Typical Relaxor Ferroelectrics Research Articles

Slow and non-equilibrium dynamics due to electronic ferroelectricity in a strongly-correlated molecular conductor

Ferroelectricity, where electronic degrees of freedom determine the polar order—thereby enabling fast switching and phase control—is an important research field in current condensed-matter physics. Using a combination of resistance noise and dielectric spectroscopy we investigate the nature of relaxor-type electronic ferroelectricity in the organic conductor κ-(BETS)2Mn[N(CN)2]3, a system that represents a wider class of materials of correlated electron systems for which functionalities for organic spintronics recently have been discussed. The two complementary spectroscopies reveal a distinct low-frequency dynamics on different length scales, namely (i) an intrinsic relaxation that is typical for relaxor ferroelectrics which classifies the system as a possible new multiferroic, and (ii) two-level processes which we identify as fluctuating polar nanoregions (PNR), i.e., clusters of quantum electric dipoles that fluctuate collectively. The PNR preform above the metal insulator (MI) transition. Upon cooling through TMI, a drastic increase of the low-frequency 1/f-type fluctuations and slowing down of the charge carrier dynamics is accompanied by the onset of strong non-equilibrium dynamics indicating a glassy transition of interacting dipolar clusters. The freezing of PNR and non-equilibrium dynamics is suggested to be a common feature of organic relaxor-type electronic ferroelectrics.

Synthesis of single phase Ti4+ substituted Trirutile CoNb2O6 Ceramic: evolution of Relaxor type ferroelectricity and high k dielectricity

Synthesis of single phase Ti4+ substituted Trirutile CoNb2O6 Ceramic: evolution of Relaxor type ferroelectricity and high k dielectricity

On the Enhancement of Energy Storage Performance in Modified Relaxor Ferroelectric Ceramics for Pulsed Power Applications

Relaxor-type ferroelectrics show important potential in energy storage fields due to their significantly enhanced energy performance and good temperature stability compared to normal ferroelectrics. Here, a novel, high-performance ternary composition, (0.4−x)BiFeO3-xBi(Mg1/2Ti1/2)O3–0.6BaTiO3 (x = 0.2, 0.25, 0.3, 0.35, 0.4), was designed by compositional modulation, which displays typical relaxor characteristics. The optimum energy storage properties can be attained at x = 0.35, accompanied by energy efficiency of 84.87%, a promising energy storage density of 2.3 J/cm3 and good temperature stability of less than 10% over 20–160 °C. Moreover, the samples provide stable cycling fatigue after 105 cycles and a fast discharge time of t0.9 < 0.1 μs, indicative of promising applications in energy units.

Synthesis, structural characterization and functional properties of Sr0.5Ba0.5Nb2−xFexO6 ceramic powders

Sr0.5Ba0.5Nb2-xFexO6 (SBNF) ceramic powders for x=0.00, x=0.02 and x=0.03 were synthesized using coprecipitation method. The structure of the SBNF single phase with x=0.02 was identified by X-ray diffraction and Rietveld refinement; the morphology and size of the particles were observed by TEM and SEM-EDS microscopy. Electrical characterization showed that Fe doping did not cancel the typical ferroelectric relaxor behavior and magnetic characterization showed a weak ferromagnetic response, which suggest that the samples obtained can be considered as multiferroic.

Relaxor behavior and superior ferroelectricity of Y2O3-doped (Ba0.98Ca0.02) (Ti0.94Sn0.04Zr0.02)O3 lead-free ceramics

To upgrade the electric properties of lead-free piezoceramics, (1–x)(Ba0.98Ca0.02Ti0.94Sn0.04Zr0.02)O3-xY2O3 (abbreviated as (1–x)BCTSZ-xY, x = 0 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol% and 0.1 mol%) ceramics were successfully synthesized by traditional solid-state sintering method. The phase structure and microstructure of ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and piezoresponse force microscopyeramics (PFM). The electric properties of ceramics were researched through piezoelectric, dielectric and ferroelectric test instruments. The results show that all samples have pure perovskite structure and favorable electric properties. The optimal electric properties which especially include superior ferroelectric properties are gained when Y2O3 content is 0.06 mol% (d33 = 419 pC/N, kp = 52%, Tc = 89.5 °C, εr = 26900, tanδ = 2.86%, Pr = 14.41 μC/cm2, Ec = 1.8 kV/cm). Moreover, the temperature-dependent dielectricity of samples shows apparent relaxor behavior under different frequencies. The Curie–Weiss law further proves that all samples are typical relaxor ferroelectrics, and the relaxor degree of samples decreases with increase of Y2O3 content. In conclusion, Y2O3 plays a significant role in enhancing electric properties of BCTSZ ceramics.

Possibility of relaxor-type ferroelectricity in delafossite CuCrO2 near room temperature

Ceramic sample of CuCrO2 was synthesized via a solid-state reaction method. XANES, dielectric, ferroelectric, pyroelectric, synchrotron x-ray diffraction (SXRD), transmission electron microscope (TEM) and Raman measurements were performed on the prepared sample. Ferroelectric hysteresis loop, PUND, and pyroelectric current measurements indicate the presence of ferroelectricity in the prepared sample. The appearance of a broad maximum in dielectric permittivity and its frequency dispersion indicates the possibility of relaxor-type ferroelectricity in the system. Furthermore, TEM measurements revealed the presence of nano regions that are speculated to be polar and hence are giving rise to relaxor-type ferroelectricity. Careful analysis of XRD data indicates that the distorted CrO6 octahedra is giving rise to strain in the sample. This strain might be responsible for the observed nano regions, which might be polar, in the otherwise non-polar matrix. It is proposed that these polar regions are responsible for the presence of relaxor-type ferroelectricity in the sample.

Perovskite Bi0.5Na0.5TiO3-based materials for dielectric capacitors with ultrahigh thermal stability

There has been recently a great progress in the development of dielectric capacitors for high temperature electronic applications. The design of lead-free ceramics with high dielectric permittivity, low dielectric loss and a limited variation of these parameters over a wide temperature range is still a big challenge. In this work, lead-free Bi0.35Na0.65–0.5xRb0.5xTi0.7Nb0.3O3 (x = 0–0.05) bulk ceramics were prepared using the solid-state reaction method. Upon Rb substitution, the variation of the dielectric permittivity was reduced substantially, in particular, at high temperature (over 200 °C). In addition, a low temperature coefficient of capacitance (TCC ≤ 10%) together with an ultra-low dielectric loss (tanδ ≤ 0.05) were achieved for the Bi0.35Na0.63Rb0.02Ti0.7Nb0.3O3 sample in the temperature range from −43 °C to 292 °C. The new relaxor-type ferroelectrics also possess the outstanding stability of the dielectric properties under high DC bias voltage, which makes them promising materials for high-performance capacitors of the next generation.

Superior Electrostrictive Effect in Relaxor Potassium Sodium Niobate Based Ferroelectrics.

Electromechanical actuators with toxic lead-based electrostrictive materials dominate the market of high-precision electronics devices, so one of urgent aims becomes how to explore the new generation of ecofriendly electrostrictive materials with superior electrostriction behaviors. Herein, a strategy of modifying the active space for the B-site in lead-free relaxor ferroelectrics arouses the potential capacity of electrostriction, including K0.5Na0.5NbO3 (KNN). Through co-doping of Bi3+ and Ni2+, typical relaxor ferroelectrics (1 - x)K0.5Na0.5NbO3-xBiNi2/3Nb1/3O3 (KNN-xBNN, 0.03 ≤ x ≤ 0.07) are constructed because of the incorporation of dopants ions on the A- or B-site promotes structural disorder. Importantly, a limited active space for the B-site is obtained owing to the contracted oxygen-octahedron with smaller A-site dopants induced by lattice distortion. Benefiting from the design strategy, a remarkable enhancement of electrostrictive coefficient Q33 of ∼0.0456 m4/C2 is achieved, which is higher than those of KNN-based materials and also twice as large as those of lead based materials. The Q33 also exhibits a relatively good electric field and is temperature-independent. A giant Q33 of 0.0512 m4/C2 is gained at a high frequency of 100 Hz, meeting the requirement of some commercial actuators for fuel injectors. Such a strategy may help us design high-performance electrostrictive materials.

Tunable surface acoustic waves on strain-engineered relaxor K0.7Na0.3NbO3 thin films

In this work, we demonstrate the electronic tunability of surface acoustic waves (SAWs) in epitaxially strained relaxor-type ferroelectric thin films. Epitaxial K0.7Na0.3NbO3 thin films of typically 30 nm in thickness are grown via pulsed laser deposition on (110)-oriented TbScO3. A partial plastic lattice relaxation of the epitaxial strain in these samples leads to a relaxor-type ferroelectricity of these films, which strongly affects the SAW properties. Without electronic bias, only tiny SAW signals of ∼0.2 dB can be detected at room temperature, which can be boosted up to ∼4 dB by a static voltage bias added to the high frequency driving current of the SAW transducers. Upon field cooling below the freezing temperature of polar nanoregions (PNRs), this strong SAW signal can be preserved and is even enhanced due to a release of the electronically fixed PNRs if the bias is removed. In contrast, at elevated temperatures, a reversible switching of the SAW signal is possible. The switching shows relaxation dynamics that are typical for relaxor ferroelectrics. The relaxation time τ decreases exponentially from several hours at freezing temperature to a few seconds (<5 s) at room temperature.

Hydrogen/Deuterium Dynamics in Hydroxyl Salts Co2(OH)3Br/Co2(OD)3Br Revealed by Muon Spin Relaxation

The temperature-dependent dynamics of the hydrogen/deuterium atoms in geometrically frustrated magnets Co2(OH)3Br and its deuterated form Co2(OD)3Br were investigated by muon spin relaxation (μSR). The deuterium atoms in Co2(OD)3Br were found to be rapidly fluctuating at high temperatures, which should be arising as a quantum atomic effect due to the small mass of deuterium, then they drastically slowed down toward Tc = 250 K where a broad anomaly appeared in the dielectric response, and finally became quasi-static at around 180 K. Meanwhile, the hydrogen atoms in Co2(OH)3Br also exhibited a two-step slowing at ~240 K and ~180 K, respectively. The revealed properties in Co2(OH)3Br/Co2(OD)3Br are reminiscent of relaxor-type ferroelectrics. The present study suggested the effectiveness of the μSR technique on revealing the hydrogen/deuterium (H/D) dynamics in Co2(OH)3Br/Co2(OD)3Br. Furthermore, magnetic coupling was found to be existing at high temperatures in this system. This work provides clear evidence to the mechanism of ferroelectric responses in the hydroxyl salts, i.e., the slowing of protons (deuterium ions) is directly related to the newly revealed ferroelectricity.

Energy storage properties of MgO-doped 0.5Bi0·5Na0·5TiO3-0.5SrTiO3 ceramics

Abstract 0.5Bi 0·5 Na 0·5 TiO 3 -0.5SrTiO 3 -x wt% MgO (x = 0, 0.5, 1.0, 1.5, 2.0, 3.0) ceramics were fabricated via solid-state method. The effect of MgO doped on energy storage properties, dielectric performance, phase structure and microstructures of 0.5Bi 0·5 Na 0·5 TiO 3 -0.5SrTiO 3 (BNST) ceramics were studied systemically. The Mg 2+ substituted Ti 4+ site in BNST, which was confirmed by X-ray diffraction (XRD) result. The scanning electron microscope (SEM) images show that all the ceramic samples exhibit uniform and compact morphologies. The temperature dependent permittivity exhibits frequency dispersion, indicating that the ceramic samples are typical relaxor ferroelectrics. It was found that MgO doped BNST can significant improve the breakdown strength (E b ) of samples from 109 kV/cm to 227 kV/cm, which results in a great enhancement on energy storage density. The sample of x = 3.0 has the largest energy storage density (2.17 J/cm 3 ), which is twice as much as the BNST. Consequently, we consider that MgO-doped BNST ceramics are able to be a promising candidate in the field of pulsed-power devices.

Magnetic and tunable dielectric properties of DyCrO3 thin films

DyCrO3 (DCO) belongs to the family of rare-earth chromites, some members of which exhibit magnetoelectric multiferroic properties. This work characterizes the dielectric tunability in DCO, which is typically, for conventional ferroelectrics, found to maximize near the ferroelectric to paraelectric transition. Two films of DCO were fabricated via a hybrid solution synthesis route on different substrates: one on single crystalline (001) LaAlO3 (LAO) and the other on (001) LAO coated with a conducting LaNiO3 (LNO) layer. The synthesis method resulted in films with both out-of-plane and in-plane texture in the DCO. The lattice mismatch strain between film and substrate caused a slight increase in the Neel temperature of the DCO film on LAO. Transmission electron microscopy images of the DCO film on the LNO/LAO revealed the epitaxial relationship between these phases. The temperature dependence of the relative permittivity showed diffused transition and a frequency dispersion similar to what is observed in typical relaxor ferroelectrics. Isothermal dielectric constant versus dc electric field measurements showed an electric field tunable relative permittivity (i.e., tunability). This tunability reached a broad plateau near the Neel temperature. Such maxima in dielectric tunability are typically observed near a ferroelectric–paraelectric transition, and its proximity to the magnetic ordering temperature in DCO indicates magnetically driven ferroelectricity in this material.

Structure analysis and systematical electric properties investigation of PSN–PMN–PT single crystal

A novel Pb(Sc1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PSN–PMN–PT) single crystal with large size ϕ25 mm × 40 mm was grown by the Bridgman technique. The crystal was cut along [100] orientation with composition of 6PSN–63PMN–31PT, and then its structure and electric properties were investigated systematically. Raman test demonstrates that the crystal is typical relaxor ferroelectrics with perovskite structure. At room temperature, [100]-oriented 6PSN–63PMN–31PT crystal shows the excellent electric properties, such as the dielectric constant er = 4793, the piezoelectric constant d33 = 1237 pC/N, and the remanent polarization Pr = 34.41 µC/cm2, respectively. It is more important that the large coercive field Ec = 8.17 kV/cm in [100]-oriented 6PSN–63PMN–31PT crystal is almost four times than that of PMN–PT, even higher than that of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) and Pb(Lu1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PLN–PMN–PT), indicating its potential application for high-power transducers. With elevating temperature, the [100]-oriented 6PSN–63PMN–31PT crystal shows the large pyroelectric coefficient p = 3.49 × 10−2 C/m2/K at phase transition temperature, and the related figures of merit (FOMs) for current responsivity Fi, for voltage responsivity Fv and for detectivity FD increase from 1.968 × 10−10 m/V, 0.00485 m2/C and 0.59 × 10−5 Pa−1/2 to 1.396 × 10−8 m/V, 0.054 m2/C, and 52.94 × 10−5 Pa−1/2, respectively. Furthermore, the thermal strain at heating process was analyzed for unpoled and poled crystal.

Tuning the ferroelectric transition and magnetic ordering by the polar Ba0.1Sr0.9TiO3 substitution in the multiferroic (1−x) Ba0.1Sr0.9TiO3 - xBiFeO3 (0.2 ≤ x ≤ 0.8) solid solution

Chemical substitution is an effective method for tailoring the electrical and magnetic properties of functional materials. In this work, (1–x)Ba0.1Sr0.9TiO3 - xBiFeO3 (0.2 ≤ x ≤ 0.8) ceramics were prepared by the modified Pechini method. X-ray diffraction patterns manifest that the samples undergo a gradual structural transformation from rhombohedral phase to tetragonal phase with increasing the content of Ba0.1Sr0.9TiO3 (BST). Dielectric properties show that TC can be modulated by the doping level of BST in a wide range from 885 K to 260 K accompanied by the ferroelectric transformation from non-relaxor type to relaxor type ferroelectricity. The room temperature ferroelectricity, ferromagnetism and intrinsic magnetodielectric are observed in the BiFeO3-rich samples. Magnetization and magnetodielectric measurement both show that the spin cycloid is destroyed by the substitution of BST and the critical field for the transition from spiral to antiferromagnetic collinear magnetic structure decreases with increasing the amount of BST. These findings manifest that this materials are quite promising for potential applications in BFO-based magnetoelectric devices and electrocaloric cooling technologies.

Probing the ionic dielectric constant contribution in the ferroelectric phase of the Fabre salts

In strongly correlated organic materials it has been pointed out that charge-ordering could also achieve electronic ferroelectricity at the same critical temperature $T_{co}$. A prototype of such phenomenon are the quasi-one dimensional (TMTTF)$_2X$ Fabre-salts. However, the stabilization of a long-range ferroelectric ground-state below $T_{co}$ requires the break of inversion symmetry, which should be accompanied by a lattice deformation. In this work we investigate the role of the monovalent counter-anion $X$ in such mechanism. For this purpose, we measured the quasi-static dielectric constant along the $c^{*}$-axis direction, where layers formed by donors and anions alternate. Our findings show that the ionic charge contribution is three orders of magnitude lower than the intra-stack electronic response. The $c^{*}$ dielectric constant ($\epsilon'_{c^*}$) probes directly the charge response of the monovalent anion $X$, since the anion mobility in the structure should help to stabilize the ferroelectric ground-state. Furthermore, our $\epsilon'_{c^*}$ measurements %conjugated with earlier investigations of the $c^*$ lattice thermal expansion, show that the dielectric response is thermally broaden below $T_{co}$ if the ferroelectric transition occurs in the temperature range where the anion movement begin to freeze in their methyl groups cavity. In the extreme case of the PF$_6$-H$_{12}$ salt, where $T_{co}$ occurs at the freezing point, a relaxor-type ferroelectricity is observed. Also, because of the slow kinetics of the anion sub-lattice, global hysteresis effects and reduction of the charge response upon successive cycling are observed. In this context, we propose that anions control the order-disorder or relaxation character of the ferroelectric transition of the Fabre-salts.

Structure, dielectric and relaxor properties in lead-free ST-NBT ceramics for high energy storage applications

Abstract (1-x)SrTiO3-x(Na0.5Bi0.5)TiO3 ((1-x)ST-xNBT) ceramics have been prepared by solid-state route and their structure, electric and energy storage properties have been investigated. Dielectric anomalies at Tm and T′m show strong frequency dispersion as the typical relaxor ferroelectrics behavior over a broad temperature range. The Tm of (1-x)ST-xNBT ceramics dramatically shifted to a higher temperature (from −118 °C to 106 °C at 1 kHz) with increasing x. All samples showed the broad relaxor behavior due to the increase in the degree of lattice disorder and the thermal evolution of PNRs, and exhibited a discharge energy density of more than 1.18 J/cm3. The x = 0.4 sample exhibited a maximum discharge energy density of 1.70 J/cm3, consistent with the high value of Eb (∼21 kV/mm) and Pm (∼25 μC/cm2). The results indicate that (1-x)ST-xNBT ceramics might be a promising environmental friendly material for energy storage application.

Impedance spectroscopy and ferromagnetic properties of Bi0.8Gd0.2FeO3 multiferroics

Multiferroic Bi0.8Gd0.2FeO3 (BGFO) ceramics were prepared by a rapid-liquid phase sintering process. BGFO ceramics can be sintered at a sintering temperature range of 875°C–940°C and shown a pure orthorhombic (space group, Pnma) structure. The crystal symmetry and lattice parameters were determined from the Rietveld analysis for the experimental data. BGFO ceramics sintered at 900°C exhibited high theoretical relative density (∼98%), strong ferroelectricity and good magnetism. BGFO ceramics exhibited the similar dielectric relaxation properties to the typical relaxor ferroelectrics. The role of oxygen vacancies at high temperature in dielectric and ac conductivity behavior was also discussed. The diffusing of structure defects between the grain and grain boundary was established using Impedance Spectroscopy (IS).

Electric field induced relaxor behavior in anisotropically strained SrTiO3 films

Electric fields can modify the dielectric response of ferroelectric and especially relaxor ferroelectric material. Since strained ferroelectric fields represent ideal candidates for relaxor ferroelectrics, we analyzed the impact of ac and dc electric fields and field orientation on the dielectric properties of anisotropically strained epitaxial SrTiO3 films in detail. The tensile strain in the SrTiO3 films causes an increase of the ferroelectric-dielectric phase transition temperature to 258K and 288K for small and large tensile strains, respectively. The resulting films represent relaxor-type ferroelectrics with properties that strongly depend on the applied electric field. While a dc bias field significantly suppresses the permittivity in the paraelectric regime ranging from 180K to 320K, an ac field leads to an even more pronounced enhancement of the permittivity in an even larger temperature regime (e.g. reduction of up to 50% versus enhancement of up to 380% for 0.5V/μm dc bias or ac field, respectively). Furthermore the ac field dependence is nonlinear and cannot be explained by the classical Rayleigh law. Frequency dependent measurements show among others that the electric field dependences are strongly related to the relaxor-type behavior. The different dielectric responses are explained in terms of the mobility and dynamic of regimes of uniform polarization, the polar nanoregions, that are generally assumed to be responsible for the relaxor behavior.

Proving relaxor-type ferroelectricity in Pr-doped SrTiO3by XRPD

Proving relaxor-type ferroelectricity in Pr-doped SrTiO₃by XRPD

Suppressed ferroelectric relaxor behavior of Mn‐modified Ba(Zr0.3Ti0.7)O3 relaxor ceramics

MnCO3‐modified Ba(Zr0.3Ti0.7)O3 relaxor ferroelectric ceramics were fabricated by using the solid‐state reaction method. The temperature dependences of electrical and dielectric properties of the ceramics were systematically investigated over the range −140 to 400 °C. The typical ferroelectric relaxor behavior of the Ba(Zr0.3Ti0.7)O3 ceramics was greatly suppressed by adding a proper amount of MnCO3. The suppressed relaxor behavior can be restored by annealing the samples in air, which is attributed to the presence of oxygen vacancies in the samples. In the paraelectric phase region, the low‐frequency dielectric relaxations associated with oxygen vacancies are observed above room temperature, and increase with increasing of Mn content. Compared to the undoped Ba(Zr0.3Ti0.7)O3 ceramic, Mn‐doped samples display excellent temperature stability in a wide temperature. The critical composition of x = 0.05 (MnCO3) not only exhibits a lower degree of ferroelectric relaxor behavior (ΔTm = 5.6 K), but also maintains a relatively higher tunability (66.9%@30 kV cm−1) than that of pure Ba(Zr0.3Ti0.7)O3 (ΔTm = 16.5 K, 49.6%@30 kV cm−1).