Relaxor Crossover Research Articles

Ergodic polar cluster state and its dynamics in K and Nb modified BaTiO3

Ferroelectric to relaxor crossover of (KxBa1-x)(NbxTi1-x)O3 [KBNTx]; (x = 0, 0.05, 0.075 and 0.150) system has been investigated by exploring its average and local structure using X-ray diffraction, Raman scattering and dielectric spectroscopy. X-ray diffraction confirmed all compositions' overall cubic (Pm-3m) structure. Dielectric spectroscopy clearly showed ferroelectric to relaxor crossover at x = 0.150. In the Raman spectra of doped compounds, three new modes of chemical origin that are absent in BaTiO3 are observed at frequencies ∼120 cm−1, 830 cm−1 and 850 cm−1 at room temperature. The temperature-dependent Raman scattering revealed the existence of ergodic polar regions by the presence of first-order ferroelectric mode at 302 cm−1 [B1/E(TO3)/E(LO2)], along with two static disorder-related modes 220 and 550 cm−1 for T > Tc in the paraelectric phase. Moreover, Raman studies also elucidate that the decreased size of ergodic polar regions is responsible for relaxor crossover at x = 0.150 composition with the increased broadening of 302 cm−1 modes with an increase of K and Nb concentration. Further, the polar dynamic investigations indicated that the interactions among polar nano regions slow down nano-polar dynamics without freezing or glass transition. Identifying polar regions and their dynamics in the present work will significantly impact the understanding of the tunability of K and Nb-modified BaTiO3 lead-free ferroelectrics.

Is electrostrain >1% in oxygen deficient Na0.5Bi0.5TiO3 a composition effect?

Abstract For over two decades Na0.5Bi0.5TiO3 (NBT) -based lead-free piezoelectrics have attracted attention due to its ability to exhibit large electric-field driven strain. Compared to the popular Pb(Zr, Ti)O3 (PZT)-based piezoelectrics, which exhibit electrostrain of about 0.3%, the derivatives of NBT-based lead-free piezoelectrics at the ergodic—non ergodic relaxor crossover exhibit larger electric-field driven strain ∼0.45%. In recent years, there has been a concerted effort to increase the maximum electrostrain in lead-free piezoceramics. Recent reports suggest that oxygen deficient NBT- based piezoceramics can exhibit electrostrain ∼1%. In this paper we explore this phenomenon and show that the ultra high electric field driven strain measured is primarily a consequence of reducing the thickness of the disc dimension below 500 microns and not an exclusive effect of the composition.

Intermediate ferroelectric phase driven ferroelectric-relaxor crossover and superior storage properties in phase boundary engineered BCZT ceramics

Compositional tuning in materials at the morphotropic phase boundary has been a novel strategy to realize unprecedented and exotic physical properties. This work reports the structural, dielectric, electrical, and energy storage properties in lead-free BCZT (Ba0.85Ca0.15Zr0.1Ti0.9O3) at the morphotropic phase boundary (MPB) through compositional engineering at Ba-site. The polycrystalline samples of Ba0.85(1-x)(La1/2Na1/2)0.85xCa0.15Zr0.1Ti0.9O3 (x = 0.0, 0.05, 0.075, 0.1) are synthesized by mechanical alloying followed by heating the samples at elevated temperatures. Rietveld refinement of powder X-ray diffraction patterns unveils coexisting ferroelectric P4mm (tetragonal) and ferroelectric R3m (Rhombohedral) symmetries, for samples x = 0.0–0.075. Intriguingly, the sample with x = 0.10 supports the inclusion of an intermediate ferroelectric phase with orthorhombic (Amm2) symmetry along with P4mm and R3m symmetries. Dielectric studies reveal a structurally coherent normal ferroelectric-ergodic relaxor crossover with Vogel-Fulcher type freezing of polar-nano-regions. Furthermore, the La/Na co-doping substantially enhances the recoverable energy density (Wrec); from 357 mJ/cm3 to 664 mJ/cm3, reduces the loss energy density (WL); from 101 mJ/cm3 to 42 mJ/cm3 and increases the storage efficiency (η); from 77.9% to 94%. The doping-induced enhanced dielectric and storage properties are elucidated by impedance spectroscopy and density functional theory (DFT)-based calculations.

Enhanced dielectric, thermal stability, and energy storage properties in compositionally engineered lead-free ceramics at morphotropic phase boundary

Structural inhomogeneity at morphotropic phase boundary (MPB) offers a novel paradigm to explore and modulate the physical properties of dielectric materials to design next-generation multifunctional devices. In this work, two lead free materials at MPB; Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) and (Bi0.5Na0.5)TiO3-0.06BaTiO3 (BNTBT), are combined together to synthesize polycrystalline composite samples of (1-x) BCZT-xBNTBT with x = 0.0, 0.25, 0.50, 0.75, and 1.0. Structural investigations using XRD show the coexistence of double phases for pristine BCZT (tetragonal (P4mm) + rhombohedral (R3m)), and for pristine BNTBT (tetragonal (P4bm) + rhombohedral (R3c)). However, all the doped samples with x = 0.25, 0.5, and 0.75 display a coexistence of triple phases with P4mm, P4bm, and R3c symmetries. Detailed dielectric study reveals a normal ferroelectric to macroscopic ergodic relaxor crossover for samples with x = 0.25 and 0.75. Intriguingly, sample x = 0.25 displays a coexistence of high dielectric constant (4050), ultralow dielectric loss (≤0.02), high temperature thermal stability of permittivity (variation ≤ ±15%) in a temperature range 135 °C–450 °C, large recoverable energy density (Wrec = 423 mJ/cm3) with ultrahigh energy storage efficiency (η = 95.4%) at low applied electric field - 23 kV/cm. Nevertheless, at similar applied field strength, the obtained values of Wrec and η exceed most of the selected lead-free energy storage materials. This work may pave a new path to design superior high-temperature dielectrics, through intermixing of MPBs, for energy storage applications.

Ferroelectric to relaxor crossover in Li solid solutions derived from Ba2Nd□2FeNb4O15

Three solid solutions of Tetragonal Tungsten Bronze structure containing Li were prepared by solid state route starting from the parent compound Ba2NdFeNb4O15. These solid solutions involve Li insertion compensated by cationic removal. All cationic sites were involved to investigate their influence on the dielectric transitions observed in Ba2NdFeNb4O15, i.e. from relaxor (R) to ferroelectric (FE) and finally to paraelectric (PE). All solid solutions display the same pattern, which is an evolution from a relaxor to ferroelectric crossover, leading to a single transition (relaxor to paraelectric). This evolution is accompanied by a sudden increase of the ordering temperature (Tm). A focus on structure refinements shows the slight differences induced by the insertion of Li and points towards the role of anionic framework as responsible for the dielectric properties of these materials. This study completes the work performed on other cationic substitutions performed in the title material, and represents a new example of Li substituted TTB materials.

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.

Ferroelectric‒to‒relaxor crossover in KNN‒based lead‒free piezoceramics

This study investigated the phase transition behavior and electrical properties of (K0.5Na0.5)(Nb1-xZrx)O3 (KNN‒100xZ) and (K0.5Na0.5)NbO3–yBaZrO3 (KNN–100yBZ) lead–free piezoelectric ceramics. The phase transitions in crystal structures were compared in KNN ceramics between single Zr4+ doping and Ba2+Zr4+ co−doping. Piezoelectric properties such as the piezoelectric constant (d33) and electromechanical coupling factor (kp) are optimized for KNN‒6BZ ceramics and were clarified via the polymorphic phase transition from the orthorhombic to pseudocubic phase. The fitted degree of diffuseness (γ) for a phase transition from the modified Curie–Weiss law indicated that KNN ceramics as ferroelectrics are gradually transformed through BaZrO3 modification. Accordingly, the enhanced strain properties at y = 0.08 consist of coexisting ferroelectric domains and polar nanoregions that are supported by ferroelectric–to–relaxor crossover in KNN‒100BZ ceramics.

Ferroelectric to relaxor crossover in antimony doped (Pb0.80Ba0.20)(Zr0.70Ti0.30)O3 ceramics

The effect of the antimony dopant on the crystallographic structure, phase transition, dielectric response, and relaxor behaviour of (Pb0.80Ba0.20)(Zr0.70Ti0.30)O3 ceramics have been studied. Ceramic samples, with Sb concentrations varying from 0.5 to 2mol% Sb2O5, were prepared by a conventional mixed oxide method. The crystal structure of the examined ceramics was determined by X-ray diffraction at room temperature. This allowed us to define the unit cell parameters, as well as atomic positions. Moreover, dielectric relaxation typical for ferroelectric relaxors was observed. All parameters describing the relaxor behaviour determined from the Vogel–Fulcher relationship depended on the concentration of the Sb dopant. A strong influence of antimony on the grain structure was also confirmed.

Multiscale study of ferroelectric–relaxor crossover in BaSnxTi1−xO3 ceramics

Abstract A systematic study of BaSn x Ti 1− x O 3 solid solutions ( x = 0–0.20) by a combined field-induced dielectric and ferroelectric analysis with Raman and PFM investigations was realized, in order to obtain new insights concerning the composition-induced modification of the structural phase transitions and ferroelectric–relaxor crossover induced by the increase of Sn addition. The ceramics prepared via solid state reaction and sintering at 1400 °C/4 h showed average tetragonal symmetry for x ≤ 0.15 and cubic for x = 0.20. However, the dielectric and Raman analysis demonstrated that x = 0.05 and x = 0.15 are characterized by a coexistence of phases, which enhances their macroscopic properties (polarization for x = 0.05 and permittivity for x = 0.15). The domain structure shows a gradual modification when increasing Sn addition. No detectable domain structure has been found for x ≥ 0.15. All the compositions show local d 33 ( V ) hysteresis loops at room temperature.

Raman and dielectric response of BaTi1-x(Mg1/3Nb2/3)xO3 solid solution

Structural evolution and dielectric analysis have been performed for BaTi 1-x( Mg 1/3 Nb 2/3)x O 3 solid solutions with x ≤ 0.07, together with the analysis of Raman spectroscopy. X-Ray diffraction and Raman results show a structural evolution from a tetragonal phase to a cubic one with increasing x. Dielectric analysis reveals a low critical concentration corresponding to ferroelectric–relaxor crossover (xc = 0.05). Activation energy with dozens meV is obtained using the Vogel–Fulcher relationship, which is attributed to thermally activated off-center ion hopping.

Investigation of the ferroelectric–relaxor crossover in Ce-doped BaTiO3 ceramics by impedance spectroscopy and Raman study

BaCe x Ti1− x O3 (x = 0.06, 0.10, and 0.20) solid solutions were prepared via conventional the solid-state reaction and sintered at 1500°C for 4 h, resulting in dense single phase ceramics with homogeneous microstructures. The electric field dependence of permittivity of the BaCe x Ti1− x O3 ceramics was investigated in detail, together with the ferroelectric–paraelectric phase transition features. A transformation from normal to relaxor ferroelectrics was observed by increasing the Ce concentration. For low-Ce content, a substitution of Ce on both A and B site positions was proposed from the dielectric study and confirmed by Raman analysis.

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.

Ferroelectric–relaxor crossover characteristics in Ba(Zr xTi 1− x)O 3 ceramics investigated by AFM-piezoresponse study

Ba(Zr x Ti 1− x )O 3 ceramics with x = 0.10 and 0.18 prepared via solid state, with high-density, homogeneous microstructures and similar grain size were investigated. The dielectric data showed that the relaxor properties are induced by increasing the Zr vs. Ti fraction x, both compositions showing a combined relaxor–ferroelectric character. The AFM-piezoresponse experiments revealed a few interesting characteristics, as follows: (1) none of the samples could be totally poled or switched, like the normal ferroelectrics; (2) the samples locally present different types of responses (ferroelectric with a strong piezoresponse, field-induced ferroelectric, polar but non-switchable and non-polar regions); (3) both the regions with a natural strong piezoresponse and the ones obtained after poling are larger in size and more stable in time for the sample with x = 0.10 than for x = 0.18; (4) the sample having x = 0.18 has a smaller piezoresponse than the one with x = 0.10. The observed local features are confirming the ferroelectric–relaxor crossover with increasing x, as observed by the analysis of the dielectric data.

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

The (1−x)BaTiO3–xBaSnO3 (0⩽x⩽0.30) perovskite solid solution ceramics were prepared by solid state reaction and studied by dielectric spectroscopy. The complex dielectric permittivity was measured as a function of frequency (0.1Hz–100kHz) in the temperature (T) range of 123–573K. The transition from the high-temperature paraelectric state where the dielectric constant obeys the Curie-Weiss law to the ergodic cluster state is found to occur at the same temperature of 485K in all the compositions of x⩾0.04 and at lower temperatures in those with a smaller x. For 0⩽x⩽xc=0.19, the temperature of the dielectric peak Tm, corresponding to the diffuse transition from the ergodic polar cluster state to the ferroelectric state, decreases with increasing x and does not depend on frequency. The diffuseness of the peak gradually increases. For x>xc, the permittivity exhibits relaxor behavior with the frequency-dependent Tm satisfying the Vogel-Fulcher law. The temperature variation of the permittivity on the high-temperature slope of the peak (T>Tm) is characterized by the characteristic Lorenz-type quadratic law for relaxors, with the diffuseness increasing with the increase of x. The mechanisms of the dielectric response in different parts of the phase diagram are discussed. In particular, the crossover from diffuse ferroelectric phase transition to relaxor ferroelectric behavior is attributed to the appearance at x>xc of the additional dielectric contribution arising from the flipping of the local polarization of the polar clusters. The temperature-composition phase diagram of the Ba(Ti1−xSnx)O3 system has been established, which delimits the paraelectric, ergodic polar cluster, nonergodic ferroelectric, and relaxor phases (states) and indicates the crossover from ferroelectric to relaxor behavior at x=xc.

Anion-Deficient Perovskite Pb(Mg0.5Nb0.5)O2.75 Ceramics Obtained under High Pressure

Single phase ceramics with the composition Pb(Mg0.5Nb0.5)O2.75 (PMN-V) were prepared under high pressure and temperature conditions. Cubic perovskite phase of PMN-V with a lattice parameter a = 4.0495 ± 0.0003 Å was revealed to be stable at normal pressure up to 1120 K. Temperature dependence of dielectric response of the high-pressure sintered PMN-V ceramics showed two particular regions: a diffuse ferroelectric transition with the frequency independent maximum and a typical relaxor crossover at lower temperature. Effect of high-pressure and stoichiometry (oxygen vacancies) on the B-site cation ordering and dielectric behaviour of PMN is discussed.