Temperature Of Dielectric Maximum Research Articles

Interfacial strain induced giant magnetoresistance and magnetodielectric effects in multiferroic BCZT/LSMO thin film heterostructures

Layered thin films of the ferroelectric perovskite Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) and the ferromagnetic half-metal La0.80Sr0.20MnO3 (LSMO) are well-known multiferroic systems that show promise for spintronic applications. In this work, the structure–property relationships are explored in novel BCZT/LSMO thin film heterostructures with optimized ferroic properties. Epitaxial BCZT/LSMO thin film heterostructures are grown by varying the lattice mismatch strains on single crystal LaAlO3 (LAO) (100) and MgO (100) substrates using the pulsed laser deposition technique. The epitaxial strain in the films gives rise to a tetragonal distortion of the BCZT and LSMO unit cells and significantly affects their magnetotransport and magnetodielectric properties. The BCZT/LSMO/LAO heterostructure exhibits a colossal magnetoresistance effect due to a large out-of-plane tensile strain, which induces enhanced carrier hopping in the LSMO layer as compared to the BCZT/LSMO/MgO film. The larger tetragonal distortion of the BCZT unit cell in BCZT/LSMO/MgO contributes to higher dielectric permittivity, with a greater dielectric maxima temperature and freezing temperature. Magnetodielectric measurements reveal a hitherto unobserved giant magnetodielectric effect in the BCZT/LSMO/MgO film, attributed to a large in-plane strain, which induces interfacial polarization distortion at the interfacial layer. Overall, this work elucidates the unique strain and charge-mediated cross-coupled phenomena of magnetic and electric orders in multiferroic thin film heterostructures, which are critical for their technological applications.

Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering.

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi0.5(Na0.8K0.2)0.5TiO3-xBi0.2Sr0.7TiO3 (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature Tm and inducing the formation of highly dynamic polar nano-regions. In addition, the Tm shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered Tm with relaxor properties synergistically contribute to a high Pmax and low Pr, improving the breakdown strength with BST and resulting in a high recoverable energy density Wrec of 0.81 J/cm3 and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Low-Temperature Sintering of Bi(Ni0.5Ti0.5)O3-BiFeO3-Pb(Zr0.5Ti0.5)O3 Ceramics and Their Performance.

A low-temperature sintering strategy was realized for preparing 0.21Bi(Ni0.5Ti0.5)O3-0.05BiFeO3-0.74Pb(Zr0.5Ti0.5)O3 (0.21BNT-0.05BF-0.74PZT) ceramics by conventional ceramic processing by adding low melting point BiFeO3 and additional sintering aid LiBO2. Pure perovskite 0.21BNT-0.05BF-0.74PZT ceramics are prepared at relatively low sintering temperatures, and their structure presents tetragonal distortion that is affected slightly by the sintering temperature. The 1030 °C sintered samples have high densification accompanied by relatively large grains. All ceramics have excellent dielectric performance with a relatively high temperature of dielectric constant maximum, and present an apparent relaxation characteristic. A narrow sintering temperature range exists in the 0.21BNT-0.05BF-0.74PZT system, and the 1030 °C sintered 0.21BNT-0.05BF-0.74PZT ceramics exhibit overall excellent electrical performance. The high-temperature conductivity can be attributed to the oxygen vacancies' conduction produced by the evaporation of Pb and Bi during sintering revealed by energy dispersive X-ray measurement.

Non-trivial Behavior of Temperature of Dielectric Constant Maximum in (Pb/La)(Zr/Ti)O3 9/65/35 Relaxor Ferroelectric Ceramics Detected by Acoustic Emission

9/65/35 PLZT relaxor was studied under a bias electric field using the acoustic emission method. It was established that the temperature of smeared dielectric constant maximum exhibits the V-shape, lying fully within the ergodic phase, as well as that the threshold electric field is found to be approximately the same as in both PMN-0.24PT and PFN-0.02PT relaxors. A reason of the latter phenomena is discussed from the viewpoint of incorporated ions properties.

Dielectric properties and relaxor behavior of (1-x)Ba(Zr0.15Ti0.85)O3 - xBa(Mg(1⁄3)Nb(2⁄3))O3 ceramics for capacitor applications

The Ba(Zr0.15Ti0.85)O3 (BZT) ceramics were fabricated by the conventional solid-state method and the impact of Ba(Mg(1/3) Nb(2/3))O3 (BMN) addition into the BZT matrix on their microstructure, dielectric and ferroelectric properties were examined. According to the XRD analysis, the (1-x)Ba(Zr0.15Ti0.85)O3-xBa(Mg(1⁄3)Nb(2⁄3))O3 ceramics retain a pseudo-cubic ABO3 perovskite structure with an apparent decrease in c/a ratio as x increases. The SEM images show that the BZT-BMN ceramics instigate the reduction of the average grain sizes. And as the BMN content increases to 0.01, the Mg2+ and Nb5+ ion substitutions in the B-sites greatly improved the dielectric constant of BZT ceramics at room temperature. The frequency dispersion of the dielectric constant and the diffuseness of phase transition for BZT-BMN ceramics are enhanced by increasing the BMN addition. In the modified BZT ceramics, the dielectric maximum temperature (Tm) is reduced as the BMN content increases, and the temperature stability of the permittivity is modified by BMN addition. The hysteresis loop grows thinner and the remnant polarization, as well as coercive field, is greatly reduced as the BMN addition increases.

Influence of weak ac electric field on the temperature of dielectric maximum of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 relaxor ferroelectric single crystals based on acoustic emission data studies

(1-x)PbMg1/3Nb2/3O3-xPbTiO3, [100]-oriented relaxor ferroelectric crystals were studied by means of dielectric and acoustic emission methods in dependence on temperature and under ac measuring electric field with several values and frequencies. The dependence of temperature of dielectric constant maximum on and without ac field value and frequency was plotted. Also a scatter of the temperature of dielectric constant maximum was calculated in dependence on ac field frequency. Such the phenomenon was discussed from a point of view of growth of the polar nanoregions on cooling.

Relaxor ferroelectric and dielectric properties of (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 ceramics

The environmentally-friendly (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 (x=0, 0.02, 0.04, 0.06, 0.08) relaxor ferroelectric ceramics were prepared by the conventional solid-state method and sintered in air at 1400 °C for 2 h. SEM and XRD analyses were utilized to study the surface morphologies and the crystalline structures, respectively. The effects of Ba(Mg1/3Ta2/3)O3 on the phase transformation, dielectric and ferroelectric properties of Ba(Zr0.1Ti0.9)O3 ceramics were also investigated. It is found that the average grain size of (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 (BZT–BMT) perovskite single-phase ceramics decreases as the content of Ba(Mg1/3Ta2/3)O3 (BMT) increases. The relaxor ferroelectric behavior with diffuse phase transition and well-defined frequency dispersion of dielectric maximum temperature is found for the ceramic with increasing x values. 0.98BZT–0.02BMT ceramic shows very good dielectric properties with the relative permittivity and the dielectric loss, measured at 100 kHz as 6034 and 0.01399 respectively at room temperature. Both remnant polarization and coercive field decreased with increasing BMT content, indicating a transition from the ferroelectric phase to the paraelectric phase at room temperature.

Grain-size-insensitive dielectric properties of Sr0.6Ba0.4Nb2O6 relaxor ferroelectric ceramics with tetragonal tungsten bronze structure

The influence of grain size on the dielectric properties of Sr0.6Ba0.4Nb2O6 (SBN60) ceramics with a tetragonal tungsten bronze structure was examined. The conventional and two-step sintering procedures were used to fabricate dense and phase-pure SBN60 ceramics with grain sizes ranging from 2.2 μm to 17.3 μm. In the temperature dependence of the dielectric permittivity, all samples showed a relaxor-like broad dielectric peak with a maximum at around 60 °C. The maximum dielectric permittivity and dielectric maximum temperature of the SBN ceramics were found to be less dependent on the grain size. The reason for the grain-size-insensitive dielectric properties of the SBN60 ceramics is discussed based on the analysis of the dielectric properties and Raman spectra.

Fabrication of (Bi0.5K0.5)TiO3 modified BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 piezoelectric ceramics

The lead-free x(Bi0.5K0.5)TiO3-0.23BaTiO3-0.02Bi(Mg0.5Ti0.5)O3-(0.75-x)BiFeO3 piezoelectric ceramics (x = 0.05, 0.07, 0.09, and 0.11) were prepared by solid-state reaction method. The increase of (Bi0.5K0.5)TiO3 concentration revealed a decrease of dielectric maximum temperature (Tm), however, the values were higher than 420 °C. The Rietveld structure refinement for each composition showed pseudo-cubic symmetry and the rhombohedral distortion (90 - αF) was gradually decreased from 0.27° to 0.09° for x = 0.05 and 0.11, respectively. The saturation and remanent polarization were increased and a coercive field was decreased, while the critical exponent (γ) was increased from 1.407 (x = 0.07) to 1.821 (x = 0.11) revealing more relaxor-like behavior with higher (Bi0.5K0.5)TiO3 content. The remanent polarization, coercive field, and piezoelectric strain constant of 31.9 μC/cm2, 23.6 kV/cm, and 315 pm/V, respectively, obtained in the composition with x = 0.11 are significantly higher than those reported previously for other Bi-based piezoelectric ceramics with Tm>250 °C.

Crossover from normal to relaxor ferroelectric in Sr0.25Ba0.75(Nb1−xTax)2O6 ceramics with tungsten bronze structure

The crossover from normal to relaxor ferroelectrics in Sr0.25Ba0.75(Nb1−xTax)2O6 (x = 0, 0.1, 0.25, and 0.5) ceramics was determined together with the structure evolution. A single-phase tungsten bronze structure in space group P4bm (x = 0 and 0.1) or P4/mbm (x = 0.25 and 0.5) was obtained in the entire composition range. The lattice parameter a increased, while c, tetragonality c/a, and cell volume decreased with increasing x. Meanwhile, the dielectric maximum temperature Tm went down and the dielectric peak exhibited an enhanced diffused nature with a stronger frequency dispersion, where the saturated P–E loop (x = 0 and 0.1) transformed to a slim relaxor loop (x = 0.25) and finally to the linear one (x = 0.5). Raman spectra results revealed the reduced covalence between the B-site cation and the oxygen ion as a result of Ta-substitution. The coexistence of Nb5+ and Ta5+, which possessed the distinct covalence with the oxygen ion, played the key role in the structural variation and crossover from normal to relaxor ferroelectrics in the present system.

Significantly improved dielectric and piezoelectric properties of BiAlO3 modified potassium bismuth titanate lead-free ceramics

The effects of BiAlO3 content on the crystal structure, microstructure, dielectric, and piezoelectric properties of (1-x)(K0.5Bi0.5)TiO3-xBiAlO3 (abbreviated as KBT-BA) (x = 0–0.05) ceramics were systematically studied. Rietveld refinement of XRD data revealed a decrease in tetragonality and an increase in weight fraction of the cubic phase with the increase in BiAlO3 incorporation. The frequency-dependent temperature of dielectric maximum (Tm) was found to increase from 351 °C for pure KBT to 372 °C (at 1 MHz) for 1% BA doped unpoled sample. An increasingly diffuse dielectric anomaly and strengthening of relaxor behavior were noticed in KBT-BA solid-solution with the increase in BA content. Temperature dependence of DC conductivity followed Arrhenius behavior, and the activation energies were found to be in 0.98 ± 0.03 eV to 1.18 ± 0.02 eV range for all compositions. The piezoelectric charge coefficient (d33) was found to be 109 pC/N for 5% BiAlO3 doped sample, which is ~ 80% higher than that of pure KBT.

Electrocaloric effect of alkali co-substituted Sr0.6Ba0.4Nb2O6 ceramics

We have investigated the electrocaloric properties of K+ and Na+ co-substituted Sr0.6Ba0.4Nb2O6 (SBN) ceramics using the indirect method. Tetragonal tungsten bronze (K0.5Na0.5)2x(Sr0.6Ba0.4)5-xNb10O30 (KNSBN) with x = 0.24 was synthesized using dual-step sintering. Despite the low amount, K+ and Na+ co-substitution resulted in normal ferroelectric behaviour, showing no significant shift in the dielectric maximum temperature of 111 °C with increasing frequency. Maximum electrocaloric temperature change (ΔT) of 0.3 K was observed at an electric field of 30 kV/cm (ΔE) yielding the largest electrocaloric responsivity (ΔT/ΔE) among SBN based ceramics. This relatively large value is in agreement with the larger pyroelectric coefficient of KNSBN compared to SBN based ceramics.

Acoustic anomalies and relaxation dynamics of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals studied by using Brillouin spectroscopy

Acoustic anomalies of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals were investigated over a wide temperature range from −196 °C to 900 °C by using Brillouin spectroscopy. The longitudinal sound velocity, the acoustic absorption coefficient and the elastic constant C11 were determined for the acoustic phonon mode propagating in the [100] direction. Two acoustic anomalies, weaker ones at the cubic-tetragonal phase transition temperature of ~540 °C and more pronounced ones at temperatures near 315 °C near the dielectric maximum temperature, were investigated and discussed in relation with the relevant order parameters coupled to the acoustic waves. The relaxation dynamics in the cubic phase were studied based on the flattening of the mode frequency and the half width, which was observed for the first time, and a modified Arrhenius law.

T* of Relaxor Ferroelectric (1 − x) Pb(Zn1/3Nb2/3)O3‐xPbTiO3 Single Crystals Revisited Using Brillouin Spectroscopy

The relaxor characteristics of Pb[(Zn1/3Nb2/3)1–xTix]O3 (PZN‐xPT) single crystals (with x = 0 and x = 0.08) are investigated using temperature‐dependent Brillouin scattering spectroscopy. The longitudinal acoustic (LA) mode shows typical relaxor behaviors for PZN, whereas its mode frequency exhibits a discontinuous change at the phase transition temperature (TC) for PZN‐8%PT. The transverse acoustic (TA) mode, which is forbidden in an ideal cubic phase at the backscattering geometry, appears in both samples at a certain temperature above either the dielectric maximum temperature (Tm) or TC. This breakdown of the Brillouin selection rule in the cubic phase indicates that the noncubic polar regions become appreciable at this temperature where the interaction between the acoustic waves and the polar nanoregions (PNRs) is strong enough to enable the appearance of the TA mode. The intermediate characteristic temperature T* is determined in terms of the minimum of the temperature derivative of the half width of the LA mode, and the values are nearly the same as those determined via the acoustic emission signal measurements. These comparisons reveal the universal feature of the local phase transformation from dynamic to quasistatic PNRs at T*, giving rise to the appearance of the TA mode.

(Bi1/2K1/2)TiO3–SrTiO3 solid-solution ceramics for high-temperature capacitor applications

The relaxor state of (Bi1/2K1/2)TiO3 exhibits promising dielectric properties for high-temperature capacitor applications, but the spontaneous phase transition into the low-temperature ferroelectric state and the excessively high dielectric maximum temperature (Tm) at around 360 °C are the main drawback to this material. In this study we examined solid solutions of (Bi1/2K1/2)TiO3 with SrTiO3 to improve the temperature stability of the dielectric properties. As precursors to fabricate the sold-solution ceramics, fine powders of (Bi1/2K1/2)TiO3 and SrTiO3 were both synthesized by the hydrothermal method. Dense (1 − x)(Bi1/2K1/2)TiO3–xSrTiO3 ceramics with x up to 0.5 were then obtained by reaction sintering of the powders. A crystal structure analysis revealed that the average symmetry of the solid-solution ceramics changes from tetragonal to cubic with increasing the SrTiO3 content. Dielectric measurements showed that the incorporation of SrTiO3 into (Bi1/2K1/2)TiO3 stabilizes the relaxor state to shift Tm largely toward lower temperatures. As a result, the sample with x = 0.5 exhibited a temperature-stable dielectric permittivity of 1700 ± 15% over a wide temperature range from room temperature up to 260 °C. The electric-field and temperature dependences of the energy-storage properties of the sample were also investigated.

Anomalous behaviors of elastic constants of lead-free piezoelectric (Na1/2Bi1/2)TiO3-5%BaTiO3 single crystals studied by Brillouin spectroscopy

The acoustic properties of unpoled (Na1/2Bi1/2)TiO3-5%BaTiO3 (NBT-5%BT) lead-free single crystals were investigated over a wide temperature range from 740 °C to room temperature. Temperature dependences of sound velocities, acoustic attenuation coefficients, and independent elastic constants were determined by using Brillouin spectroscopy. Among the three symmetrized eigen elastic constants C44, (C11 − C12)/2, and C11 + 2C12, (C11 − C12)/2 was the smallest and showed the largest softening at high temperatures above the dielectric maximum temperature (Tm). The softening of (C11 − C12)/2 resulted in the substantial increase of the elastic anisotropy parameter defined as 2C44/(C11 − C12). This suggested that the local symmetry and the associated structural instability of local polar distortions were tetragonal. The onset temperature of quasistatic dynamics of polar nanoregions was ∼500 °C at which all four attenuation coefficients began to increase noticeably. The broad and diffused acoustic anomalies indicated that the low-temperature phase is a typical relaxor state without any long-range order. However, the noncubic local distortions at low temperatures seem to drive the average symmetry of NBT-5%BT to deviate from the cubic phase because the premise of three independent elastic constants for the ideal cubic phase was no longer valid below Tm.

Effect of Mn doping on the acoustic and vibrational behaviors of lead-free piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 single crystals

The acoustic and vibrational properties of Mn-doped (Na1/2Bi1/2)TiO3-xBaTiO3 with x = 0.05 were investigated by using Brillouin and Raman spectroscopies and compared with those of undoped crystals. The mode frequency and the half width of the Brillouin doublet of the longitudinal acoustic mode showed more drastic changes near the dielectric maximum temperature compared to the broad and diffused changes of the undoped crystals, which indicates that Mn-doping induces polar domains larger than the typical polar nanoregions formed in undoped counterpart. The acoustic anomalies were most pronounced along the <100> direction suggesting that the polarization fluctuations are anisotropic and largest along this direction. Temperature dependence of Raman spectra showed that there are two characteristics temperatures where mode splitting occurs due to local symmetry changes. The high-temperature anomaly was associated with the changes in the acoustic properties, while the low-temperature mode splitting was related to the dielectric anomaly near depolarization temperature.

Microstructure and ferroelectric properties under various temperatures of (1 – x)Pb(Zr0.52Ti0.48)O3 -xCa3Co4O9 composite materials

While controlling atomic positions in mixed phases in composite materials is difficult, electrical coupling of the different phase components is attractive. This research studied effects of misfit layered structure added into perovskite structure in order to investigate microstructure and ferroelectric properties of Pb(Zr0.52Ti0.48)O3 (PZT) and Ca3Co4O9 (CCO) composites. The composite materials of PZT-CCO showed a small proportion of monoclinic phase that was found to strongly influence the PZT phase. The microstructure exhibited heterogeneity of PZT and CCO. FE-SEM showed that grain size decreased with increasing CCO content. Co atoms migrated towards center of curved grain boundaries. The charge carriers of CCO affected domain wall movements in the PZT under high temperature. Dielectric maximum temperature alternated due to the affected charge mechanism in the CCO. Polarization-electric field loops revealed that saturated polarization and domain switching decreased with increasing CCO content and temperatures. Capacitive and resistive behaviors as well as remanent polarization were increased with increasing CCO content at high temperatures. Electric field was accounted for current density causing leakage current. It is expected that the PZT-CCO composite materials developed will have electrical performance suitable for some electronic devices.

High electrostrictive properties and energy storage performances with excellent thermal stability in Nb-doped Bi0.5Na0.5TiO3-based ceramics.

As a promising candidate material replacing Pb(ZrTi)O3 (PZT), the lead-free Bi0.5Na0.5TiO3 (BNT) system exhibits outstanding piezoelectric and ferroelectric properties. However, the weak thermal stability of these electric properties hampers its practical applications. In this work, we designed and prepared novel Nb-doped 0.76Bi0.5Na0.5TiO3–0.24Bi0.5K0.5TiO3 (BNT–BKT) ceramics with superior temperature stability of electric properties. Both strain as well as discharging properties of 5% Nb-doped BNT–BKT ceramics varied less than 3% and 12.5% respectively from room temperature to 160 °C, ascribed to the enlarged gap between the depolarized temperature (Td or TF–R) and the maximum dielectric temperature (Tm). In addition, we investigated the impacts of Nb doping on the phase transition, dielectric, piezoelectric and ferroelectric behaviors of BNT–BKT ceramics in detail. Temperature dependent dielectric spectrums indicated that Td decreased below room temperature with Nb modifying, revealing that the phase structure transformed from ferroelectric into ergodic relaxor. Accordingly, the maximum strain value of 0.21% and recoverable energy storage of 1.2 J cm−3 were simultaneously acquired at the critical composition of 5% Nb incorporation. Our results provide an effective means of obtaining BNT-based ceramics with simultaneously thermally stable strain and discharge properties for wide temperature actuator and capacitor applications.

Effect of Poling Electric Field and Temperature Change on the Dielectric Anomalies of Relaxor Ferroelectric Strontium-Barium-Niobate Single Crystals

The dielectric properties of the uniaxial relaxor ferroelectric SrxBa1−xNb2O6 with x = 0.75 were investigated along the polar [001] direction as a function of temperature. The capacitance maximum showed the frequency dispersion commonly observed in relaxors. Additional weak dielectric anomalies were observed in the paraelectric phase; they were only seen during the heating process and disappeared upon subsequent cooling. These were attributed to the existence of large polar clusters strongly pinned at defects and/or to random fields and their metastable characters. Aligning the ferroelectric domains along the polar axis at room temperature removed the high-temperature dielectric anomalies. The dependences of the capacitance and the dielectric maximum temperature on the magnitude of the poling field were investigated.