1 − x)Pb(Fe 2/3W 1/3)O 3– xPbTiO 3 relaxor system and theoretical modelling analysis, it is shown that the law proposed by Eiras is more suitable to explain the behaviour of both more complete relaxor systems and incomplete relaxor systems.

Two-component model of the neutron diffuse scattering in the relaxor ferroelectric PZN-4.5%PT

We report measurements of the neutron diffuse scattering in a single crystal of the relaxor ferroelectric material 95.5%Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$-4.5%PbTiO$_3$ (PZN-4.5%PT). Our results suggest that the nanometer scale structure in this compound exhibits both $<100>$ and $<110>$ polarizations, which contribute to different portions of the total diffuse scattering intensity. These contributions can be distinguished by the differing responses to an electric field applied along [001]. While diffuse scattering intensities associated with $<110>$ (T2-type) polarizations show little to no change in a [001] field, those associated with $<100>$ (T1-type) polarizations are partially suppressed by the field at temperatures below the Curie temperature \emph{T$_C$} $\sim 475$ K. Neutron spin-echo measurements show that the diffuse scattering at (0.05,0,1) is largely dynamic at high temperature and gradually freezes on cooling, becoming mostly static at 200 K.

ChemInform Abstract: New Preparation Method of Low-Temperature-Sinterable Perovskite 0.9Pb(Mg1/3Nb2/3) O3-0.1PbTiO3 Powder and Its Dielectric Properties.

A relaxor ferroelectric material, 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (0.9PMN-0.1PT) with a pyrochlore-free phase, was prepared by using one-step calcination in the present study. The 0.9PMN-0.1PT powder with the pure perovskite phase was prepared successfully from a mixture of the PMN precursor and the crystalline PT by heating for 2 h at temperatures greaterthan equal to750°C. The PMN precursor was synthesized by adding an aqueous Mg(NO3)2 solution, rather than MgO, to the alcoholic slurry of PbO and Nb2O5. The 0.9PMN-0.1PT powder sintered to >96% relative density via heat treatment for 2 h at temperatures of 900°-1200°C. The highest room-temperature dielectric constant (epsilonrt) was 24700 at 1 kHz for the samples that were sintered at 1100°C; however, the samples that were sintered at 900°C still had epsilonrt values of 22600 at 1 kHz.

A Vibration-Based PMN-PT Energy Harvester

We report design, modeling, analysis, and experimental study of a vibration-based piezoelectric energy harvester. The energy harvester is made of a composite cantilever of a single crystal relaxor ferroelectric material, (1- x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), and a polydimethylsiloxane (PDMS) base layer. A PDMS proof mass is constructed at the tip of the composite cantilever beam and is used as a means to tune the system natural frequency. The use of the PMN-PT piezoelectric material and an interdigited electrodes (IDEs) design improves the energy conversion efficiency. A dynamic systems modeling approach is employed to analyze the responses and the performance of the harvester design. We have demonstrated that a prototype of the harvester with a size of 7.4 mm times 2 mm times 110 mum outputs a voltage of 10 V (0.3 mW power) under a vibration excitation with a peak-to-peak amplitude of 1 mm at a frequency around 1.3 kHz. Based on the experimental results, the power density prediction of the proposed harvester design shows a superior performance than that of the other reported piezoelectric harvesters.

Magnetic glassy behavior in ferroelectric relaxor type solid solutions: Magnetoelectric relaxor

Perovskite solid solution ceramics with compositions of 0.9Pb(Fe0.5Nb0.5)O3–0.1PbTiO3, 0.6Pb(Ni1∕3Nb2∕3)O3–0.4PbTiO3, and 0.6Pb(Co1∕3Nb2∕3)O3–0.4PbTiO3 were synthesized by the traditional solid state reaction method. Ferroelectric measurements revealed that these samples have well saturated polarization-electrical field loops. Dielectric measurements showed that abnormal dielectric peaks at their Curie temperature were frequency dependent. Both characteristics indicate that these samples are relaxor type ferroelectric materials. Field cooled and zero field cooled magnetization measurements revealed that the 0.6Pb(Ni1∕3Nb2∕3)O3–0.4PbTiO3 and 0.6Pb(Co1∕3Nb2∕3)O3–0.4PbTiO3 samples are paramagnetic down to 5K, while the 0.9Pb(Fe0.5Nb0.5)O3–0.1PbTiO3 sample shows an antiferromagnetic-like ordering starting from around 40K. Furthermore, a weak ferromagnetism is observed in the 0.9Pb(Fe0.5Nb0.5)O3–0.1PbTiO3 sample, as evidenced by the magnetic hysteresis loop measured at 10K. The ac susceptibility measurement of this sample showed that the peak position around 40K is strongly dependent on frequency, indicating a glassy or relaxor type bahavior below that temperature. Therefore, relaxor type ferroelectric and magnetic 0.9Pb(Fe0.5Nb0.5)O3–0.1PbTiO3 is a magnetoelectric relaxor.

Neutron scattering study of the relaxor ferroelectric K 1−xLi xTaO 3

Neutron scattering experiments using triple axis spectrometers have been performed for the relaxor ferroelectric materials K 1− x Li x TaO 3 ( x=0.05, 0.10) in order to study the behavior of the zone-center (ZC) transverse-optic (TO) phonon mode (ferroelectric mode). A major contrast between the x=0.05 and 0.10 samples is the ferroelectric transition-observed only for the latter material at T C =115 K on warming and as detected by dielectric measurements and neutron diffraction. The ZC TO mode for x=0.05 shows monotonic softening with decreasing temperature down to 10 K, whereas the x=0.10 sample shows a phonon component below T C which hardens with decreasing temperature in addition to a phonon mode which behaves similarly to that of the x=0.05 sample. This suggests a phase separation of the x=0.10 sample into ferroelectric and relaxor states below T C , possibly originating from a percolative nature of the ferroelectric state.

Effects of Oxygen Annealing on Dielectric Properties of LuFeCuO4

We investigated the effect of oxygen annealing on dielectric properties of LuFeCuO4 mainly by dielectric measurements and transmission electron microscopy experiments. It was found that the leakage current density decreases with high-pressure oxygen annealing and the size of nanodomains with orientational polarization increases, which is characterized by the short-range ordering of Fe3+ and Cu2+ ions on a triangular lattice. In addition, the absolute value of relative permittivity ε' decreases with oxygen annealing and ε' exhibits a broad peak in the temperature window between room temperature and 550 K, which is similar to that observed in relaxor ferroelectric materials. The present experimental results suggest that the number of oxygen vacancies has a crucial effect on dielectric properties of LuFeCuO4.

Dynamic origin of the morphotropic phase boundary: Soft modes and phase instability in0.68Pb(Mg1/3Nb2/3O3)−0.32PbTiO3

We report neutron inelastic scattering and high-resolution x-ray diffraction measurements on single crystal $0.68\text{Pb}({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}{\text{O}}_{3})\text{\ensuremath{-}}0.32{\text{PbTiO}}_{3}$ (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB) where the piezoelectric properties of $\text{PMN-}x\text{PT}$ compounds are close to maximal. Data were obtained between 100 and 600 K under zero and nonzero electric field applied along the cubic [001] direction. The lowest-energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however, the square of the soft-mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft-mode ``recovery,'' upon cooling into the tetragonal phase at ${T}_{C}$. Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no well-defined structural transition (no ${T}_{C}$). The temperature dependence of the soft mode in PMN-0.32PT is also similar to that in PMN-0.60PT; however, in PMN-0.60PT the recovery temperature equals ${T}_{C}$. These results suggest that the temperature dependence and the energy scale of the soft-mode dynamics in $\text{PMN-}x\text{PT}$ are independent of concentration on the Ti-poor side of the MPB, but scale with ${T}_{C}$ for Ti-rich compositions. Thus the MPB may be defined in lattice dynamical terms as the concentration where ${T}_{C}$ first matches the recovery temperature of the soft mode. High-resolution x-ray studies show that the cubic-to-ferroelectric phase boundary shifts to higher temperatures by an abnormal amount within the MPB region in the presence of an electric field. This suggests that an unusual instability exists within the apparently cubic phase at the MPB.

Preparation of the Pb(Mg 1/3Nb 2/3)O 3 films by aqueous tape casting

Lead magnesium niobate (PMN) is a relaxor ferroelectric material. Because of its high dielectric constant and superior electrostrictive properties it is commonly used in the manufacture of multilayer electronic devices which is typically produced by tape casting. However, preparation of PMN slurry formulations to use in aqueous tape casting process is not investigated in detail yet. Therefore, in this study aqueous PMN formulations were developed for tape casting and its relation with the final properties of PMN films were investigated. The slurries were prepared using poly(acrylic acid)-based comb polymer as the dispersant, nonionic acrylic latex as the binder and the hydroxypropyl methyl cellulose as the wetting agent. The results showed that it is possible to prepare flexible, crack-free PMN films using highly concentrated suspensions without using any plasticizer. The study gives guidelines for the aqueous tape casting of PMN and can be adapted to processing of other multi-component metal oxides.

Diffuse Scattering and Monte Carlo Studies of Relaxor Ferroelectrics

A renewed interest in the field of ferroelectricity has taken place in recent years since the finding of exceptional piezoelectric properties in the lead-oxide class of relaxor ferroelectric materials typified by the disordered perovskite PbZn1/3Nb2/3O3 (PZN). Although PZN and numerous related materials have been extensively studied over a long period, a detailed understanding of the exact nature of their polar nanostructure has still not emerged. In this article, we describe the development of Monte Carlo computer models, which seek to account for the detailed three-dimensional (3-D) diffuse neutron scattering data that have been recorded from a single crystal of PZN. It has been established that the observed diffuse patterns are due to planar nanodomains oriented normal to the six \( \left\langle {{\text{110}}} \right\rangle \) directions, but there is still some uncertainty concerning the direction of the local Pb ionic shifts, which remains an area of controversy. It is argued that further detailed analysis and experiments in which data are recorded with the crystal in an applied field should allow these remaining issues to be resolved.

Phase instability induced by polar nanoregions in a relaxor ferroelectric system

Relaxor ferroelectrics are a special class of material that exhibit an enormous electromechanical response and are easily polarized with an external field. These properties make them attractive for applications as sensors and actuators. Local clusters of randomly oriented polarization, known as polar nanoregions (PNRs), are specific to relaxor ferroelectrics and play a key role in governing their dielectric properties. Here, we show through neutron inelastic scattering experiments that the PNRs can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3)-4.5%PbTiO(3) (PZN-4.5%PT). A strong interaction is found between the PNRs and the propagation of acoustic phonons. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNRs. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results naturally explain the emergence of the various observed monoclinic phases in these systems.

Rheological behavior of PMN gels for solid freeform fabrication

Lead magnesium niobate (PMN) is a relaxor ferroelectric material and have widespread applications in the manufacture of multilayer electronic devices such as ceramic capacitors, actuators and transducers. The dielectric constant of this electrostrictive material is much higher than the well known ferroelectric barium titanate. However, aqueous processing of PMN is not investigated yet especially for the novel wet shaping fabrication. In this study, concentrated aqueous colloidal PMN gels have been designed to use in the robocasting process. Concentrated PMN suspensions were stabilized by polyacrylic acid and then gelation induced by changing the pH or ionic strength of the suspension or by addition of a cationic polyelectrolyte to the system. Through this procedure it was essential to understand the solid–liquid transition under shear to explore the feasibility of forming without excessive use of polymers. Therefore, rheological response of the samples having a gel network was investigated. Results showed that gelation induced by cationic polyethylene imine or by multivalent salts were successful methods in preparation of PMN gels. However, gelation induced by changing the pH of the suspension was challenging due to ion dissolution from PMN surface.

Solubility and aging of lead magnesium niobate in water

Lead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly employed in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, stability of this material in water is not very well known and there is need for a detailed investigation. In this research, solubility of lead magnesium niobate powders in water was determined as a function of solids concentration. The obtained results showed that the amount of cation leaching from the PMN surface depends on the pH value of the suspension and the solids concentration. The Pb 2+ and Mg 2+ ion dissolution was very high especially in the acidic pH range. Nevertheless, neither the dissolution mechanism nor the effects of dissolved ions on the stability were the same for those ions. The study provides new aspects on the solubility of perovskite materials which possess more than one soluble cation in their structure.

Pb(Mg1/3Nb2/3)O3-based 강유전체의 상전이 및 완화특성

Dielectric and pyroelectric properties of relaxor ferroelectric in the PMN-PT solid solution series have been investigated. Features of the diffuse phase transition in PMN-PT system, typical relaxor ferroelectric materials, were studied as a function of temperature and frequency. The transition temperature of the ceramics with PT~0.325 did not depend on the measuring frequency. This can best realized in a relatively random environment that apparently is provided by PMN-rich complex perovskites, including those containing Pb. The composition with PT＞0.35 show the characteristics of a normal single phase ferroelectric material. Thus the studies revealed that the morphotropic phase boundary in the PMN-PT system is in the vicinity of PT~0.3 and it has a small curvature and as a result the compositions near the morphotropic phase boundary show two phase transitions, rhombohedral→tetragonal→cubic, when the samples are heated up to higher temperature. The best optimum compositions are observed near the morphotropic phase boundary.

Dynamical properties of the relaxor ferroelectric 0.71Pb(Ni/sub 1/3/Nb/sub 2/3/)O/sub 3/-O.29PbTiO/sub 3/ probed by brillouin and raman scattering

Abstract-Structural phase transitions in relaxor ferroelectric materials remain to be one of the most puzzling issues in materials science. In the present work, we have investigated relaxational and vibrational properties of a relaxor ferroelectric 0.71Pb(Ni(1/3)Nb(2/3))O(3)-O.29PbTiO(3) single crystal by means of inelastic light scattering measurements. Analysis based on the spectra has shown anomalous behaviors at Burns' temperature T(d), freezing temperature T(f) , those are related to a development of polar nanoregions (PNRs). The PNR must play a key role in the relaxor nature, and obtained results provide new insights into the relaxational dynamics in the PNRs and into how they develop below T(f).

Preparations and Characterizations of Perovskite PMN Ceramics by Using a One-Step Calcination Method

A relaxor ferroelectric material, Pb(Mg1/3Nb2/3)O3 (PMN) powder with a pyrochlore-free phase, was prepared by using a one-step calcinations method. The pyrochlore phase was prevented by coating Mg(OH)2 on Nb2O5 particles. Pure-perovskite PMN powder was synthesized by a single calcination of the coating powder mixed with appropriate amounts of PbO at 900 oC for 2 h. The pyrochlore-free perovskite PMN powders were sintered to 96.9% density at 1100 oC. The sintered PMN ceramics exhibited a dielectric constant maximum of ~11 700 at room temperature at a frequency of 1 kHz.

Dielectric and relaxor ferroelectric properties of Ba-doped Pb(Zr,Ti)O3 ceramics

(Pb,Ba)(Zr,Ti)O3 is a relaxor ferroelectric material. Dielectric and ferroelectric properties of (Pb1-xBax)(Zr0.70Ti0.30)O3 ceramics have been investigated for compositions varying in the range of 0.20 ≤ x ≤ 0.30. Reagent grade PbO, ZrO2, TiO2 and BaCO3 raw powders were used, ceramics were fabricated by convenient solid state reaction. The experimental results show that the substitution of Ba for Pb can enhance the ferroelectric relaxor characteristics. With the Ba content increasing, the electric hysteresis was narrowed and the polarization was reduced. Meanwhile the temperature Tm that corresponding to the maximal dielectric constant was decreased. It has also been found that the hydrostatic pressure may cause the phase transition more diffuse and move Tm to higher temperature.

Dielectric properties of PbNb2O6 ferroelectric ceramics at cryogenic temperatures

Complex dielectric permittivity measurements in PbNb2O6 ceramics were performed in a frequency and temperature range of 1kHz–1MHz and from 15to900K, respectively. The results revealed two dielectric anomalies showing typical characteristics of relaxor ferroelectric materials at cryogenic temperatures. Comparison with other tetragonal tungsten bronze (TTB) structure-type materials suggests the existence of successive phase transitions, which until now were not reported. The observed low temperature dielectric behaviors seem to be due to intrinsic physical characteristics related to the TTB structure.