Relaxor Compositions Research Articles

Contrasting phenomena of quenching-induced piezoelectric performance in (0.4Na1/2Bi1/2TiO3-0.6BiFeO3)-xBaTiO3 ferroelectrics and relaxors

Na1/2Bi1/2TiO3 (NBT)-based materials are promising lead-free alternatives due to their large electrostrain and stable mechanical quality factor. Nonetheless, the relatively low depolarization temperature (Td) impairs its practical application. Recently, quenching from sintering temperature was adopted to increase Td of NBT-based ceramics. However, the origin of the quenching-induced increase in Td is still debated. In this study, quenching effects in (1-x)(0.4Na1/2Bi1/2TiO3-0.6BiFeO3)-xBaTiO3 ceramics are investigated. With increasing BaTiO3 content, this system transforms from ferroelectric to relaxor state at room temperature, with a criticality at x = 0.07, which exhibits R3c and P4bm coexisted phases. Ferroelectric and relaxor compositions exhibit different responses upon quenching. Upon quenching the ferroelectrics, Td increases from 420 to 580 °C for x = 0.04, but d33 is majorly unaltered. However, upon quenching the relaxors, Td increases marginally, while d33 increases from 62 to 97 pC/N. The correlation between the structural evolution and electrical responses upon quenching ferroelectric and relaxor compositions is explored.

Disorder in Strontium Barium Niobate: Local Structure, Phonons, and Polarization Dynamics.

The main representative of the tetragonal tungsten bronze family, strontium barium niobate, has been recently studied by the scattering and spectroscopic techniques [diffuse scattering (DS), Raman, infrared, and high-frequency dielectric spectroscopies] to decipher the nature of its ferroelectric-relaxor transformation tuned by composition. DS revealed that mesoscopic range ordered correlations along the polar axis are presented in the crystal, being less organized in the relaxor compositions with higher Sr content. For these compositions, transverse polar correlations are found to be anisotropic. Pair distribution function experiments and first-principle calculations in several compositions showed a concomitant new peak around ~6.5 Å, which develops on cooling and cannot be explained by the current structural models with long-range incommensurate oxygen tilts but with a short-range ordered tilt arrangement. This relates with the development of the macroscopic polarization, tightly linked to the structure, and shows two different contributions related to the two different crystallographic sites for the ferroactive Nb atom, recalling a picture of two independent polarization networks showing disparate dynamics, temperature behavior, and correlation lengths. Cationic substitution in different channels affects mainly the relaxations. Above the MHz range, all members of the solid solutions show three main relaxations, whose temperature dependence is unalike, due to the distinct correlation lengths and nature of the processes. On increasing Sr content, the frequencies are higher, and the contribution to the permittivity of excitations at GHz-THz ranges gets stronger. A soft anharmonic central mode at THz range is the characteristic for all the compositions, together with the slowing down of a relaxation at GHz-MHz ranges, revealing the coexistence of displacive and order-disorder mechanisms of the ferroelectric phase transition in these solid solutions.

Re‐entrant ferroelectric relaxor phenomena in the (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3 system

AbstractThe solid solution (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3, (0.00 ≤ x ≤ 0.12) was investigated to examine the phase equilibria, dielectric and electromechanical properties. The composition corresponding to x = 0.00 exhibits tetragonal symmetry with the expected classical ferroelectric (FE) behavior. The system exhibited FE to relaxor crossover with the addition of lead zirconate at the composition x = 0.05. This is indicated by typical relaxor characteristics such as a transition to the global pseudocubic phase, a constriction in the FE hysteresis loop, and a sudden decrease in the negative strain accompanied by an increase in maximum strain. Most notably, with a further increase in x (>0.05), there is evidence for a return to a FE phase that exhibits classical FE characteristics. The combined results demonstrate that there exists a narrow FE‐relaxor boundary near x = 0.05, where FE and relaxor phases coexist. At the critical composition, enhancement in the piezoelectric properties, including an increase in the effective (350 pm/V) was observed. This transition in the electromechanical properties is consistent with changes observed in the phase equilibria for this solid solution. The crystal structure transitions from tetragonal symmetry for x = 0.00, to pseudocubic symmetry for the relaxor compositions (x = 0.05), and finally to a lower symmetry perovskite phase for the re‐entrant FE phase (x> 0.05). This composition‐induced transition from FE to relaxor to a re‐entrant FE state in the (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3 system is unusual among relaxor FE systems and thus is of great scientific and technological interest.

Dynamics of mesoscopic polarization in the uniaxial tetragonal tungsten bronze (SrxBa1−x)Nb2O6

The high-frequency dielectric behavior of uniaxial tungsten-bronze strontium barium niobate crystals with various Sr/Ba ratios, including both ferroelectric and relaxor compositions, have been studied in a broad frequency range (${10}^{4}$ to ${10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$) and temperature interval 100--500 K in order to thoroughly understand the evolution of the relaxation dynamics across the ferroelectric phase transition. The dielectric response along the polar axis consists of three relaxations corresponding to polarization mechanisms related to several correlation lengths of mesoscopic order. All of them show dissimilar behaviors with temperature, pointing out to their distinct nature. A temperature-dependent central mode at THz frequencies and a relaxation above 10 GHz are accompanied by the slowing down of a relaxation in the MHz range. This response reveals the complex mechanism of the phase transition and supports the coexistence of displacive and order-disorder scenarios. Relaxor and ferroelectric compositions surprisingly reveal similar qualitative behavior within the frequency window used. However, relaxor crystals display relaxations at higher frequency because of the smaller extent of the polar fluctuations and ferroelectric regions, which coexist in almost all the compositions. The presence of two different ferroelectric subsystems in the structure agrees with the existence of several polarization mechanisms involved in the complex dielectric and ferroelectric response.

Structure, antiferro/ferro-electric transformation and relaxor behaviour in (1-x)Pb(Yb1/2Nb1/2)O3-xPb(Mg1/2W1/2)O3 ceramics

The superlattice structure and dielectric relaxor behaviour were simultaneously observed in (1-x)Pb(Yb1/2Nb1/2)O3-xPb(Mg1/2W1/2)O3 ((1-x)PYN-xPMW) ceramics composed by highly ordered end members. Orthorhombic perovskite structure was determined by X-ray diffraction for the compositions of x = 0·0–0·2 and 0·8–1·0 with two sets of superlattice. For intermediate compositions, the superlattice peaks were still preserved with weakening in intensity. Strong dielectric relaxor behaviour seemed to be independent with the superlattice and well fitted by Vogel–Fulcher equation for x = 0·3–0·7. It indicated that the polar microregions in (1-x)PYN-xPMW undergo the dipole glass-like and freezing state analogous to the prototypical relaxor Pb(Mg1/3Nb2/3)O3. Slim ferroelectric hysteresis loops, seemingly made up with ferroelectric and antiferroelectric together, were obtained for the relaxor compositions using huge external field. The antiferroelectric compositions related to superlattice were determined through double ferroelectric polarisation loops. A schematic diagram was sketched to describe the structure transform and generation of relaxor behaviour.

Electric field-induced changes of domain structure and properties in La-doped PZT—From ferroelectrics towards relaxors

Electromechanical properties and crystal and domain structures of piezoelectric ceramics from the Pb1−xLax(Zr0.65Ti0.35)1−x/4O3 (x/65/35 PLZT) solid solution system were systematically analysed by electrical measurements, X-ray diffraction and scanning electron microscopy. The compositionally-driven phase transition from a rhombohedral ferroelectric into a pseudocubic relaxor state is accompanied by a decrease in domain size and changes in domain morphology. SEM analyses of the ex-situ poled samples showed that only in the ferroelectric compositions domain configuration changed, while in the relaxor compositions no domain changes were detected. In order to evaluate the extrinsic contribution to enhanced piezoelectric properties in relaxors, in-situ environmental scanning electron microscopy analyses with applied external electric field were performed. Extrinsic effects as a result of poling were predominant in the ferroelectrics, whereas the intrinsic effect prevailed in the relaxors. Finally, a model of electric field-induced displacements as a result of decreasing domain size for the ferroelectric-to-relaxor PLZT materials was proposed.

Investigation of the Physical Properties of PLZT Ferroelectric Ceramics – Effect of the Lanthanum Content

In this work, the structural, ferroelectric and dielectric properties, including radio-frequencies and microwave region, has been investigated in Pb1 − xLax(ZryTi1 − y)1 − (x/4)O3 (PLZT) ferroelectric ceramics, where x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12 and y = 0.70. Ceramic samples were obtained from the solid-state reaction sintering method, and the dielectric measurements were performed in a wide frequency and temperature region, below and above the paraelectric-ferroelectric (PE-FE) phase transition temperature. The structural properties, investigated at room temperature, from the x-ray diffraction (XRD) technique, revealed the evolution from the rhombohedral (R3m symmetry) to orthorhombic (Pmmm symmetry) phases, with the increase of the lanthanum concentration. The ferroelectric as well as the low frequency dielectric properties revealed a change in the PE-FE phase transition characteristics from a normal to a relaxor behavior, with the increase of the lanthanum content. On the other hand, the high-frequency (microwave) dielectric properties studied at room temperature, showed a strong dielectric dispersion on both normal (x≤0.06) and relaxor (x>0.06) compositions, which indeed revealed to be also strongly dependent on the lanthanum concentration.

Measurement of thermal strain and total polarization estimation of lead zirconate titanate–lead zinc niobate ceramics

Thermal expansion properties have been measured for the ceramic lead zirconate titanate–lead zinc niobate [(1 − x)PZT–(x)PZN] in the temperature range of −100 to +450 °C. For all ceramics examined, the deviations from the straight line below Burns temperature were observed. The dynamic polarization fluctuations in their relaxor compositions are believed to play a role in this deviation. Burns temperature was determined and the local polarization (P d) was calculated from the thermal expansion data. Various aspects of understanding the polarization behavior and other effects in this ferroelectric system were examined and discussed.

Electro-caloric effect in relaxor and ferroelectric compositions of Pb(Mg(1−x)/3Nb2(1−x)/3Zrx)O3 ceramics

Solid solution of relaxor PMN and antiferroelectric PZ, [Pb(Mg(1−x)/3Nb2(1−x)/3Zrx)O3], behaves like ferroelectric with increasing PZ content following a wide composition range of diminishing relaxor properties. Electro-caloric measurements on three relaxor and one ferroelectric composition of this solid solution have been carried out by indirect method. All the compositions give a maximum temperature change of ∼0.33K on application of 1kV/mm electric field. This value is higher than the PLZT or PMN–PT based relaxors. A shift of ∼35°C in the temperature of electro-caloric maximum was observed with application of electric field, for relaxor compositions, attributed to the field induced effect on the transition temperature. Similar shift for ferroelectric composition is significantly lower (∼8°C).

Structural, dielectric, and piezoelectric properties of BaTiO3-Bi(Ni1/2Ti1/2)O3 ceramics

Undoped and Mn-doped (1−x)BaTiO3–xBi(Ni1/2Ti1/2)O3 (x = 0.03–0.7) ceramics were synthesized by a conventional solid state route. X-ray diffraction patterns revealed that the crystal structure was a tetragonal perovskite at x = 0.03, a pseudo-cubic perovskite at x = 0.1 and 0.3, and mixed phases at x = 0.5–0.7. The dielectric and piezoelectric responses were ferroelectric at x = 0.03 and relaxor-like at x = 0.1–0.7. The polarization–electric field and strain–electric field responses were suppressed at the relaxor compositions, and the large-field piezoelectric constant was 25–40 pm/V at x = 0.3–0.7. As x increased, the temperature of the maximum dielectric constant decreased compared to the Curie temperature of BaTiO3 at x ≤ 0.1, and then it increased and reached 325°C at x = 0.7. At x = 0.3–0.7, the dielectric constant was less temperature dependent. These results suggest that the samples may be suitable for high temperature capacitor application.

Lead‐Free Relaxor Ferroelectrics

Feature size is a natural determinant of material properties. Its design offers the technological perspectives for material improvement. Grain size, crystallite size, domain width, and structural defects of different nature constitute the classical design elements. Common ferroelectric ceramics contain micrometer grain sizes and submicrometer domain widths. Domain wall mobility is a major contribution to their macroscopic material properties providing approximately half of the macroscopic output in optimized materials. The extension into the dynamic nanoworld is provided by relaxor ferroelectrics. Ionic and nanoscale field disorders form the base to a state with natural nanometer‐size polar structures even in bulk materials. These polar structures are highly mobile and can dynamically change over several orders of magnitude in time and space being extremely sensitive to external stimuli. This yields among the largest dielectric and piezoelectric constants known. In this feature article, we want to outline how lead‐free relaxors will offer a route to an environmentally safer option in this outstanding material class. Properties of uniaxial, planar, and volumetric relaxor compositions will be discussed. They provide a broader and more interesting scope of physical properties and features than the classical lead‐containing relaxor compositions.

Monte Carlo simulations for describing the ferroelectric–relaxor crossover inBaTiO3-based solid solutions

The properties induced by the M4 + addition (M = Zr,Sn, Hf) in BaMxTi1 − xO3 solid solutions have been described on the basis of a 2D Ising-like network and Monte Carlo calculations,in which BaMO3 randomly distributed unit cells were considered as being non-ferroelectric.The polarization versus temperature dependences when increasing theM4 + concentration(x) showed a continuous reduction of the remanent polarization and of the criticaltemperature corresponding to the ferroelectric–paraelectric transition and a modificationfrom a first-order to a second-order phase transition with a broad temperature range forwhich the transition takes place, as commonly reported for relaxors. The model alsodescribes the system’s tendency to reduce the polar clusters’ average size whileincreasing their stability in time at higher temperatures above the Curie range,when a ferroelectric–relaxor crossover is induced by increasing the substitution (x). The equilibrium micropolar states during the polarization reversal process while describing theP(E) loops were comparatively monitored for the ferroelectric (x = 0) andrelaxor (x = 0.3) states. Polarization reversal in relaxor compositions proceeds by the growth of several nucleateddomains (the ‘labyrinthine domain pattern’) instead of the large scale domain formationtypical for the ferroelectric state. The spatial and temporal evolution of the polar clusters inBaMxTi1 − xO3 solid solutionsat various x has also been described by the correlation length and correlation time. As expected for theferroelectric–relaxor crossover characterized by a progressive increasing degree of disorder,local fluctuations cause a reducing correlation time when the substitution degree increases,at a given temperature. The correlation time around the Curie temperature increases,reflecting the increasing stability in time of some polar nanoregions in relaxors incomparison with ferroelectrics, which was experimentally proved in various types ofrelaxors.

Estimation of Total Polarization and Thermal Expansion Behavior in PZT-PCN Ceramics

Thermal expansion properties of (1−x)PZT–(x)PCN ceramics were determined in the temperature range of approximately −100 to +450°C by dilatometer thermal expansion measurement. The observed deviation from the straight line below Burns temperature for all the compositions was interpreted as due to the dynamic polarization fluctuations in their relaxor compositions. Burns temperature was determined and found to increase with increasing PZT concentration. The local polarization was also calculated from the thermal expansion data. Various aspects of understanding the polarization behavior and other effects in this mixed normal-relaxor ferroelectric system were also examined and discussed.

Evaluation of Experimental Resume of BaZrxTi1-xO3 with Perspective to Ferroelectric Relaxor Family: An Overview†

In this paper we report the mechanism and nature of relaxor ferroelectric behavior in the environmental friendly lead free Barium Zirconate Titanate (BZT) system. A revised complete (Structure:Property) phase diagram of Ba(ZrxTi1-x)O3, with compositions 0.00≤ × ≤1.00 has been developed based on their electrical properties. Two different kinds of relaxor behaviors have been observed in the BZT system; one is dominated by polar Ti-rich regions and another by non-polar Zr-rich regions. All the BZT relaxor compositions are characterized by dielectric properties with and without bias, pyroelectric and thermal expansion measurements in the wide range of temperatures. The structure of the BZT compositions has been evaluated by XRD, Neutron diffraction study. Further the local structure of the BZT compositions has been probed by micro-Raman spectra. Although the global structure of BZT relaxors is cubic as observed in Neutron diffraction studies, the local symmetry is non-cubic as evident in the micro-Raman spectra of BZT relaxors as well as in their thermal strain measurement, dielectric and pyroelectric behavior.

Evolution from Ferroelectric to Relaxor Behavior in the (1 − x)BaTiO3 − xLa(Mg1/2Ti1/2)O3 System

Ceramics of (1 − x)BaTiO3−xLa(Mg1/2Ti1/2)O3 series (x = 0, 0.025, 0.05, 0.075 and 0.1) were dielectrically investigated. Based on the dielectric and X-ray diffraction data, phase diagram of the system for the studied composition range has been determined. Apparent relaxor behavior was revealed to set in when the BaTiO3-type sequence of three phase transitions is reduced to only diffuse transition. No clear boundary was found between ferroelectric and relaxor compositions of the system. It was observed the continuous crossover from ferroelectric to relaxor behavior.

Microwave dielectric relaxation process in doped-incipient ferroelectrics

The electrical permittivity properties in the microwave frequency range were investigated in incipient and relaxor compositions of Sr 1− x Ca x TiO 3 ceramics from 60 to 440 K. The results revealed that the origin of microwave dielectric relaxation process lies in the appearance of nanometric polar regions rather than any other ferroelectric or piezoelectric mechanism. The experimental data also showed that the relaxation frequency is reasonably independent of the correlation length. The occurrence of more stable polar phase into the grain bulk induced by dipole moment related to the grain boundaries was also verified.

NaNbO3-Based Relaxor

Binary NaNbO3-ABO3 perovskite solid solutions belonging to the group II according to N.N. Krainik classification (Izv. Akad. Nauk SSSR, Ser. Phys. 28, 643 (1964)) exhibit a relaxor-type behavior when the second component concentration exceeds a threshold value x0, corresponding to the abrupt decrease of the dielectric permittivity ϵ maximum temperature Tm. The Tm values of all the known binary NaNbO3-ABO3 relaxor compositions are well below the room temperature and the maximal ϵ values ϵm are much lower than in the case of Pb-containing relaxors. However both Tm and ϵm values may be increased substantially by Li or K-doping leading to the formation of ternary NaNbO3-ABO3-LiNbO3 (KNbO3) solid solutions.

Lead-free relaxors with“TTB” structure containing either lanthanum or bismuth

TTB-type lead-free relaxor compositions containing either lanthanum or bismuth were studied. Their temperature and frequency dielectric properties were investigated on ceramics. The relaxor characteristics of similar compositions containing either lanthanum or bismuth were compared. The value of Tm, the temperature of the maximum of e′r, was systematically higher for bismuth samples. The values of ΔTm, the variation of Tm from 102 to 105 Hz, were very high. With a value of Tm near to room temperature, BaBiNb5O15 seems to be a good candidate for environment-friendly applications. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Canonical-glass-like behavior of the polycrystalline relaxor ferroelectric (1–x)PbMg1/3Nb2/3O3–xPbZrO3: Heat-capacity study

A solid solution of lead magnesium niobate (PMN), a relaxor ferroelectric, with lead zirconate (PZ), an antiferroelectric, gives rise to a system that behaves like a relaxor ferroelectric for lower concentrations of PZ, and like a normal ferroelectric above 50% substitution by PZ. This paper reports the heat-capacity behavior of (1 –x)PMN–xPZ for the composition rangex= 0.30 to 0.95 and temperature range 300–600 K. It was observed that, although the atomic structure of the material is basically crystalline throughout, with sharp x-ray diffraction peaks, the crossover from normal–ferroelectric behavior to relaxor–ferroelectric behavior (on decreasingx) is accompanied by a matching crossover from crystalline behavior to glassy behavior, as exhibited in the heat-capacity plots. In other words, the heat-capacity curves for the relaxor compositions bear resemblance to those observed for canonical or conventional glasses, with the glass-transition temperature and the continuous step in specific heat changing gradually as a function of the composition parameterx. However, not all properties match those for canonical glasses. For example, soaking for 24 h at a temperature or 10 to 20 K below the mean glass-transition temperature does not raise the specific heat to a value nearly equal to the value in the unfrozen state. Similarly, the glass-transition temperature (for 0.7PMN–0.3PZ) increases, though only marginally (from 337 K to 343 K), when the rate of heating across the transition is increased by a factor of 50 (from 0.1 K per minute to 5 K per min.). Further, the temperature interval ΔT over which most of the glass transition occurs in the relaxor ferroelectric is typically as large as 30–40 K, compared to only about 10 K for canonical glasses.

TKWB-Type Lead-Free Oxyfluoride Relaxors Derived from Ba2NaNb5O15

Three solid solutions were prepared from Ba 2 NaNb 5 O 15 by coupled cationic and/or anionic substitutions: Ba 2-x Na 1+x (Nb 5-x W x )O 15 . Ba 2-x Na 1+x Nb 5 O 15-x F x and Ba 2 NaNb 5-x Ti x O 15-x F x . They crystal-lize with a TKWB-type structure. In the case of oxyfluoride compositions, large frequency range dielectric studies performed on ceramics demonstrated a relaxor behavior. The greater the substitution rate, the higher the relaxor corresponding characteristics. Such a behavior is in agreement with the cationic disorder of Ba 2+ and Na + in the same crystallographic site of BaNa 2 Nb 5 O 14 F. In addition, the following transition sequence was obtained: relaxor → ferroelectric → paraelectric. Such ceramics constitute a new family of lead-free relaxor compositions with TKWB structure and can be used in environmental-friendly applications.