Ferroelectric Hysteresis Loops Research Articles

Effects of Ba2+doping on microstructure and properties of PLMNT electro-optic ceramics fabricated by hot-pressed sintering process

A series of highly transparent electro-optic (EO) ceramics Pb0.975-xBaxLa0.025(Mg1/4Nb1/2Ti1/4)0.99375O3 with the Ba2+ content of 0, 0.005, 0.01, 0.02, 0.04 were fabricated through the vacuum/oxygen hot-press sintering process. The effects of the barium substitution on the material phase transition, transmittance, dielectric, ferroelectric and electro-optic properties have been investigated and analyzed. With the Ba2+ content increasing, the shape of the ferroelectric hysteresis loop changed from rectangular to slim, the values of remnant polarization (Pr) and coercive electric field (Ec) decreased obviously. The maximum reduction of Pr can reach up to ∼89.8%. All the samples present the high transparency of ∼68% in the near infrared wavelength. The quadratic EO coefficients declines slightly while the Ba2+ content increasing. When the x is 0.01, the sample shows a relatively larger quadratic EO coefficient of ∼30.42 × 10−16 (m/V)2 and a lower Pr value of ∼2.08 μC/cm2, which promise the material a hopeful application in EO modulator.

Unexpected wide tuning of ferroelectric properties by varying the Er concentration in La2-xErx(MoO4)3 (x = 0.75, 1, 1.25) solid solutions

Powder samples of the series La2-xErx(MoO4)3 (x ​= ​0.75, 1, 1.25) were prepared by solid-state reaction from the La and Er trimolybdates. The correlation of the ferroelectric properties with the crystal structure, as a function of the x concentration, was studied by X-ray diffraction (XRD), dielectric and optical spectroscopy, and the ferroelectric hysteresis loop measurements. The β′-Gd2(MoO4)3 structure type was identified by a non-conventional Rietveld method, including a symmetry analysis. Contrary to the expectations, the ferroelectric properties were intensified by the Er3+ concentration increase: the maximum polarization for x ​= ​1.25 reaches one order of magnitude larger than that of x ​= ​0.75, and the Curie temperature increase was around 200 ​K. This unexpected behavior is opposite of that observed for the improper ferroelectrics RE2(MoO4)3, where the ferroelectric properties are enhanced with the RE ionic radius increase. Hence, the series La2-xErx(MoO4)3 show an “wider tuning range” for ferroelectric properties opposite to the rare earth trimolybdate family.

Examining imprinted ferroelectric hysteresis loops and improved energy storage properties of Mn-doped epitaxial SrTiO3 thin films using heat treatment

This study investigated imprinted ferroelectric hysteresis loops and energy storage properties of Mn-doped epitaxial SrTiO3 (MSTO) thin films using heat treatment. The crystallinity of MSTO thin films was improved by reducing the deposition rates of epitaxial (001) MSTO thin films on single-crystal (100) Rh substrates from 0.15 to 0.03 nm/pulse. The polarization of MSTO thin films, with improved polarization by Mn doping, was further enhanced by improving film crystallinity. MSTO thin films exhibited an energy storage efficiency of approximately 90 % and an increase in energy storage density from 23 to 34 J/cm3. The energy storage density increased further to 39 J/cm3 using imprinted ferroelectric hysteresis loops and heat treatment.

Preparation of nanoscale [(Ba0.85Ca0.15)0.995Nd0.005](Ti0.9Hf0.1)O3 ceramics via hydrothermal method and effect of grain size on multifunctional performance

Nanoscale [(Ba0.85Ca0.15)0.995Nd0.005](Ti0.9Hf0.1)O3 (Nd-BCTH) ceramics were prepared via the hydrothermal method, and the effects of sintering temperature and holding time on the phase structure, micromorphology, electrical and optical properties of the Nd-BCTH ceramics were explored. All the Nd-BCTH ceramics present rather pure perovskite structure with composition approaching rhombohedral phase around the morphotropic phase boundary (MPB) region. The highest relative density is obtained for the sample sintered at 1220 °C for 10 h. The existence of Ba2+, Ca2+, Ti4+, Hf4+ and Nd3+ is confirmed and the elements distribute rather uniformly detected by X-ray photoelectron spectrometer (XPS) and energy dispersive X-ray (EDX) analysis. The ceramics present nanoscale grain size, which tends to increase with the increase of sintering temperature and holding time, and significantly affects dielectric constant and Curie temperature. Very thin and narrow ferroelectric hysteresis loops are observed, where a considerable energy storage density (173.88 mJ/cm3) and high energy storage efficiency (80.68%) are obtained at low electric field. The increase of sintering temperature and holding time induces a red shift at 400 nm absorption edge and a blue shift at 300 nm absorption edge in the Nd-BCTH ceramics, and all ceramics have a maximum absorption value at around 260 nm. Under the excitation of 269 nm light, the Nd-BCTH ceramics show the strongest fluorescence peak at 473 nm, corresponding to the 4G3/2→4I9/2 transition, emitting indigo blue fluorescence. When the ambient temperature is above 400 °C, grains conduction dominates the conductive mechanism in the nano-sized Nd-BCTH ceramics. Such conduction can be attributed to oxygen vacancies caused due to the evaporation of alkaline-earth metals during high temperature sintering, and show typically thermally excited relaxation process.

Multifunctionality of rare earth doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 ferroelectric ceramics

Undoped and RE3+ (RE: Pr; Nd; Dy; Ho; Tm) doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 (NBTKN0.075/NBTKN0.075-RE) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed a pure perovskite structure without secondary phases. The Ho, Dy and Tm ions revealed a dielectric curve with a more diffused phase transition associated with a high value of the dielectric constant, while the lowest diffusivities were found for the Nd and Pr ions doped NBTKN0.075. The ferroelectric hysteresis loops show the significant increase of polarization and electric breakdown strengths (BDS) in all doped samples, accompanied by P–E shape changes under the influence of the different RE3+ ions. In the optical studies, the conversion of near- infrared light to visible light was investigated for Ho3+ and Dy3+ doped NBTKN0.075. The sample with Ho3+ produced a strong green-yellow up-conversion (UC) emission. At an excitation of λex = 800 nm, the blue-green UC emission of the Dy ion showed that the UC is due to the energy transfer interaction. CIE diagram with the corresponding (x, y) coordinates were used to clearly identify the overall color of the multichromatic spectral emissions in each spectrum. The additional functionality of up-conversion emission in the ferroelectric NBTKN0.075-RE material, and its positive effects on the electrical proprieties, open the possibility to realize multifunctionality in a wide range of applications.

Large magnetoelectric effect in BaFe12O19-(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 particulate composite

Multiferroic composites with a large magnetoelectric response are gaining attractive interests for the design of magnetoelectric (ME) functional devices. In this work, the particulate ME composites (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–xBaFe12O19 (x=0, 0.1, 0.2, 0.3, 0.4 and 1) were prepared, and their structural, dielectric, magnetic, ferroelectric, piezoelectric properties and magnetoelectric coupling were systematically investigated. The composites consisted of only two chemically separated phases with well-bonded interface. Dielectric and impedance analyses indicated the co-contribution of grain and grain boundary to polarization. Well-saturated ferroelectric and magnetic hysteresis loops demonstrated multiferroic nature. ME response was investigated elaborately by employing magnetically induced polarization, together with measuring ME voltage coefficient and magnetodielectric value. Specifically, a large ME coefficient of 26.78 ​mV/cm·Oe was achieved for x=0.3, which is higher than that in single-phase BaFe12O19 and its coupled composites.

Significant improvement in electrical characteristics and energy storage performance of NBT-based ceramics

Dielectric capacitors with superior power density and ultra-fast charge/discharge capability have attracted growing attention in the pulse power field. In this work, rare earth oxide (Sm2O3) was introduced into (0.74Na0.5Bi0.5-0.26Sr)Ti0.9Zr0.1O3 matrix, to enhance the comprehensive energy storage performance. The structure, dielectric and ferroelectric characteristics of these materials were systematically studied, to assess the potential application in multilayer ceramic capacitors. All samples yielded a perovskite structure, as the addition of Sm2O3 results in a substantial increase in density, along with the enhancement of relaxor behavior and local nanodomains. With increasing Sm2O3 concentration, a distinctly slim ferroelectric hysteresis loop as well as frequency dispersive dielectric characteristics have been detected. The NBSZT-0.02Sm ceramic has realized an excellent energy storage density of 4.62 J/cm3, with a moderately good energy efficiency of 84.38% and favorable temperature stability over a broad temperature range of 102.7–397.1 °C. The activation energy (Ea) of the ceramics increased from 1.40 eV to 1.72 eV with Sm2O3 concentration increasing from x = 0 to x = 0.04, which inhibits the appearance of the local electrical branch and thus improves the breakdown strength of the NBSZT-xSm ceramics. This study provides a novel possibility for designing lead-free ceramic materials for high-temperature capacitors.

Role of Sr+2 ions substitution on structural and multiferroic properties of BiFeO3 nanoparticles

The multiferroic nanoparticles Bi1−xSrxFeO3 (BiSrFeO3) were prepared by performing ceramic method; (0.10 ≤ x ≤ 0.25). Nanostructure and multiferroic properties of the synthesized materials were studied. BiSrFeO3 is a single-phase hexagonal-rhombohedral crystal structure as evidenced by X-ray diffraction (XRD) patterns. It has been found that all BiSrFeO3 nanoparticles are ferroelectric materials. The ferroelectric properties of BiFeO3 changed when Sr2+ ions were substituted. At x = 0.25 mol%, Sr2+ ions lead to the magnetization development of BiFeO3. At room temperature, the remnant magnetization increased from its initial value. A BiSrFeO3 multiferroic nanoparticles system exhibits both ferroelectric and ferromagnetic hysteresis loops. These results depict that the present samples can be regarded as a promising candidate for designing energy storage devices.

Enhanced energy-storage properties of La2O3 doped (Na0.5Bi0.5)0.705Ba0.045Sr0.25TiO3 lead-free ferroelectric ceramics

The powder samples of (Na0.5Bi0.5)0.705Ba0.045Sr0.25TiO3-xLa2O3 (NBBSLT) have been prepared successfully by a wet solid-phase method. The effects of La doping on the morphology, ferroelectric and dielectric properties of NBBSLT ceramics were studied. XRD results show that the composite has perovskite structure. The dense phase morphology of NBBSLT was observed by SEM. Dielectric measurements show that depolarization temperature and Curie temperature move toward low temperature. With the increase of La content, the ferroelectric hysteresis loops at room temperature become thinner at first and then wider. The NBBSLT ceramics have excellent energy storage properties when the La content is 0.04.

Study of the structural, ferroelectric and dielectric properties of BaTiO3 co-doped with Sn4+ and Cr3+

In the present work, we studied the effect of Sn4+ and Cr3+ doping on the structural, ferroelectric, and dielectric properties of BaSnxCryTi1−(x+y)O3. The materials were prepared by a combination of high-energy mechanical milling and solid-state reactions. The X-Ray Diffraction (XRD) analysis and Rietveld refinements confirmed the presence of a single tetragonal phase for the pure and doped samples. The SEM study revealed that the microstructure is highly susceptible to the addition of both dopants, causing an evident grain refinement. On the other hand, the addition of Sn4+ and Cr3+ had a strong influence on ferroelectric properties, as observed by the pinching of the ferroelectric hysteresis loops. The addition of Sn4+ increases the remnant and maximum polarization, as the Cr3+ doping promoted the contrary effect. Co-doping with Sn4+ and Cr3+ resulted in a maximum energy storage value of 0.2574J/cm3 with a efficiency of up to 65%, overcoming the values of pure BT. The relative permittivity of all doped samples remained in values of ∼1000, just a little below the permittivity of pure BT.

Domain configuration and domain switching in Dy-doped 0.72PMN-0.28PT Piezoceramics with high d33 coefficient

The PMN-28PT-xDy (x = 0, 1, 2, 3 and 4%) piezoelectric ceramics were prepared by the two-step sintering method. A high piezoelectric coefficient d33 ∼ 1270 pC/N is achieved when x = 3%. As the Dy doping content increases, the domain configuration transforms from ordered stripe-domains to disordered watermark-domains, while the average domain size decreases evidently from ∼635 nm to ∼100 nm. The domain switching was investigated through strain curves and ferroelectric hysteresis loops measured at different electric field amplitudes and frequencies. To fully polarize the PMN-28PT-xDy ceramics, the electric field amplitude was found better be higher than 2.5Ec. If pole the ceramics under a. c. electric field of 3Ec, the electric field frequency had better not exceed f2. In general, the rare-earth Dy doping has significant effect on domain configuration and domain switching as well as the piezoelectricity.

Efficient Piezoelectric Energy Harvesting from a Discrete Hybrid Bismuth Bromide Ferroelectric Templated by Phosphonium Cation.

Bismuth containing hybrid molecular ferroelectrics are receiving tremendous attention in recent years owing to their stable and non-toxic composition. However, these perovskite-like structures are primarily limited to ammonium cations. Herein, we report a new phosphonium based discrete perovskite-like hybrid ferroelectric with a formula [Me(Ph)3 P]3 [Bi2 Br9 ] (MTPBB) and its mechanical energy harvesting capability. The Polarization-Electric field (P-E) measurements resulted in a well-defined ferroelectric hysteresis loop with a remnant polarization value of 2.1 μC cm-2 . Piezoresponse force microscopy experiments enabled visualization of the ferroelectric domain structure and evaluation of the piezoelectric strain coefficient (d33 ) for an MTPBB single crystal and thin film sample. Furthermore, flexible devices incorporating MTPBB in polydimethylsiloxane (PDMS) matrix at various concentrations were fabricated and explored for their mechanical energy harvesting properties. The champion device with 20 wt % of MTPBB in PDMS rendered a maximum peak-to-peak open-circuit voltage of 22.9 V and a maximum power density of 7 μW cm-2 at an optimal load of 4 MΩ. Moreover, the potential of MTPBB-based devices in low power electronics was demonstrated by storing the harvested energy in various electrolytic capacitors.

Characterization of Pb(Fe1/2Nb1/2)O3 ceramic as a potential candidate for photovoltaic and magnetoelectric applications

An impurity-free Pb(Fe1/2Nb1/2)O3 (PFN) ceramic was prepared using a conventional solid-state reaction method with precisely controlled sintering temperature. The PFN ceramic exhibits monoclinic symmetry and shows a dense morphology with equiaxed grains of about 1–2 μm. It exhibits a diffused phase transition at approximately 381 K. From the data of dielectric loss tangent and the imaginary parts of impedance and electrical modulus, a non-Debye type dielectric relaxation was investigated, and it was found that the short-range hopping of oxygen vacancies contributes to the dielectric relaxation and the relaxation time distribution is temperature independent. The PFN ceramic exhibits slim ferroelectric hysteresis loops and a linear magnetic hysteresis loop, indicating that the PFN ceramic is paramagnetic; the band gap is estimated to be 2.04 eV. Photoconductivity and photovoltaic responses with a nonzero open-circuit voltage and short-circuit photocurrent were detected. Moreover, magnetoconductivity was measured. This work implies that the PFN ceramic is a potential candidate for magnetoelectric and photovoltaic applications.

Dielectric and Piezoelectric Properties of Mn-Doped Bi(Mg1/2Ti1/2)O3-PbTiO3 Piezoelectric Single Crystals with MPB Composition

Mn-doped BMT-PT single crystals were grown using a flux method. The crystals were irregular and 4–10 mm in size. The EPMA and XRD results showed that the composition of the crystals was in the range of MPB. The room temperature dielectric permittivity εr and dielectric loss tanδ were 806 and 3.4% at 1 KHz. As the temperature increased, the rhombohedral phase did not first transform into the tetragonal phase, but transformed into the cubic phase directly. Owing to the Mn-doping, the ferroelectric hysteresis loops of the sample were quite narrow. The Curie temperature Tc, piezoelectric coefficient d33 and thickness electromechanical coupling factor kt of the single crystals along the <001> direction were 464 °C, 392 pC/N and 0.51, respectively. The piezoelectric properties are much better than the values of the ceramics and the undoped BMT-PT single crystals with a MPB composition.

Reduction of depolarization field effect on ferroelectric switching process in semiconductor–relaxor ferroelectric composite

Temperature-dependent dynamic ferroelectric hysteresis of semiconductor–relaxor ferroelectric (0–3) type composite {0.30(ZnO)–0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBTO)]} has been investigated using polarization–electric field (P–E) loops, current density–electric field (J–E) curves, and temperature-dependent dielectric permittivity. It is well known that the polarization reversal mechanism can be explained by the concept of ferroelectric domain switching kinetics, which depends strongly on the temperature. The present work ascribes the role of polar nanoregion induced thermal depolarization field on the temperature-dependent ferroelectric hysteresis loop along with polarization reversal mechanism. The present composite exhibits unique ferroelectric switching behavior above the thermal depolarization temperature (∼100 °C), which is observed in P–E and J–E loops. The depolarization field-induced pinched P–E loops of a BNBTO solid solution above Td (∼100 °C) have been significantly overcome by the incorporation of semiconductor (ZnO) particles, which extensively described the underlying mechanism in the present context. In addition, the temperature-dependent polarization reversal mechanism displays unique two-stage processes [low-T (<100 °C) and high-T (>100 °C)] for the minor loops (∼30 and 40 kV) and saturated loops (∼45 kV) as described by the electric field–temperature phase diagram. The present results may provide a distinct way to Bi0.5Na0.5TiO3-based solid solutions for high-temperature piezoelectric applications.

Pure PZT95/5 Ceramics and Its Phase Transition Behavior Under External Fields

Background: Compositionally modified Pb(Zr0.95Ti0.05)O3 (PZT 95/5) ferroelectric materials have been extensively investigated in past decades for many important applications. However, few study on pure PZT95/5 ceramics have been reported. Objective: Herein, pure PZT95/5 ceramics were successfully prepared, and their microstructure and phase transition behaviors under external fields were studied. Methods: The pure PZT95/5 ceramics were prepared by the conventional solid state reaction using a mixed oxide route. The microstructure and its properties under different external fields were measured. Results: The X-ray diffraction patterns indicated that the virgin pure PZT95/5 ceramics exhibit an orthorhombic antiferroelectric phase, which has also been evidenced by the superlattice reflections in the SAED pattern. While a rhombohedral ferroelectric symmetry crystal structure was observed in the poled samples suggesting that an electric field induced antiferroelectric to ferroelectric phase transition takes place. Pure PZT95/5 ceramics exhibit a quenched ferroelectric hysteresis loop with a remnant polarization of ~8μC/cm2 under 3.5kV/mm. Temperature dependence dielectric response indicated that the orthorhombic antiferroelectric to cubic paraelectric phase transition occurs at 225°C, corresponding to its Curie temperature. A shard depolarization behavior and dielectric anomalies were observed under ~240 MPa hydrostatic pressure. Conclusions: The depolarization mechanism of pure PZT95/5 ceramics under hydrostatic pressure is attributed to the hydrostatic pressure-induced FE-AFE phase transition. These results will offer fundamental insights into PZT95/5 ceramics for pulsed power supply applications.

A Combination of Calcination and the Spark Plasma Sintering Method in Multiferroic Ceramic Composite Technology: Effects of Process Temperature and Dwell Time.

This study reports a combined technological process that includes synthesis by the calcination powder route and sintering by the Spark Plasma Sintering (SPS) method for multiferroic ceramic composites in order to find the optimal sintering conditions. The effects of temperature on the SPS process and dwell time on the microstructure and dielectric properties of the PF composites were discussed. Research has shown that using the SPS method in the technological process of the multiferroic composites favors the correct densification of powders and allows for obtaining a fine-grained microstructure with good properties and electrophysical parameters in the composite material. The optimal set of parameters and properties is demonstrated by the sample obtained at the temperature of 900 °C for 3 min, i.e., resistivity (6.4 × 108 Ωm), values of the dielectric loss factor (0.016), permittivity at room temperature (753) and permittivity at the phase transition temperature (3290). Moreover, due to the high homogeneity of the microstructure, the strength of the material against electric breakdown increases (when examining the ferroelectric hysteresis loop, the application of a high electric field (3—3.5 kV/mm) is also possible at higher temperatures). In the case of the composite material tested, both the lower and higher temperatures as well as the shorter and longer dwell times (compared to the optimal SPS process conditions) did not contribute to the improvement of the microstructure or the set of usable parameters of the composite materials. The strength of the ceramic samples against electric breakdown has also diminished, while the phenomenon of leakage current increased.

Nanostructured BaTi1-xSnxO3 ferroelectric materials for electrocaloric applications and energy performance

Nanostructured BaTi1-xSnxO3 (x = 0, 0.05 & 0.075) were successfully synthesized using the modified Pechini processing method. The phase purity and symmetry were examined by X-ray diffraction and Raman spectroscopy. Tetragonal symmetry was obtained for BaTiO3 (BT) while orthorhombic symmetry for Sn doped BT. BT exhibits an up-shift of the Curie temperature towards high temperatures (TC = 139 °C). In contrast, a down-shift was recorded for Sn doped BT. Then, indirect electrocaloric (EC) adiabatic temperature change ΔT and the energy storage performances were determined based on ferroelectric hysteresis loops. Interestingly, large EC responsivity of ΔT/ΔE = 0.81 × 10−6 K m/V was obtained for the BT accompanied with a moderate stored energy of 23 mJ/cm3 but with a high energy efficiency of 67%. The incorporation of Sn in BT was found to broaden the EC responsivity and to improve the energy efficiency up to 90%, recorded for the 5% Sn doped BT.

Chemical control of polarization in thin strained films of a multiaxial ferroelectric: Phase diagrams and polarization rotation

The emergent behaviors in thin films of a multiaxial ferroelectric (FE) due to electrochemical coupling between the rotating polarization and surface ions are explored within the framework of the 2--4 Landau-Ginzburg-Devonshire (LGD) thermodynamic potential combined with the Stephenson-Highland (SH) approach. The combined LGD-SH approach allows us to describe the electrochemical switching and rotation of a polarization vector in a multiaxial ferroelectric film covered by surface ions with a charge density defined by the oxygen pressure. We calculate phase diagrams, analyze the dependence of polarization components on the applied voltage, and discuss the peculiarities of quasistatic ferroelectric, dielectric, and piezoelectric hysteresis loops in thin strained multiaxial ferroelectric films. The nonlinear surface screening by oxygen ions makes the diagrams very different from the known diagrams of, e.g., strained ${\mathrm{BaTiO}}_{3}$ films. Quite unexpectedly, we predict the appearance of ferroelectric reentrant phases. The obtained results point to the possibility to control the appearance and features of ferroelectric, dielectric, and piezoelectric hysteresis in multiaxial FE films covered with surface ions by varying their concentration via the partial oxygen pressure. The LGD-SH description of a multiaxial FE film can be further implemented within the Bayesian optimization framework, paving the way toward predictive materials optimization.

Nonvolatile modulation of luminescence in perovskite oxide thin films by ferroelectric gating.

Nonvolatile and giant modulation of luminescence can be realized by the ferroelectric gating effect in a Ga3+/Pr3+ co-doped BaTiO3 ultra-thin film epitaxially grown on a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 single-crystallized substrate. The change behavior of the emission intensity matches that of the ferroelectric polarization hysteresis loop with a giant enhancement of over 13 times with negative polarization orientation. The interaction of O2- at the O2p orbital in the valence band and Pr3+ with injected holes by the ferroelectric gating effect promotes the formation of excited state O-, Pr4+, or Pr3+q. This ferroelectric gating method can promote the development of controllable photo-, electroluminescent, and other optoelectronic devices for display, sensing, communication, and so on.