Polarization Loops Research Articles

Preparation and ferroelectric properties of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) filled with graphene-nanoplatelets film composites

The poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP composite films with addition graphene-nanoplatelets (GPN) was prepared by using the tape casting solution method. The obtained composite films were stretched with help from thermal stretching machine at 80 °C with 5 mm/min rate. Dielectric constant and hysteresis loop (PE-loop) between the stretching and non-stretching films at different fillers percentage were compared in this study. Dielectric constant was investigated by the LCR meter. The PE-loop was measured by the ferroelectric polarization loop test system. The experimental results showed that the dielectric constant of all samples increases with increasing fillers content, regardless of frequency. The dielectric constant of stretching composite films was higher than non-stretching composite films. In addition, the PE-loop shapes of the stretching films have slimmer than the non-stretching films regardless of filler content. However, the PE-loop produced the shape to be bigger loop with increasing filler content. The energy efficiency of obtained PVDF-HFP composite films will be discussed on their dielectric constant, dielectric loss, AC conductivity, and polarization performances for electric–capacitor materials applications.

Structural, dielectric and electrical characteristics of yttrium modified 0.7BiFeO3-0.3PbTiO3

Some yttrium modified BiFeO3–PbTiO3 (BYFO-PT) compounds have been fabricated using a standard ceramic technology (solid-state route). The structural analysis from X-ray diffraction (XRD) data ensures the formation of the rhombohedral phase of the compounds. The prepared materials have major bismuth ferrite (70%) and lead titanate (30%) with few impurity phases. The materials are found to have a high dielectric constant and low tangent loss. The relaxation mechanism is identified from the peaks appearing in impedance and modulus curves. The materials show a negative temperature coefficient of resistance (NTCR) semiconductor type behavior in the temperature range of 250 °C–400 °C. In addition, grain and grain boundary effects are observed through the Nyquist plots. The activation energy (Ea) of the compounds is calculated from the slope of inverse temperature versus AC conductivity at the high-temperature range. The ferroelectric nature of the compounds is confirmed by electric field dependent polarization (PE-hysteresis) loops.

Understanding the effects of electric-field-induced phase transition and polarization loop behavior on the energy storage performance of antiferroelectric PbZrO3 thin films

Antiferroelectric PbZrO3 (PZO) thin-films were fabricated by pulsed laser deposition (PLD) and sol-gel techniques to investigate the effect of antiferroelectric-ferroelectric (AFE-FE) phase transition on the energy storage performance. The (100)-oriented PLD thin-films have a square-double polarization-electric field (P-E) hysteresis loop with a sharp-phase transition and the (111)-oriented sol-gel thin-films have a slanted P-E loop with a diffused-phase transition. The difference in the phase transition fields between PLD and sol-gel thin-films could be attributed to their difference in crystalline orientations. In this case, the antipolar AFE phase is along the [110]-direction of the original tetragonal-cell under zero electric-field, while the antipolar AFE phase switches into the polar FE phase under a strong enough electric-field and the tetragonal-cell becomes rhombohedral with the polar direction of [111]. Due to the larger maximum polarization and slimmer P-E loop, the higher recoverable energy-storage (Ureco) of 19.4 J/cm3 and larger energy-efficiency (η) of 70.8%, are achieved in sol-gel thin-films. More importantly, this film shows excellent charge-discharge cycling endurance of both Ureco and η values after 1010 cycles and good thermal-stability under a wide operating temperature. From the viewpoint of applications, the sol-gel method is considered to be a promising approach towards producing low-cost PZO thin-films for high-efficiency energy-storage devices over a broad temperature range.

On the Importance of the Work Function and Electron Carrier Density of Oxide Electrodes for the Functional Properties of Ferroelectric Capacitors

It is important to understand the effect of the interfaces between the oxide electrode layers and the ferroelectric layer on the polarization response for optimizing the device performance of all‐oxide ferroelectric devices. Herein, the effects of the oxide La0.07Ba0.93SnO3 (LBSO) as an electrode material in an PbZr0.52Ti0.48O3 (PZT) ferroelectric capacitor are compared with those of the more commonly used SrRuO3 (SRO) electrode. SRO (top)/PZT/SRO (bottom), SRO/PZT/LBSO, and SRO/PZT/2 nm SRO/LBSO devices are fabricated. Only marginal differences in crystalline properties, determined by X‐ray diffraction and scanning transmission electron microscopy, are found. High‐quality polarization loops are obtained, but with a much larger coercive field for the SRO/PZT/LBSO device. In contrast to the SRO/PZT/SRO device, the polarization decreases strongly with increasing field cycling. This fatigue problem can be remedied by inserting a 2 nm SRO layer between PZT and LBSO. It is argued that strongly increased charge injection into the PZT occurs at the bottom interface, because of the low PZT/LBSO interfacial barrier and the much lower carrier density in LBSO, as compared with that in SRO, causing a low dielectric constant, depleted layer in LBSO. The charge injection creates a trapped space charge in the PZT, causing the difference in fatigue behavior.

Design strategies for improvement in nonvolatile memory characteristics of metal-ferroelectric-metal-insulator-semiconductor capacitors using ferroelectric Hf0.5Zr0.5O2 thin films

The effects of top electrode and thickness control of ferroelectric HfxZr1−xO2 (HZO) film on the memory device characteristics were investigated for metal-ferroelectric-metal-insulator-semiconductor (MFMIS) capacitors. It was suggested from capacitance-voltage analysis for the MFM and MFMIS capacitors that the Al top electrode increased leakage current components and caused memory retention degradation owing to the formation of intermediate transistion layer at interfaces with HZO. Alternatively, the choice of Pt top electrode was appropriate to guarantee sound device operations without any reaction at interfaces. When the HZO thickness increased from 20 to 30 nm, the maximum memory window supported by ferroelectric field-effect increased from 2.6 to 3.1 V at an area ratio (MIS:MFM) of 60. Load-line and operating-point analysis show that polarization loops close to more saturated polarizations can be exploited for the memory operations of MFMIS capacitors using thicker HZO films. As a result, for the MFMIS capactior using 30 nm-thick HZO, the capacitance loss at on-state was only 8.7% after a lapse of retention time for 104 s. Choice of top electrode and control of HZO thickness were found to be important design parameters for highly-functional ferroelectric transistors using MFMIS gate-stack structures.

Evidence of magneto-electric coupling and electrical study of CFO modified BNT/BT composites

(1-x)(0.93Bi0.5Na0.5TiO3/0.07BaTiO3)-xCoFe2O4 ((1-x)BNT/BT-xCFO, where x = 0.1, 0.2, 0.3, 0.4 and 0.5) composite samples were synthesized by microwave assisted solid state reaction route and sintered at 1050 °C. X-ray diffraction study showed the presence of ferroelectric/ferromagnetic (FE/FM) phases without any peak of secondary phase. This was further confirmed by SEM study showing the presence of both FE/FM grains distinctly. Frequency dependent dielectric study showed maximum dielectric constant ("r) for the composite sample with x = 0.4. Polarization versus electric field (P-E) loop study revealed that maximum remnant polarization (2Pr = 1.75 μC/cm2) was found also for the 0.6BNT/BT-0.4CFO sample. Remnant magnetization (Mr) of the composite sample with x = 0.4 was found to be ∼7.81 emu/g. Magnetodielectric (MD) study of the 0.6BNT/BT-0.4CFO composite sample showed decrease in "r with the application of magnetic field and a MD effect of ∼2.4% (at 10 kHz) was found. Low leakage current value (∼10−4 A) was obtained in the 0.6BNT/BT- 0.4CFO composite sample. Change in piezoresponse force microscopy contrast after poling indicated on the changes in polarization of the ferroelectric domains. Reduction in Mr, observed in magnetic force microscopy contrast gave a clear evidence of presence of electric field induced magneto-electric (ME) coupling in the 0.6BNT/BT-0.4CFO composite sample.

Optical and functional properties of hydrothermally synthesized tetragonal Ba0.4Cu0.6−xLaxTiO3 (x = 0.2–0.6) nanoparticles

Ba0.4Cu0.6−xLaxTiO3 (x = 0.2, 0.4 & 0.6) (BCLT) nanoparticles were prepared by hydrothermal method. The x-ray diffraction (XRD) pattern established the existence of tetragonal phases. The nanospheres were observed in the surface morphology of present materials using the transmission electron microscopy (TEM). The optical properties were investigated to confirm the presence of metal oxide bonds as well as the optical band-gap energy of BCLT nanoparticles. The dielectric and impedance parameters were studied as a function of frequency and composition. The Cole-Cole plots were drawn to understand the microstructure and electrical conduction mechanism. In addition, the ferroelectric nature was carried out with the help of polarization versus electric field (P-E) loop tracer.

Voltage-driven strain-induced coexistence of both volatile and non-volatile interfacial magnetoelectric behaviors in LSMO/PMN-PT (0 0 1)

We report on the inhomogeneous electric field response of the magnetization in a La1−xSrxMnO3 (LSMO) film on a ferroelectric [Pb(Mg1/2Nb2/3)O3]1−x-[PbTiO3]x (PMN-PT) substrate. X-ray diffraction patterns of the LSMO film confirm successful epitaxial growth of LSMO along the [0 0 1] orientation of PMN-PT, where a sudden lattice relaxation in the LSMO film occurs due to a large lattice mismatch. The LSMO film exhibits magnetic anisotropy that lies in-plane and isotropic in all directions of the plane with a Curie temperature of 345 K. The polarization versus electric field (P–E) loop shows that a sharp switching of electric dipoles occurs and the switching field decreases with decreasing maximum applied electric field. The coexistence of hysteresis-like (non-volatile) and butterfly-like (volatile) behavior of the voltage induced Kerr signal is observed. We consider that 109° switching of the ferroelectric domains is responsible for the rotation of magnetic easy axis that results in the hysteresis like behavior while 71° and 180° switching of the ferroelectric polarization has no effect on the magnetic anisotropy, leading to the butterfly-like behavior.

Rotation induced charged pion condensation in a strong magnetic field: A Nambu–Jona-Lasino model study

We investigate the possibility of charged pion condensation in the presence of parallel rotation and magnetic field within the Nambu--Jona-Lasinio model with quarks as the fundamental degrees of freedom. Previous study based on non-interacting Klein-Gordon theory for pions showed that the charged pions will undergo Bose-Einstein condensation under this circumstance [Y. Liu and I. Zahed, Phys. Rev. Lett. ${\bf 120}$, 032001 (2018)]. In this work, we take into account the internal quark structures of charged pions self-consistently through quark polarization loops in an interacting theory, i.e., the Nambu--Jona-Lasino model. The stability of the system is explored against the formation of a nonzero expectation value of the composite charged pion field $\bar{u}i\gamma_5d$. We find that two competing effects are induced by the rotation: the isospin enhancement which favors charged pion condensation and the spin breaking which disfavors the condensation. For a strong magnetic field ($\sqrt{eB}\sim1{\rm GeV}$) and system size of a few fermi, the isospin enhancement effect is stronger than the spin breaking one, and the charged pion condensation becomes energetically favored beyond a critical angular velocity of a few MeV.

Dielectric dispersion in CoFe2O4/PVDF nanocomposites influenced by ceramic contents and thermal mediation

Characteristics like high dielectric constants, ferroelectric and coupled magnetic behaviour when combined in multiferroic materials become quite essential for use in numerous applications including multi-functional devices and also as multi-layer ceramic capacitors. In this context, ceramic polymer nanocomposites of CoFe2O4/polyvilylidene difluoride (CFO/PVDF) are prepared in this work. Energy dispersive X-ray spectra of the samples confirmed the presence of elements in the exact stoichiometric ratio. A field emission scanning electron microscope revealed the minute details of the morphological features of the composite films. In the frequency range of 20 Hz to 20 MHz, as frequency is increased, the dielectric constant (real and imaginary) and tangent loss show a decrease but with the increase in temperature and CFO concentration, the dielectric features show an increase. Electro active regions, resistance and relaxation frequencies of the samples have been explained using complex impedance spectroscopy. As frequency and temperature is increased, the conductivity increases as a result, due to an increase in concentration of CFO nanoparticles. The electric field induced polarization studied by precision ferroelectric tester shows a decreasing trend from a maximum value as some of the samples can show conductivity because polarization versus electric field (P–E) loop is elliptical shaped and these properties are of tremendous value for industrial and commercial applications.

Ferroelectric and Multiferroic Properties of Single-Phase Yb2NiMnO6 Double-Perovskites

Here we present the potential for single-phase Yb2NiMnO6 as a multiferroic 2D material with coupled ferroelectric/magnetic orders synthesized via solid-state reaction. Realistically large room- to elevated-temperature stable switching polarization reversal loops confirm the elevated temperature dense data bit storage material. Temperature-stable ferroelectricity and fine polarization recorded at room temperature and read at 200°C confirm elevated temperature dense data storage. The physics behind the coexistence of coupled orders is the focus of this work. Realistically large ferroelectric polarization loops produced at ±400 kV/cm confirm saturation polarization (PS) at around 20 μC/cm2. Microstructural and compositional analysis reveals that the ferromagnetic signature is generated from single-phase Yb2NiMnO6 with a confidence level of 99.95%. Rietveld refined x-ray diffraction reveals that Yb2NiMnO6 is a single-phase material displaying a GdFeO3-type orthorhombic structure with distorted (Ni/Mn)O6 (pnma; a = 5.5519 Ǻ; b = 5.1851 Ǻ; c = 7.4396 Ǻ; V = 214.18 Ǻ3). X-ray photoelectron spectroscopy confirms that Yb2NiMnO6 constituting the Mn2P3/2 core level appears at ∼642.2 eV and an Ni2P3/2 peak appears at ∼855.3 eV, displaying +4 and +2 valence states. Frequency dispersion and scaling behaviour in dielectric (e′) and dielectric loss (tanσ) indicate that the relaxation mechanism is independent of temperature. The σDC versus 1/T slope confirms that the hopping mechanism is responsible for charge carrier transport. The complex impedance reveals that the relaxation/conduction is the bulk effect arising from the semiconductor grains displaying grain resistance and capacitance with respect to temperature (113–363 K) and frequency (1–1 × 107 Hz). We have correlated and presented the effect of the microstructure on the electrical properties using an equivalent circuit (RgQg) (RgbQgb) (RcQc) at low temperature and changing to (RgbQgb) (RcQc) on high temperature. MS, HC and MR extracted from the ferromagnetic hysteresis loop are 11.75 emu/g, 180 Oe and 4.15 emu/g at room temperature (300 K). The zero-field-cooled and field-cooled magnetization (ZFC–FC) curve confirms the ferromagnetic nature. From these results, we show that Yb2NiMnO6 is multiferroic, with potential for application in four-state logic memory, ferroelectric random access memory and ferroelectric/magnetic sensors.

Deformation induced pseudomagnetic fields in complex carbon architectures

We show that the physics of deformation in $\alpha$-, $\beta$-, and $6,6,12$-graphyne is, despite their significantly more complex lattice structures, remarkably close to that of graphene, with inhomogeneously strained graphyne described at low energies by an emergent Dirac-Weyl equation augmented by strain induced electric and pseudo-magnetic fields. To show this we develop two continuum theories of deformation in these materials: one that describes the low energy degrees of freedom of the conical intersection, and is spinor valued as in graphene, and one describing the full sub-lattice space. The spinor valued continuum theory agrees very well with the full continuum theory at low energies, showing that the remarkable physics of deformation in graphene generalizes to these more complex carbon architectures. In particular, we find that deformation induced pseudospin polarization and valley current loops, key phenomena in the deformation physics of graphene, both have their counterpart in these more complex carbon materials.

New lead-free piezoelectric thin film fabricated using metal-oxide nanosheets at low temperature

A new lead-free piezoelectric film consisting of Sr2NaNb4O13− (SNNO−) and TiNbO5− (TNO−) nanosheets was fabricated via electrophoresis. SNNO and TNO films display paraelectric polarization versus electric field (P-E) loops. However, a new film composed of a mix of SNNO− and TNO− (S/T) nanosheets displayed a ferroelectric P-E hysteresis loop with large maximum polarization (18.7 μC/cm2), remnant polarization (7.7 μC/cm2), and a coercive electric field (86 kV/cm). The interfaces formed between the SNNO and TNO layers induced ferroelectric properties in the S/T film through the occurrence of polar distortion and octahedral tilting in the film. Ferroelectric properties were also observed in piezoelectric force microscopy images of the S/T film, which showed 90° domains after the removal of the applied electric field. The dielectric constant of the S/T film was 70, which is higher than those of SNNO and TNO films, indicating that the S/T film is a ferroelectric material. The piezoelectric strain constant of the S/T film was 156 p.m./V and promising insulating properties were observed therein. The growth temperature of the S/T film was low (300 °C), suggesting that the S/T film can be used for flexible electronic devices.

Neutral meson properties in hot and magnetized quark matter

In this work we evaluate the π0 pole-mass in the RPA approximation at finite magnetic field and temperature in the NJL SU(2) model. To this end, we employ an alternative version of the Magnetic Field Independent Regularization based on the Riemann-Hurwitz zeta function. To employ this formalism, we present a set of equations applied to the gap equation and pseudo-scalar polarization loop at the mean field approximation and random phase approximation.

Experimental evidence of breakdown strength and its effect on energy-storage performance in normal and relaxor ferroelectric films

Normal-ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin-films are deposited on SrRuO3-covered SrTiO3/Si substrates. An ultrahigh recoverable energy-storage density (Ureco) of 68.2 J/cm3 and energy efficiency (η) of 80.4% are achieved in the PLZT thin-films under a large breakdown strength (EBD) of 3600 kV/cm. These values are much lower in the PZT thin-films (Ureco of 10.3 J/cm3 and η of 62.4% at EBD of 1000 kV/cm). In addition, the remanent polarization (Pr) and dielectric-constant are also investigated to evaluate the breakdown strength in thin-films. Polar nano-regions (PNRs) are created in the PLZT thin-films to enable relaxor behavior and lead to slim polarization loops along with very small Pr. The excellent operating temperature of energy-storage performance and also the breakdown strength obtained in the PLZT thin-films are mainly ascribed to the presence of PNRs. Moreover, both PZT and PLZT thin-films exhibit superior performance up to 1010 times of charge-discharge cycling.

Excellent energy-storage properties of NaNbO3-based lead-free antiferroelectric orthorhombic P-phase (Pbma) ceramics with repeatable double polarization-field loops

The energy-storage performance of stable NaNbO3-based antiferroelectric (AFE) ceramics was for the first time reported in (0.94-x)NaNbO3-0.06BaZrO3-xCaZrO3 lead-free ceramics. A gradual evolution from an instable AFE phase (x≤0.01) to an orthorhombic AFE P phase (Pbma) (0.01<x≤0.05) was found to accompany the appearance of repeatable double-like polarization versus electric field loops although poled samples (x<0.01) own an AFE monoclinic phase (P21). Interestingly, compared with x≤0.01 samples with instable antiferroelectricity, a relatively high recoverable energy storage density Wrec ˜ 1.59 J/cm3 (@ 0.1 Hz) and a storage efficiency η of ˜30% were achieved in the x = 0.04 ceramic. Moreover, a high Wrec of > 1.16 J/cm3 and an outstanding charge-discharge performance with fast discharge rate (t0.9 < 100 ns) were generated in the temperature range from room temperature to 180 °C in the x = 0.04 ceramic. These results suggest that NaNbO3-based AFE P-phase ceramics could be new potential dielectric materials for high-energy storage capacitors.

Microwave heated lead cobalt titanate nanoparticles synthesized by sol-gel technique: Structural, morphological, dielectric, impedance and ferroelectric properties

The lead cobalt titanate nanoparticles were synthesized via the sol-gel technique followed by microwave heating at 750 °C for 45 min. The X-ray diffraction study revealed the formation of tetragonal PbCoTiO3 phases. The average crystallite size was found to be 26 nm. The surface morphology was examined using field emission scanning and transmission electron microscopes. The dielectric properties such as dielectric constant (ε′), dielectric loss (ε″), ac-conductivity (σac), real (M′) and imaginary part (M″) of dielectric modulus were investigated as a function of temperature and frequency. The impedance analysis was carried out using Cole-Cole plots to elucidate the electrical conduction mechanism. The ferroelectric behavior of PCT was described by polarization versus input electric field (P-E) loop as a function of temperature.

Multiferroic behaviour in B-site Cr-doped hexagonal YInO3 perovskites: Synthesis, structure and properties

New phase pure multiferroic oxides, YIn1-xCrxO3 (x = 0.1, 0.3, 0.5), are synthesized by glycine–aided sol-gel combustion technique using binary oxides and nitrates. YIn0.9Cr0.1O3 (I), YIn0.7Cr0.3O3 (II) and YIn0.5Cr0.5O3 (III) are investigated through powder X-ray diffraction (PXRD), elemental analysis (EDAX), magnetization and polarisation studies. Crystal structure analysis reveals that the sample with 10% Cr3+ (compound I) crystallizes in hexagonal P63cm space group with a = 6.28035 and c = 12.533 Å. The samples with higher concentration of Cr3+ (compounds II and III) crystallize with a mixture of hexagonal and orthorhombic phases. From the detailed magnetic measurements, the compounds are found to exhibit dominating antiferromagnetic behaviour with Neel temperatures of 140, 130 and 125 K for I, II and III, respectively. The Curie-Weiss fittings provide different θ values and the effective magnetic moment, μeff (2.60 μB, to 4.23μB), gradually increases with increasing Cr3+ concentration. The observed values indicate that the spins are not perfectly aligned antiparallel, rather the system exhibits canted antiferromagnetic (AFM) behaviour with weak ferromagnetic interactions. The existence of magnetic ordering is also confirmed by the presence of hysteresis loop below the Neel temperature. The room temperature ferroelectric polarisation loops are indicative of the multiferroic nature of the synthesized compounds. The work reveals the significant role of Cr3+ substitution for structural evolution and enhanced multiferroic behaviour in YIn1-xCrxO3.

Magneto-dielectric and ferroelectric tunability of multifunctional Ce-substituted neodymium zirconate pyrochlores

In this letter, we report the energy storage capacity and magneto-dielectric tenability of rare earth zirconates, by synthesizing a series of Ce-substituted neodymium zirconates having general formula, Nd2Zr2−xCexO7 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0), using sol–gel auto-combustion method. Linear ferroelectric response and energy storage efficiency was checked from polarization loops. Magnetic characterization revealed that rare earth zirconates had small values of coercivity and remanence which argued mainly a superparamagnetic nature of the samples. Tailoring of dielectric properties with the magnetic field and a possible origin of magneto-dielectric coupling was also investigated.

High energy storage performances of Bi1−xSmxFe0.95Sc0.05O3 lead-free ceramics synthesized by rapid hot press sintering

Lead-free Bi1−xSmxFe0.95Sc0.05O3 (x = 0.15–0.19) ceramics were fabricated by rapid hot press sintering, and their structure, ferroelectric and energy storage properties were comprehensively investigated. All the samples are in the mixed phases with R3c rhombohedral and Pbnm orthorhombic structures. With increasing x, the ferroelectric polarization decreases gradually, while the polarization loop becomes gradually slimed too. An high recoverable energy density (˜2.21 J/cm3) and a large efficiency (˜76%) with good thermal stability (20 °C–120 °C) are obtained under electric field (230 kV/cm) for the optimized sample x = 0.17. Moreover, transmission electron microscopy and piezo-response force microscopy measurements reveal that the presence of two-phase coexistence favors the formation of polar nano-regions, leading to the linear-towards polarization behaviors and the enhanced dielectric breakdown field, which is responsible for the superior energy storage performance of Bi1−xSmxFe0.95Sc0.05O3 ceramics. These results indicate a significant step to tailor lead-free BiFeO3-based ceramics towards high dielectric energy storage applications.