Polarization-electric Field Hysteresis Research Articles

Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in ∼ 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb:SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of ∼14.3 µC/cm2, remnant polarization of ∼9.3 µC/cm2 and coercive field ∼1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m-) and o-phases causing an inferior remnant polarization of ∼4.8 µC/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.

Improvement of Energy Storage Properties of NaNbO3-Based Ceramics through a Relaxation Strategy

NaNbO3 (NN) is a widely studied antiferroelectric ceramics in recent years. However, NN ceramics always exhibit a square P-E loop with larger P r, originating form an irreversible antiferroelectric-ferroelectric (AFE-FE) phase transition under an applied electric field and limit the further development. In this paper, a novel lead-free relaxor ferroelectric ceramic, (1−x)NaNbO3-x(0.5Bi0.5Na0.5TiO3−0.5Ba0.3Sr0.7TiO3) [(1−x)NN-xBNBST, x = 0, 0.10, 0.15, 0.20, 0.25, 0.30], was designed and prepared via a local random field relaxation strategy. Dielectric testing show that the addition of BNBST significantly improved the relaxor behavior of the NN, which is effective for enhancing the W rec and η of NN-based ceramics. When x = 0.2, the ceramic obtains a high recoverable energy storage density (W rec = 2.024 J cm−3) and energy storage efficiency (η = 63%) at a low electric field of 130 kV cm−1. Meanwhile, the polarization-electric field (P-E) hysteresis loops and charge-discharge results of the sample with x = 0.2 at different temperatures and frequencies show that it is a prospective material for pulsed energy storage capacitors.

Fabrication and simulation of a piezoelectric PIN-PMN-PT thin film for ultrahigh-frequency ultrasonic transducers

Recently, ultrahigh-frequency (UHF) ultrasonic transducers (> 100 MHz) have been widely applied in research fields such as medical diagnostics, nondestructive testing, energy harvesting, and so on, due to their capability of creating high-resolution ultrasonic images and detecting micro-scale defects. To accomplish this, in this study, ternary Pb(In1/2Nb1/2)O 3 -Pb(Mg1/3Nb2/3)O 3 -PbTiO 3 (i.e., PIN-PMN-PT) polycrystalline single-phase thin film was fabricated for UHF ultrasonic transducers due to their extraordinary piezoelectric properties and electromechanical coupling coefficients. A tri-layered structure (of 1) aluminum substrate, 2) the PIN-PMN-PT thin film, and 3) a silver electrode) was used to create a PIN-PMN-PT thin film compatible with intense thermal treatment and having low cost. To analyze the performance of the newly developed PIN-PMN-PT thin film, data were collected on its crystallographic and piezoelectric characteristics, fabrication process, analysis of piezoelectric constants, and ultrasonic pulse-echo response waveforms according to different design conditions (various front matching layers, backing materials, and media). These data were provided by X-ray diffraction, X-ray fluorescence, X-ray reflectometry, field emission scanning electron microscopy, and polarization-electric field hysteresis curves. Moreover, pulse-echo simulation was conducted using PiezoCAD software based on the Krimholtz-Leedom-Matthaei model. The results showed that the proposed PIN-PMN-PT thin film exhibited ultrahigh-resonance frequencies of ∼ 500 MHz. Ultimately, it was concluded that the new high-frequency PIN-PMN-PT thin film could be applied in a variety of fields because its performance has been verified. • A ternary PIN-PMN-PT single crystal-based thin film for ultrahigh-frequency ultrasonic transducers was fabricated. • The performance of the newly developed PIN-PMN-PT thin film was analyzed in various ways to provide its characteristics. • In addition, pulse-echo simulations were conducted based on the Krimholtz-Leedom-Matthaei model for performance evaluation. • The results showed that the proposed PIN-PMN-PT thin film exhibited ultrahigh-resonance frequencies of ∼ 500 MHz.

Effect of Sn Content on Structure and Piezoelectric Properties of Pb(Zr<sub>0.35</sub>Ti<sub>0.65</sub>)<sub>1-x</sub>Sn<sub>x</sub>O<sub>3</sub>

Pb (Zr0.35Ti0.65)1-xSnxO3 (PZST) piezoelectric ceramics with ABO3 perovskite structure were synthesized using Solid state reaction technique. The piezoelectric, ferroelectric and dielectric behavior of PZST piezoceramics was studied systematically by varying the amount of Sn at fixed Zr/Ti ratio. It was found that sample containing Sn= 0.26 exhibit maximum piezoelectric coefficient of 324 pC/N and minimum tangent loss of 0.009. Decrease in tetragonality and Curie Temperature (Tc) was observed with the increase of Sn content. The polarization–electric field hysteresis loops for all compositions were studied and it was observed that the sample containing Sn= 0.26 exhibit maximum polarization of 0.3C/m2. The synthesized PZST compositions can be utilized for Pressure sensors and maritime SONAR applications. Keywords: Piezoelectric, PZST ceramics, ferroelectric, Domains

Direct observation of geometric and sliding ferroelectricity in an amphidynamic crystal.

Sliding ferroelectricity is a recently observed polarity existing in two-dimensional materials. However, due to the weak polarization and poor electrical insulation in these materials, existing experimental evidences are indirect and mostly based on nanoscale transport properties or piezoresponse force microscopy. We report the direct observation of sliding ferroelectricity, using a high-quality amphidynamic single crystal (15-crown-5)Cd3Cl6, which possesses a large bandgap and so allows direct measurement of polarization-electric field hysteresis. This coordination polymer is a van der Waals material, which is composed of inorganic stators and organic rotators as determined by X-ray diffraction and NMR characterization. From density functional theory calculations, we find that after freezing the rotators, an electric dipole is generated in each layer driven by the geometric mechanism, while a comparable ferroelectric polarization originates from the interlayer sliding. The net polarization of these two components can be directly measured and manipulated. Our finding provides insight into low-dimensional ferroelectrics, especially control of the synchronous dynamics of rotating molecules and sliding layers in solids.

Annealing effects on epitaxial (K,Na)NbO3 thin films grown on Si substrates

Epitaxial (K,Na)NbO3 (KNN) thin films were deposited on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering, and post-annealing effects on the as-deposited epitaxial KNN thin films were investigated. According to the findings, by annealing, the crystal system of these thin films changes from a tetragonal to an orthorhombic system because of the release of internal stress. The asymmetry of polarization–electric field hysteresis loops along the electric field changes from a positive to a negative side by annealing. This means that stable spontaneous polarization P s changes from the upward to downward direction with an increase in the number of A-site vacancies. In addition, the displacement–electric field curves of epitaxial KNN/Si unimorph cantilevers exhibit asymmetric behaviors. A relatively high converse piezoelectric coefficient ∣e 31,f ∣ = 6.4 C m−2 is obtained for 5 h annealed epitaxial KNN thin films.

Integration of Ferroelectric K0.5Na0.5NbO3 films on Si at 400 ℃

In this work, polycrystalline K0.5Na0.5NbO3 (KNN) thin films were successfully integrated on Si at 400 ℃ via a RF magnetron sputtering process. These films showed a polycrystalline bulk-like orthorhombic phase with mixed (00l) and (110) orientations, as was supported by X-ray diffraction and piezoelectric force microscopy analyses. Without a post-deposition annealing process, these films already showed a clear ferroelectric polarization-electric field (P-E) hysteresis loop, characterized by a remnant polarization ~11μC/cm2 and a coercive field of ~280 kV/cm. This polarization response shows a good aging resistance (~2 years). A dielectric constant of ~230 and a low loss tangent of ~1.8 % (@1 kHz) were achieved in the KNN film. Lastly, large dielectric tunabilities of ~50 % (@ 1 MHz) was revealed for the KNN film, illustrating their good potential for applications in tunable dielectrics.

Energy storage and charge-discharge performance of B-site doped NBT-based lead-free ceramics

Dielectric ceramic materials with high energy-storage density and excellent charge-discharge performance are desirable for use in dielectric capacitors. In this study, (Na 0.5 Bi 0.5 ) 0.75 Sr 0.25 TiO 3 – x Nb 2 O 5 (denoted as NBSTN x ) lead-free ceramics were prepared by a solid-state reaction method. Polarization-electric field hysteresis loops ( P–E loops) reflected the energy storage characteristics of the NBSTN x ceramics. Introducing Nb into a pure NBST ceramic can reduce the large remnant polarization ( P r ) and make the P–E loops slimmer. Through repeated trials and calculations, the maximum recoverable energy-storage density ( W rec ~ 3.25 J/cm 3 ) and energy storage efficiency ( η ~ 74.5%) were achieved for the NBSTN 0.03 ceramic at 140 kV/cm. We also tested the stability performance of the NBSTN x ceramics, where the NBSTN 0.03 ceramic exhibited the highest thermal stability (30–100 °C) and frequency stability (10–1000 Hz). The NBSTN 0.03 ceramic also had a fast discharge rate (<300 ns) and a good discharge energy-storage density ( W d ~ 1.80 J/cm 3 ). Therefore, the NBSTN 0.03 ceramic with a good energy-storage density and charge-discharge performance has excellent application prospects for practical dielectric capacitors. • A strategy incorporating B-site doping to enhance energy storage performance. • A relatively high W rec of 3.25 J/cm 3 and η of 74.5%. • Sample with 0.03 mol Nb doping shows relatively good temperature and frequency stability.

Studies of structure, dielectric and conduction mechanism of Bi3+/Yb3+ modified BaTiO3

The present communication aims at the study of the structural, dielectric, electrical and conduction properties of Bi3+/Yb3+ substituted BaTiO3 with a chemical composition of Ba0.5Bi0.5Yb0.5Ti0.5O3. The modified BaTiO3, could be synthesized by a solid state reaction technique. The X-ray diffraction data and pattern revealed the formation of the above compound with tetragonal crystal system. The material's molecular structure (Ba–Ti–O bond, O–Ti–O stretching-mode, metal-oxygen bond, optical band gap, and so on) was determined using room temperature Fourier transform infrared (FTIR) and UV–visible spectroscopic spectra. Detailed investigations of the material's electrical (dielectric/leakage current and impedance) behavior over a wide temperature (250C–5000C) and frequency (1 kHz–1000 kHz) range revealed the presence of capacitive, resistive, and conductive mechanisms. On the investigation of the polarization-electric field (P-E) hysteresis loop on multiple substitution, the change of ferroelectric polarization (spontaneous and residual) and storage density of BaTiO3 was observed. Defect chemistry of the modified barium compound has been discussed in the details.

Enhanced energy storage properties in relaxor Pb(Mg1/3Nb2/3)O3-PbTiO3 thin-film capacitors by incorporating buffer layers

Recently, relaxor ferroelectric thin-film capacitors have attracted considerable attention for energy storage applications since their slim-type polarization–electric field hysteresis loops can yield large recoverable energy density (Wrec) and high efficiency (η). In this work, we study the effects of buffer layers on energy storage properties of 0.93Pb(Mg1/3Nb2/3)O3-0.07PbTiO3 (PMN-PT) thin-film capacitors with a 5 nm-thick SrTiO3 (STO) and LaAlO3 (LAO) films. The energy storage properties of Pt/PMN-PT/SrRuO3 (SRO) capacitors are found to be significantly changed by incorporating the STO or LAO buffer layer at the top Pt/PMN-PT interface, while inserting the buffer layer at bottom PMN-PT/SRO interface shows negligible effects on the electrical properties. Specifically, with the STO buffering, the breakdown field is dramatically increased in the Pt/STO/PMN-PT/SRO capacitor due to the existence of an internal field in the STO, which prevents the growth of electrical trees from the bottom SRO to the top Pt electrode, and a large Wrec of ∼48.91 J/cm3, more than three times of that of the PMN-PT capacitor, is achieved. However, buffered by the LAO, the Pt/LAO/PMN-PT/SRO capacitor exhibits a reduced relaxor character, which may be ascribed to a pinning effect of nanodomains associated with the charged LAO/PMN-PT interface. As a result, both Wrec and η are significantly lowered, compared to the non-buffered PMN-PT capacitor. These results provide physical insights into the modulation of relaxor and dielectric behaviors by designing the characteristics of buffer layers, demonstrating a way for enhancing energy storage properties in thin-film capacitors.

High-Temperature Ferroelectric Behavior of Al0.7Sc0.3N.

Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high−temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.

Ultrahigh energy storage density and superior discharge power density in a novel antiferroelectric lead hafnate

Dielectric capacitors have been widely applied to pulse charge-discharge systems with medium energy density and high power density. In this work, (Pb1-3x/2Lax)Hf0.96Ti0·04O3 (PLHT) antiferroelectric (AFE) ceramics were synthesized by a solid-state solution. The field-induced AFE to ferroelectric transitions with double polarization-electric field hysteresis loops were observed for all studied components. The energy storage efficiency of PLHT ceramics was significantly improved by doping La3+. The sample of x = 0.05 (PLHT-0.05) exhibits excellent energy storage properties with a record-high recoverable energy storage density of 11.2 J/cm3, and a high energy efficiency of 88.9% achieved at an electric field of 360 kV/cm. The ceramic exhibits superior frequency and thermal stability against external environmental change. Besides, a record high discharge energy density (8.51 J/cm3) with an ultrafast discharge rate (t0.9<211 ns) was obtained under 360 kV/cm at room temperature in PLHT-0.05 ceramic. Underdamped discharge test shows the sample achieves an ultrahigh current density of 2098 A/cm2 and a giant power density of 378 MW/cm3, suggesting a significant advantage compared with the previously reported ceramic systems. The significant improvement implies the PLHT AFE ceramics can provide a realistic solution for high-power energy storage capacitors.

Bimodal polymorphic nanodomains in ferroelectric films for giant energy storage

Enhanced functional responses of ferroelectrics have often been achieved by complex compositional design of a morphotropic or polymorphic phase boundary. Here, we observe a pseudo-linear, ultra-slim polarization-electric field (P-E) hysteresis loop in simple composition, lead-free Ba(Zr,Ti)O3 of up to μm-thick. It features a low remnant polarization and a high maximum polarization after a delayed saturation process with a field-insensitive, thickness-scalable high energy efficiency of ∼90%. This giant energy storage performance is attributed to the self-assembled, bimodal polymorphic nanodomains consisting of two sets of coherent polymorphic nanodomains. The first set of domains has the best-matched, low index {110} interface. They manifest themselves as “entangled nanophases” and dominate in thinner or annealed films. The 2nd set of domains with a high-index {114} interface and an in-plane anisotropy leads to the largest reduction in bulk elastic energy. These domains show as “segregated nanophases” and prevail in as-grown thick films. The presence of multi-polar states in both sets of nanodomains helps reduce the remnant polarization and delay the polarization saturation. Furthermore, the segregated tetragonal phase in-plane nanodomains lead to a larger maximum polarization under a high poling field. Strain engineering of such nanodomain structures provides a promising alternative to chemical compositional design, for the optimization of dielectric thin films used in capacitive energy storage applications.

Ferroelectric Lithography in Single‐Component Organic Enantiomorphic Ferroelectrics

AbstractOrganic ferroelectrics are flexible, lightweight, and bio‐friendly, promising for bio‐harmonized electronic devices, while their ferroelectric lithography remains relatively unexplored. Here, by introducing homochirality and ZE photoisomerization, we obtained a pair of organic enantiomorphic ferroelectrics, di(benzylamino)‐substituted derivatives of muconic acids, the first ferroelectrics in the muconic family. Their ferroelectric and chiral features were confirmed by the polarization–electric field hysteresis loops and circular dichroism spectra, respectively. Piezoresponse force microscopy measurements demonstrate that the desired domain structure can be precisely achieved by applying a local electric field on a predefined pattern in their thin films. Moreover, thermogravimetric analyses reveal that their ferroelectricity can persist up to above 550 K. The precise pattern lithography and excellent thermal stability make them competitive candidates for ferroelectric lithography.

Ferroelectric Lithography in Single-Component Organic Enantiomorphic Ferroelectrics.

Organic ferroelectrics are flexible, lightweight, and bio-friendly, promising for bio-harmonized electronic devices, while their ferroelectric lithography remains relatively unexplored. Here, by introducing homochirality and ZE photoisomerization, we obtained a pair of organic enantiomorphic ferroelectrics, di(benzylamino)-substituted derivatives of muconic acids, the first ferroelectrics in the muconic family. Their ferroelectric and chiral features were confirmed by the polarization-electric field hysteresis loops and circular dichroism spectra, respectively. Piezoresponse force microscopy measurements demonstrate that the desired domain structure can be precisely achieved by applying a local electric field on a predefined pattern in their thin films. Moreover, thermogravimetric analyses reveal that their ferroelectricity can persist up to above 550 K. The precise pattern lithography and excellent thermal stability make them competitive candidates for ferroelectric lithography.

Deferred Polarization Saturation Boosting Superior Energy-Storage Efficiency and Density Simultaneously under Moderate Electric Field in Relaxor Ferroelectrics

High-temperature dielectric Bi0.5Na0.5TiO3 (BNT)-based relaxors near a morphotropic phase boundary are developed with excellent energy storage performance. Random distribution of polar nanoregions induced by composition modulation would disrupt the ferroelectric long-range dipolar alignment and weaken the coupling between the ferroelectric domains, yielding slender and deferred polarization–electric field hysteresis loops with relatively high saturation polarization. The reversible nano-domain orientation and growth in relaxors under a delayed electric field result in negligible remnant polarization and advantageous energy storage properties. Simultaneously, superior recoverable energy storage density and efficiency are gained, significantly surpassing the state-of-the-art dielectric energy storage materials under similar moderate electric fields. Vacancies, defect dipole behavior, and structural evolution that relied on an electric field and temperature are discussed to disclose the underlying mechanism associated with phase transition. Even thermal stability and large electrostrictive strain with low hysteresis are achieved in elevated temperatures. These features demonstrate the promising candidates for dielectric energy-storage application and provide a strategy in designing relaxors.

Explicating the irreversible electric-field-assisted ferroelectric phase transition in the otherwise antiferroelectric sodium niobate for energy storage systems

By means of a first-principles-based Landau–Devonshire model, we predict and explain why newly discovered intermediates can rationalize the persistent lack of a double polarization–electric field hysteresis for NaNbO3 under an applied field.

Ferroelectric properties of ZrO2 films deposited on ITO-coated glass

In this work, the ferroelectric characteristics of ZrO2 thin films grown on ITO-coated glass have been investigated. The ferroelectric nature of the ZrO2 films has been studied by polarization-electric field (P-E) hysteresis loops and found to be optimum for the films processed by rapid thermal annealing at 600 °C. The increase in the annealing temperature improves the ferroelectric properties through the increase of the in-plane strain that causes the formation of the ferroelectric orthorhombic phase. The formation of the orthorhombic phase was confirmed through high-resolution transmission electron microscopy. The effect of the electric field on the polarization switching kinetics of ZrO2 films has been investigated revealing that the switching kinetics follows the nucleation limited switching (NLS) model. The activation fields estimated from the peak values of the polarization currents (im) and the time (tm) at which im occurs are in good agreement with the values obtained from the switching characteristic time of the NLS model. This work paves the way towards the integration of (pseudo)-binary oxide thin films on cheap substrates like glass for the next-generation of non-volatile memories.

Ferroelectric and Dielectric Properties of Strontium Titanate Doped with Barium

Ferroelectric samples Sr1−xBaxTiO3 (BST), where x = 0, 0.2, 0.4, 0.6, 0.8 and 1, were prepared using the tartrate precursor method and annealed at 1200 °C for 2 h. X-ray diffraction, “XRD”, pattern analysis verified the structure phase. The crystallite size of the SrTiO3 phase was calculated to be 83.6 nm, and for the TiO2 phase it was 72.25 nm. The TEM images showed that the crystallites were agglomerated, due to their nanosize nature. The AC resistivity was measured as temperature dependence with different frequencies 1 kHz and 10 kHz. The resistivity was decreased by raising the frequency. The dielectric properties were measured as the temperature dependence at two frequencies, 1 kHz and 10 kHz. The maximum amount of dielectric constant corresponded to the Curie temperature and the transformation from ferroelectric to paraelectric at 1 kHz was sharp at 10 kHz. Polarization–electric field hysteresis loops for BST samples were measured using a Sawer–Tawer modified circuit. It was shown that the polarization decreased with increasing temperature for all samples.

Ferroelectric and magnetic properties in ε-Fe2O3 epitaxial film

The phase stability, ferroelectricity, and magnetism of highly crystalline epitaxial ε-Fe2O3 films deposited on SrTiO3(111) substrates are reported. Temperature-dependent x-ray diffraction measurements revealed that α-Fe2O3 appeared as a secondary phase after samples were annealed up to 1000 °C. A clear saturated and opened polarization–electric field hysteresis loop with the remnant polarization ∼2.6 μC cm−2 and coercive electric field ∼100 kV cm−1 was obtained at room temperature using a conventional ferroelectric measurement technique. The magnetic phase transition was observed at 155 K. Magnetization–magnetic field measurements revealed that magnetic softening via the phase transition accompanied a reduction in the coercive field from 10 to 6.8 kOe, which is smaller than the coercive field reduction previously observed for ε-Fe2O3 nanoparticles.