Switched Charge Density Research Articles

Optimization of switching charge and recoverable energy density mediated by structural transformation in Sr-substituted BaNiO3 perovskites.

Because of their distinctive characteristics, ferroelectric perovskites are considered among the most potent and auspicious candidates for energy storage and pulsed power devices. But their energy storage properties and switching capabilities need to be further enhanced which can be done by substitutions of appropriate cations. Hence, a series of lead-free Ba1-xSrxNiO3 (x = 0.00, 0.33, 0.67, and 1.00) ceramics was fabricated using a sol-gel auto combustion technique. Rietveld's refinement of X-ray diffraction plots verified the complete development of the required hexagonal perovskite structure. Scanning electron microscopy images revealed a gradual increase in average grain sizes and agglomeration with the increase in Sr-content. Moreover, the existence of all the constituent elements exactly in proportion to their stoichiometric ratios was verified by energy dispersive X-ray spectroscopy. The characteristic parameters of ferroelectric materials such as ferroelectric response, electrical conductivity, and switching charge density were also determined. The P-E loops indicated that with the increase in Sr-content, the coercive field, remanent polarization, and maximum polarization all decreased gradually, but the recoverable energy density (Wrec) increased as the loops became slimmer. The maximum value of Wrec was found in the Ba0.33Sr0.67NiO3 sample. Moreover, SrNiO3 exhibited minimum energy loss with the highest efficiency of ∼47.21%. The existence of a current barrier in all the samples was proved from the low leakage current values (∼10-7 A). In addition, the pure SrNiO3 showed a low electrical conductivity and minimum value of switching charge density. All these findings make SrNiO3 a promising candidate for fast switching and energy storage applications.

Multiferroic properties of Ba2+-Ti4+ co-doped YFeO3 ceramics

The search for multiferroic materials with ferroelectric and ferromagnetic properties at room temperature continues to be driven by the prospect of new devices. In this paper, Ba2+-Ti4+ co-doped Y1-x(Ba0.5Ti0.5)xFeO3 were prepared by a traditional solid-state reaction method. The ferroelectricity and ferromagnetism of the co-doped ceramics have been enhanced simultaneously with the maximum polarization of 0.48 μC/cm2 and the maximum magnetization of 3.25 emu/g, the switched charge density (0.26 μC/cm2) measured by PUND tests indicating the intrinsic and switchable remanent polarization. The increase of Fe2+ content (increased to 28 % with the increase of doping content) caused by Ba2+-Ti4+ co-doping destroys the antiferromagnetic ground state, and the doping strategy enlarges the tilt angle of oxygen octahedron from 144.93° to 148.63°. The magnetic domain switches caused by the external electric field were directly observed by magnetic force microscopy, indicating the modulation of magnetic domain by polarization at room temperature. This work may provide useful information for the structural design and performance improvement of multiferroic materials.

Optimization of magnetoelectric coupling in BiFeO3-BaTiO3-MnFe2O4 tri-phase composites for ultra-sensitive devices

Multiferroic materials with coupled electric and magnetic orderings have astonished the scientific community by exhibiting magnetoelectric (ME) coupling, viable for multistate memory devices. Facile synthesis of multiferroic composites have further triggered these delightful attributes. Here we present a series of tri-phase composites of the form; (1–x)(0.7BiFeO3 + 0.3BaTiO3) + xMnFe2O4, synthesized by a facile two-step method. The phase-pure synthesis was confirmed using X-ray diffraction. For energy storage capability, a composition with x = 0.02, reveals the recoverable energy density of ∼0.22 mJ/cm3 followed by the highest efficiency of 64.02%, making such composition favourable for energy storage perspectives at minute inclusion of the spinel phase. The characteristic I-V curves were used to explain the leakage current of BiFeO3 (BFO). The positive up and negative down (PUND) sequence demonstrates the significant variation in switching charge density. The gradual increase in grain size resulted in a lowering of the coercivity values up to 301 Oe at x = 0.10 having 6.31 emu/g as saturation magnetization (MS) value along with MR/MS ratio of 0.33. The linear response shown by ME coupling at x = 0.06 along with the afore mentioned attributes make this composition a potential candidate for ultra-sensitive magnetoelectric devices.

Gateway toward efficient and miniaturized A 2 B 2O7-type fluorite structure-based energy storage devices.

Defect fluorite structure with A 2 B 2O7 composition exhibits an intense potential for utilization in modern smart electrical devices. Efficient energy storage with low loss factors like leakage current makes them a prominent candidate for energy storage applications. Here we report a series of the form Nd2-2x La2x Ce2O7 with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, synthesized via a sol-gel auto-combustion route. The fluorite structure of Nd2Ce2O7 is slightly expanded with the incorporation of La without any phase transformation. A gradual replacement of Nd with La causes a decrease in grain size, which increases the surface energy and thus leads to grain agglomeration. The formation of exact composition without any impurity element is confirmed by energy-dispersive X-ray spectra. The polarization versus electric field loops, energy storage efficiency, leakage current, switching charge density, and normalized capacitance, which are considered key features of any ferroelectric material, are comprehensively examined. The highest energy storage efficiency, low leakage current, small switching charge density, and large value of normalized capacitance are observed for pure Nd2Ce2O7. This reveals the enormous potential of the fluorite family for efficient energy storage devices. The temperature-dependent magnetic analysis exhibited very low transition temperatures throughout the series.

Effectively coupled BiFeO3-MnFe2O4-Cr2O3 tri-phase multiferroic composites for efficient energy storage and fast switching

Owing to several unique features, multiferroic materials and their composites are gaining significance in microelectronic and spintronic based devices. In particular, the magnetic and electric orders of these materials can effectively be tuned and their reciprocal control is also feasible. In this context, this work presents a series of 0.8[(1–x)BiFeO3 + xMnFe2O4] + 0.2Cr2O3 nanocomposites, synthesized by sol–gel auto-combustion and solid state ball milling routes. The diffraction analysis confirmed the required crystalline phases. The precise crystallite size was calculated using Scherrer's equation and a compared with the sizes obtained with the Williamson-Hall plots. Energy dispersive X-ray spectroscopy confirmed the presence of all the required stoichiometric elements in agreement with empirical formulae. A gradual increase in the average grain size was observed using microscopic images. The rising gap between recovered energy and energy loss, noted at optimized spinel phase contents, make these composites potential choice for the efficient energy storage devices. At 'x = 0.4,' the greatest value of energy density efficiency ∼ 68.4%, was recorded. The I-V analysis indicated that all of the samples had a current barrier. The switching charge density was enhanced with the substitution of spinel phase, confirmed from PUND data. Magnetic analysis revealed that saturation magnetization of in the composite series increased from 0.85 to 55.5 emu/g and coercivity decreased from 170 to 90 Oe, whereas the remanent magnetization increased from 0.15 to 4.5 emu/g. Such findings demonstrated the applications of prepared samples in a variety of ways including energy and data storage devices.

Strain induced electromagnetic coupling in tri-phase multiferroic composites 0.8[(1-x)Fe2O3–xPbZrO3]+0.2Cr2O3 for multistate devices

Multiferroic composites are highly desirable for next-generation multifunctional smart devices because of their low power consumption, fast data processing, and nonvolatile nature in memory devices. Here we synthesized a series of tri-phase composite of Fe2O3, PbZrO3, and Cr2O3 with general formula 0.8[(1-x)Fe2O3–xPbZrO3]+0.2Cr2O3 (x = 0.0, 0.33, 0.66 and 1.0) via a chemical approach. Individual oxides are synthesized by the sol-gel auto-combustion method and the solid-state route is used to mix them. Through structural analysis, the formation of tri-phase composites is confirmed by the presence of peaks belonging to each phase. The morphological study suggested that the composites have a homogeneous distribution of grain size over the surface with small voids. To investigate the ferroelectric nature of these composites the saturation polarization, remanent polarization, and coercivity are calculated from their P-E loops. Using these values, the switching charge density and recoverable energy density are evaluated which highlighted the importance of these composites for fast switching and energy storage devices. The response of variation in polarization by the magnetic field is mapped by magneto-electric coupling measurement. Our results show that these tri-phase composites with ferroelectric and magnetoelectric response are potential candidates for high-density data storage and ME multifunctional devices.

Efficient energy storage and fast switching capabilities in Nd-substituted La2Sn2O7 pyrochlores

Pyrochlore materials show intensive potential for various everyday applications owing to their highly stable structure with tunable lattice parameters. Energy storage tunability and switching capabilities of these materials can further be improved using suitable cationic substitutions. In this context, we report a series of Nd-substituted lanthanum stannate (La2−xNdxSn2O7) pyrochlores, prepared using sol-gel auto-combustion method. It has been observed that Nd-substitution finely tuned the lattice parameters of parent compound without compromising its cubic phase stability. The gradual replacement of La with Nd resulted in well crystalline grains, adopting diamond and cubic like shapes. Ferroelectric nature, electrical conductivity, switching charge density and normalized capacitance, which are among the key features of a ferroelectric material, were also analyzed. The increasing difference between saturation and remanent polarizations, especially when x ≥ 1.2, make them a potential candidate for energy storage devices. The maximum value of energy density efficiency i.e. more than 60% was observed for pure Nd2Sn2O7. In addition, low switching charge density makes them prominent for fast switching applications. Magnetic response revealed their superparamagnetic behavior with small remanence and low coercivity (~30 Oe), which exposed their potential for biomedical applications provided its particle size is controlled.

Effect of domain switching contribution on polarization current, leakage current and switching charge density studied by PUND method in (Ba1−x,Cax)TiO3 ceramics

The present study illustrates the effect of domain switching on polarization current and leakage current in (Ba1−xCax)TiO3 (0 ≤ x ≤ 0.4) lead-free ceramics prepared by sol-gel method. The influence of Ca2+ concentration on the structural, microstructure and dielectric properties of BaTiO3 (BT) was investigated. The study shows that domain switching has a significant effect on polarization current and switching leakage current behavior. Un-switching leakage current was observed to be lower than the switching leakage current in whole range of electric field due to restrict the space charges contribution in the absent of domain switching effect. The highest polarization current and lowest leakage current were achieved in the composition x = 0.2. Effect of frequency into polarization current has been introduced, where the current peak increased and shifted to higher electric field by increasing the applied frequency due to the high rate change of electric field corresponding domain switching rate. The difference between remnant polarization estimated by P-E loop and Positive Up Negative Down (PUND) methods has been highlighted. The results show that the remnant polarization appraised by PUND method is lower than the value estimated by P-E loop due to absence of the leakage current contribution.

Study of (1−x) BaTiO3–x Ni0.5Zn0.5Fe2O4 (x = 5, 10 and 15%) magneto-electric ceramic composites

Structural, magnetic, ferroelectric and magneto-electric studies of BaTiO3 (BTO)–x Ni0.5Zn0.5Fe2O4 (NZFO) ceramic composites are reported. The fraction of NZFO, i.e., ferrite phase is varied from 0% to 15%. The prepared ceramics are studied using X-ray diffraction, Raman spectroscopy, magnetization and ferroelectric measurements. Using X-ray diffraction and Raman spectroscopy measurements, the bi-phase formation of the composites is confirmed. From the high temperature magnetization measurements, anomaly in the magnetization is observed at ferroelectric transition temperature of BTO phase indicating the presence of magneto-electric coupling. Positive Up Negative Down (PUND) measurements are employed to capture the true ferroelectric polarization, i.e., true switched charge density (QS). The strength of ME coupling is studied by measuring the QS before and after magnetic poling and it is observed that for x = 10% composition the ME coupling is maximum for the studied compositions.

Low Voltage Operation of Ferroelectric Capacitors using Sr-Deficient and Praseodymium-Substituted Strontium Bismuth Tantalate Ultra Thin Films

Sr-deficient and praseodymium-substituted SrBi2Ta2O9 (SPrBT) ultra thin films were formed on a Pt/Ti/SiO2/Si structure using a sol-gel method, in which the remanent polarization was saturated at an applied voltage lower than 1 V. The remanent polarization and coercive voltage values of a 61-nm-thick SPrBT film annealed at 800°C were 3.4 μC/cm2 and 0.16 V (an electric field of approximately 26 kV/cm), respectively. The switching charge density (Q SW ) value at an applied voltage of 2 V was 6.8 μ C/cm2, and the 90%-reduction of the Q SW value was obtained at an applied voltage of 0.9 V.

Effect of thickness and upper electrode diameter on polarization switching and electron emission of Pb(Zr0.8Ti0.2)O3 ferroelectric cathode

To investigate the structural effect on the ferroelectric electron emission, the electric field distribution in a two-dimensional structure was calculated as a function of thickness and upper electrode diameter, and the switching charge density and emission charge were measured simultaneously. The simulation results of the electric field distribution showed that an asymmetric electrode structure caused a stray field on the bare surface of the ferroelectric cathode near the edge of upper electrode. The distance of the stray field from the electrode edge increased with increasing ferroelectric thickness, but it did not depend on the upper electrode diameter. The switching charge density increased more on the cathode with thicker ferroelectric and smaller upper electrode diameter. This was attributed to the difference of field distribution on the bare ferroelectric surface near the electrode edge. The expanded stray field for the thicker ferroelectric cathode enhanced polarization switching near the electrode edge. As a result, with increasing ferroelectric thickness, the emission charge increased and the threshold field decreased. However, there was no apparent difference between the emission charges from the different upper electrode diameters.

Ferroelectric properties of epitaxial barium titanate thin film capacitors on silicon substrate

A heteroepitaxial BaTiO3 film with a thickness of 65 nm was prepared on SrRuO3/Pt/TiAlN/Si. The Ti0.91Al0.09N film was grown on Si substrate by DC sputtering in Ar/N2 ambient at 700°C. The BaTiO3, SrRuO3 and Pt films were deposited by radio-frequency magnetron sputtering at substrate temperatures ranging from 450°C to 600°C. The BaTiO3 film has a c-axis 1.6% longer (0.410 nm) than that of bulk, due to lattice misfit between SrRuO3 and BiTiO3. When positive and negative voltage pulses with an amplitude of 5 V were applied, a switching charge density, Q sw, of 40 μC/cm2 was obtained. No fatigue was observed after 1011 cycles of polarization switching even when an amplitude of 7 V was applied. Remanence of polarization for 4 hours was confirmed in a retention test. These results indicate that the heteroepitaxial BaTiO3 film capacitors on Si substrates can be used for ferroelectric nonvolatile memory applications.

Fatigue Behavior in Lead-Zirconate-Titanate Thin-Film Capacitors Prepared by Pulsed Laser Ablation on Ni-Alloy Electrodes

Ferroelectric lead-zirconate-titanate (Pb(Zr0.52Ti0.48)O3: PZT) thin-film capacitors were fabricated by pulsed laser ablation using Ni-alloy electrodes on oxidized (100) silicon. Polarization fatigue after a large number of switchings was investigated with a variety of frequencies. The frequencies for acceleration of fatigue and for measurement of the switched charge density Q sw were varied simultaneously or independently. The fatigue test revealed that the increase in the frequency both for acceleration and measurement of switching pulse increases the life of polarization reversal while it decreases Q sw. At 50 kHz, Q sw keeps the initial value even after switching above 1010 cycles. The measurement frequency dependence of Q sw suggests that a homogeneous fatigue takes place irrespective of fast and slow domains and additional layers of a low dielectric constant are probably formed in the ferroelectric-metal interface.

Ferroelectric properties of plzt thin films prepared by mocvd

Abstract Lanthanum-modified lead zirconate titanate (PLZT) thin films have been grown on Pt/SiO2/Si substrate at 650[ddot]C by metalorganic chemical vapor deposition. The relative dielectric constant increased as the La content was increased up to about 5 atomic percent (at%). The remanent polarization and coercive field decreased from 30 to 20 μC/cm2 and from 53 to 30 kV/cm, respectively, with increasing La content in the range of 0–13 at%. The leakage current of PLZT film was 3 × 10−9 A/cm2 at an applied voltage of 3 V. The degradation of switched charge density of PLZT film was not observed even at 2 × 1011 cycles.

Electrical Properties of PZT Prepared by Pulsed Laser Ablation on Various Electrodes

ABSTRACTThe effect of various electrodes on the ferroelectric properties of lead-zirconate-titanate (Pb(Zr0.52Ti0.48)O3 PZT) films through the film structure is presented. All the PZT films were deposited by pulsed laser ablation (PLA) using an ArF excimer laser. For electrode materials, YBa2Cu3O7 (YBCO) and Ni-alloy were deposited by pulsed laser ablation and sputtering, respectively. As a result various kinds of PZT films with various film structures were obtained. These experiments revealed that there is no simple correlation between the film structure and the fatigue resistance. The fatigue resistance is, however, found to be improved primarily by decreasing the switched-charge density, although the correlation shows some ambiguity. This suggests that the large polarization reversal accelerates the fatigue but there remained the possibility that the fatigue resistance is improved by the optimization of the film structure and film-substrate interface.

Phase slippage, nonadiabatic effect, and dynamics of a source of traveling waves.

Experimental studies of the source dynamics of counterpropagating waves in a convecting binary fluid are presented. The source motion is controlled by side heating. There exists a locking band inside which the source is pinned by the underlying roll structure. Outside this band the source commences to move abruptly by steps of half a wavelength. A distortion of the phase field and the resulting nonlinear flow are essential ingredients responsible for the abrupt transition to the sliding state. Strong similarity to switching charge density waves dynamics is discussed.

Preparation and Characterization of Pb(ZrxTi1-x)O3 Thin Films by Reactive Sputtering Using an Alloy Target

Pb(Zrx, Ti1-x)O3 (PZT) thin films were deposited on Pt/SiO2/Si substrates by rf-magnetron sputtering using an alloy target consisting of Zr-Ti alloy and a Pb metal. When an alloy target was used in reactive sputtering, no change was observed in the Zr/Ti ratio of the films for up to 300 h for target uses. The (111)-oriented PZT films were successfully grown at substrate temperatures of 605-620°C. The coercive fields (Ec) and remanent polarizations (Pr) of the films with only the perovskite phase were in the range of 70-72 kV/cm and 20-22 µC/cm2, respectively. In fatigue behavior, switched charge density started to drop at 108 cycles.

Time-domain study of low-dimensional chaos in the switching charge-density-wave conductor NbSe3.

We study the dynamics of switching charge-density waves (CDWs) in the presence of combined dc and ac electric fields. Analysis of the time series provides Lyapunov exponents, and an estimate for the number of active degrees of freedom. The dynamics are both low dimensional and chaotic. The principal nonlinearity which gives rise to the chaos in switching CDWs is shown to be the hysteresis in the depinning transition, rather than the interaction between two frequencies.

Switching characteristics of multi-ion-beam reactive sputter deposited Pb(Zr,Ti)O3 thin films

The switching of the multi-ion-beam reactive sputter deposited Pb(Zr0.5,Ti0.5)O3 thin films has been characterized by using several parameters such as switching time (ts), switched charge density (Qs), nonswitched charge density (Qns), and activation field (α). Comparison was made between films grown with and without low-energy oxygen ion bombardment. It was found that while there is not much difference in ts between the two kinds of films, the bombarded films show higher Qs/Qns, lower ts/Qs, and lower α. These results are consistent with previous results on the remanent polarization (Pr) and coercive field (Ec) and indicate that the bombardment has induced changes towards facilitating the domain reversal in the films.

Nonlinear dynamics of a breakable chain at threshold: Large-N results.

We investigate the behavior of a chain of N nonlinear oscillators, in a model originally invoked to describe depinning of switching charge-density waves. The dynamics is dominated by the coexistence of a large number of attractors, one of which\char21{}the minimally stable state\char21{}plays a central role. At threshold, very broad depinning-time distributions occur for long chains. Physically, these long times reflect very slow motion punctuated by rapid but localized motion of the chain.