Large Saturated Polarization Research Articles

Epitaxial Single‐Crystalline PZT Thin Films on ZrO2‐Buffered Si Wafers Fabricated Using Spin‐Coating for Mass‐Produced Memristor Devices

AbstractA Pb(Zr0.52Ti0.48)O3(PZT) thin film is fabricated on SrRuO3(SRO)/Pt/ZrO2/Si, and its resistive switching properties are thoroughly investigated. The ZrO2thin film serves as a buffer layer for the epitaxial growth of single‐crystalline PZT thin films, and spin‐coating fabrication is useful for introducing a suitable defect content to achieve effective resistive switching in PZT. The present PZT thin film exhibits improved ferroelectric properties compared with most of the spin‐coated or sol‐gel prepared PZT films reported previously, with a large saturation polarization of ≈43 µC cm−2and coercive filed of ≈700 kV cm−1. The symmetrically reversed true‐remanent hysteresis shows no evident imprint effect and a fully saturated polarization is observed. Intrinsic ferroelectric properties indicate the presence of non‐switching components that are conducive to memory applications. Butterfly shaped electrical conduction reveals resistive switching behavior, with abnormal bipolar resistive switching (BRS) at low voltages and normal BRS at high voltages. The abnormal BRS is explained by a microscopic mechanism involving ferroelectric polarization and an induced dipole moment, whereas the normal BRS is studied by fitting different conducting models and is dominated by interfacial barriers and defects. This study presents a progressive strategy for the large‐scale production of ferroelectric perovskite thin films, specifically suitable for silicon‐based memristors.

Achieving large negative electrocaloric effect in AgNbO3-based antiferroelectric ceramics based on dipole disordering

The electrocaloric effect (ECE) is considered as an environmentally friendly refrigeration technology, which can be used to replace vapor compression refrigeration. Lead-free antiferroelectric (AFE) ceramics are promising electrocaloric materials because of large saturation polarization and polarization change with temperature, which can generate large positive or negative ECE. In this work, the lead-free Ag(Nb1-0.8xHfx)O3 (x = 0, 0.001 and 0.003) AFE ceramics are fabricated through a conventional solid-state reaction method which shows a decreased the phase transition temperature of M1 - M2 toward room temperature (RT), and a large negative ECE (ΔT = −2.3 K under 130 kV cm−1) is obtained near the ambient temperature by using an indirect measurement in ANH0.001 AFE ceramic. The large negative ECE behavior is ascribed to dipole disordering (i.e. the anti-parallel dipoles are broken and gradually becomes disordered under an external electric field) resulting from the field-induced phase transition under a modest electric field. This work shows that AgNbO3-based AFE ceramics could be used in the refrigeration devices as an electrocaloric material.

The effect of interfacial charge-induced multiferroic properties of Bi0.993La0.007FeO3/BaTiO3 bilayer thin films: Performance modulation and energy storage applications

Multifunctional and multiferroic materials assure a tantalizing perspective of applications in next-generation microelectronics, memory, energy harvesting, and energy storage technologies. The current study aims to deposit a bilayer thin film of BLFO/BTO with varying top layer (BLFO) thickness on n-type Si and Pt/Ti/SiO2/Si (Pt-Si) substrate by the PLD technique. Bilayer films with dense and packed microstructures show evidence of both tetragonal (T) and rhombohedral (R) symmetry. The bilayer films exhibit remarkably enhanced saturation magnetization of 35.9 emu/cm3 and improved maximum polarization of 34 μC/cm2 at RT compared to single-layer films. Moreover, the higher top layer thickness (BTO/BLFO3) hetero-structures achieved a high recoverable energy storage density of 11.65 J/cm3 with an energy efficiency of 85 % simultaneously. These films display excellent energy storage performance and produce a maximum power density of 0.9 MW/cm3 at 100 Hz. Further, the leakage current density of BLFO/BTO3 film is found ∼102 times lower than the monolayer BTO thin film suggesting the lower oxygen vacancies, defects, and impurities in the bilayer stacked films with higher top layer thickness. The drop in leakage current density, slim hysteresis loop, and enhancement in large saturation polarization for BTO/BLFO3 highlight the improved result demonstrating the interface effect and coupling between ferroelectric and magnetic properties. Hence, the acquired ferroelectric and magnetic properties are promising for spintronic devices and energy storage capacitor applications.

Stabilizing polar P21ma phase in Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 relaxors by CaTiO3 additive to promote energy storage density, efficiency and discharge rate

Eco-friendly Bi0.5Na0.5TiO3 relaxor ferroelectric has attracted considerable attention for pulsed power capacitor applications due to its large saturation polarization. However, high remnant polarization and low breakdown strength (Eb) restrict its application. Herein, linear dielectric CaTiO3 (CT) is introduced into Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 (BNT-NBNM) ceramic to enhance its Eb. Interestingly, CT additive can stabilize polar orthorhombic P21ma phase. As a result, a high recoverable energy density of 6.4 J/cm3 and a high efficiency of 92% at 400 kV/cm as well as an ultrafast discharge rate of 57 ns are obtained in 0.63BNT-0.27NBNM-0.1CT ceramic. Furthermore, temperature dependent Raman spectra reveal that the superior temperature stability of energy storage properties over the temperature span of 30–150 °C is due to insensitive B-O vibration to temperature. The results demonstrate an effective strategy to construct superior and stable BNT-based energy storage materials for pulsed power capacitor applications.

Stable self-polarization in lead-free Bi(Fe0.93Mn0.05Ti0.02)O3 thick films

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 [Formula: see text]m-thick Bi([Formula: see text][Formula: see text][Formula: see text])O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 [Formula: see text]C/cm2, and a remanent polarization of 70 [Formula: see text]C/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field ([Formula: see text]) loops with a positive shift along the [Formula: see text]-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of [Formula: see text] loops on frequency (1–50 kHz) and temperature (25–125[Formula: see text]C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.

An organic plastic ferroelectric with high Curie point.

Plastic ferroelectrics, featuring large entropy changes in phase transitions, hold great potential application for solid-state refrigeration due to the electrocaloric effect. Although conventional ceramic ferroelectrics (e.g., BaTiO3 and KNbO3) have been widely investigated in the fields of electrocaloric material and catalysis, organic plastic ferroelectrics with a high Curie point (Tc) are rarely reported but are of great importance for the sake of environmental protection. Here, we reported an organic plastic ferroelectric, (−)-camphanic acid, which crystallizes in the P21 space group, chiral polar 2 (C2) point group, at room temperature. It undergoes plastic paraelectric-to-ferroelectric phase transition with the Aizu notation of 23F2 and high Tc of 414 K, showing large entropy gain (ΔSt = 48.2 J K−1 mol−1). More importantly, the rectangular polarization–electric field (P–E) hysteresis loop was recorded on the thin film samples with a large saturated polarization (Ps) of 5.2 μC cm−2. The plastic phase transition is responsible for its multiaxial ferroelectric feature. This work highlights the discovery of organic multiaxial ferroelectrics driven by the motive of combining chirality and plastic phase transition, which will extensively promote the practical application of such unique functional materials.

Room-temperature large magnetoelectricity in a transition metal doped ferroelectric perovskite

There is increasing interest in novel magnetoelectric (ME) materials that exhibit robust ME coupling at room temperature (RT) for advanced memory, energy, spintronics, and other multifunctional device applications, by making use of the ability to control polarization with a magnetic field and/or magnetization via an electric field. Obtaining ME materials with strong ME coupling, understanding the origin, and manipulating its processing along with composition to realize large ME coefficients at RT constitute an important step in multiferroic research. To address this, we have investigated the multiferroic and ME properties of Ni-doped $\mathrm{Pb}({\mathrm{Zr}}_{0.20}{\mathrm{Ti}}_{0.80}){\mathrm{O}}_{3}$ (PZT). We find that the ferroelectric $({T}_{\mathrm{C}}\ensuremath{\sim}700\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ and weak ferromagnetic (\ensuremath{\sim}602 K) phase transitions of Ni-doped PZT are well above room temperature (RT), leading to a strong ME coupling coefficient (${\ensuremath{\alpha}}_{E,31}$) of $11.7\phantom{\rule{0.16em}{0ex}}\mathrm{mV}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--1}\phantom{\rule{0.16em}{0ex}}{\mathrm{Oe}}^{--1}$ (${H}_{\mathrm{ac}}=1\phantom{\rule{0.16em}{0ex}}\mathrm{Oe}$ and $f=1\phantom{\rule{0.16em}{0ex}}\mathrm{kHz}$). While x-ray diffraction suggests a single-phase material, high-resolution transmission electron microscopy reveals regions with and without Ni present; thus magnetoelectric coupling between two phases is possible. First-principles calculations suggest the $(\mathrm{N}{\mathrm{i}}_{\mathrm{Pb}}{)}^{\ifmmode\times\else\texttimes\fi{}}$ defect is likely to be responsible for the experimental observed magnetism and ME coupling in Ni-doped PZT. We further demonstrate that Ni-doped PZT exhibits low loss tangent, low leakage current, large saturation polarization, and weak ferromagnetism. Ultimately, our work demonstrates that Ni-doped PZT is a cost-effective RT multiferroic with strong ME coupling.

Significantly enhanced energy storage density and efficiency of BNT-based perovskite ceramics via A-site defect engineering

In recent years, sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT) -based relaxor ferroelectrics have attracted more and more attention for energy storage applications owing to their high power density, large saturated polarization (PS)/maximum polarization (Pmax) as well as meeting the needs of environment-friendly society. However, the recoverable energy storage density (Wrec) and energy storage efficiency (η) of most BNT-based relaxor ferroelectric ceramics are lower than 3.5 ​J ​cm−3 and/or 80%, respectively, in recently. In this work, the relaxor ferroelectric ceramics of 0.75Bi(0.5+x)Na(0.5-x)TiO3-0.25SrTiO3 (BNST-x) were constructed via A-site defect engineering and prepared by tape-casting method. It is worth noting that an ultrahigh Wrec of 5.63 ​J ​cm−3 together with outstanding η of 94% can be achieved simultaneously at a relative high electric field of 535 ​kV ​cm−1 with the composition of BNST-0.08, Meanwhile, for BNST-0.08 ceramic, the η is higher than 90% and the variation of Wrec is less than ±2% and ±5% within the frequency range of 1–100 ​Hz and temperature range of 30–130 ​°C, respectively. The Wrec is always higher than 3 ​J ​cm−3 and did not deteriorate significantly after 104 fatigue cycles. In addition, the BNST-0.08 ceramic also possesses ultrafast discharge speed (t0.9, less than 125 ​ns) and ultrahigh power density (PD, higher than 147 ​MW ​cm−3) within the temperature range of 30–130 ​°C at 300 ​kV ​cm−1. Therefore, the BNST-0.08 ceramic is promising candidate environment-friendly materials for advanced pulsed power capacitor applications and the energy storage properties of BNT-based relaxor ferroelectrics can be enhanced significantly via A-site defect engineering.

Enhanced energy density and discharged efficiency of lead-free relaxor (1-x)[(Bi0.5Na0.5)0.94Ba0.06]0.98La0.02TiO3-xKNb0.6Ta0.4O3 ceramic capacitors

Ceramic capacitors have optimistic application prospects in the field of high power density energy storage. However, most of the investigations have sought to increase energy storage density (W), but ignore the importance of energy storage efficiency (η). In this work, the novel KNb0.6Ta0.4O3-modified [(Bi0.5Na0.5)0.94Ba0.06]0.98La0.02TiO3 ceramics were designed and prepared. Particularly, the long-range order of ferroelectricity for the ceramic is broken due to the addition of KNb0.6Ta0.4O3 (KNT), which causes shoulder dielectric peak (Ts) to move towards low temperatures and increases the content of weakly polar phase. Therefore, the remanent polarization Pr is effectively decreased, but the large saturation polarization Ps is maintained, leading to simultaneously high η and large W. Moreover, the addition of KNT significantly reduces the grain size, causing an enhanced dielectric breakdown strength (DBS). As a result, ultra-high values for η of 92.9% and Wrec of 2.1 J/cm3 are realized in the ceramic with x = 0.10, which are superior to most of the reported ceramic capacitors under the similar electric field. More importantly, the ceramic exhibits excellent thermal (25–150 °C) and frequency stability (5–105 Hz). The present strategy of adjusting the Ts and weakly polar phase provides a promising approach to design novel Bi0.5Na0.5TiO3-based materials with excellent energy storage performance.

Bendable Bi(Fe0.95Mn0.05)O3 ferroelectric film directly on aluminum substrate

With the rapid development of intelligent electronic system, portable, wearable, and smart electronics with excellent electrical performances and mechanical deformations are needed. This work presents a simple one-step way to construct a bendable Bi(Fe0.95Mn0.05)O3 (BFOMn) film capacitor by the assistant of aluminum metal substrate, which can be used as the substrate and bottom electrode simultaneously. The BFOMn film shows a polycrystalline structure and dense surface morphology. The BFOMn ferroelectric element shows a large remanent polarization (Pr∼68 μC/cm2) and saturated polarization (Ps∼80 μC/cm2) due to the low leakage current (∼2 × 10−5 A/cm2 at 150 kV/cm). A high dielectric constant of 196 and a small loss tangent of 0.05 are obtained at a frequency of 100 kHz. The film also displays outstanding thermal stability over a wide temperature range from 25 to 150 °C. More significantly, even the capacitor is bent to a minor radius of 2 mm, there is no obvious deterioration in polarization, and the film possesses excellent fatigue resistance (109 cycles). These findings are respected to promote the advancement of bendable BiFeO3-based ferroelectric memories for information storage and data processing, which will exhibit an anticipating future in next-generation smart flexible electronics.

Improved energy storage properties of Sr(Zr0.8Nb0.16)O3-doped Bi0.47Na0.47Ba0.06TiO3 ceramics with excellent temperature/frequency stability

Lead-free perovskite dielectric materials for capacitors have received wide concern in recent years, but their energy storage density and efficiency still cannot meet the growing application demand for practical applications. In this work, we prepared a lead-free relaxor ferroelectric ceramic of (1-x)Bi0.47Na0.47Ba0.06TiO3-xSr(Zr0.8Nb0.16)O3, which was synthesized via a normal solid-state route. The microstructure, dielectric properties and energy storage behavior of the ceramics were explored. The ceramics can be well sintered and situated in the region where rhombohedral and tetragonal phases coexist. The addition of Sr(Zr0.8Nb0.16)O3 (SZN) significantly extends the dielectric-temperature plateau between Ts and Tm and reduces the remnant polarization Pr, but the large saturation polarization Ps is still maintained. Besides, the doping of SZN enhances the relaxation of the material and increases the dielectric breakdown strength (DBS) from 50 kV/cm (x = 0) to 100 kV/cm (x = 0.04 and 0.06). Therefore, the ceramic with x = 0.06 exhibits a high discharging efficiency (η) of 71.1% and energy density (W) of 1.56 J/cm3 at 100 kV/cm and shows the superior thermal stability with the changes in recoverable energy density (Wrec) and η of less than 10% and 30% at the temperature range of 25–180 °C and the excellent frequency stability with the variations of Wrec and η of less than 1.8% and 1% at the frequency range of 10 Hz–100 Hz.

Large Polarization and Susceptibilities in Artificial Morphotropic Phase Boundary PbZr1−xTixO3 Superlattices

AbstractThe ability to produce atomically precise, artificial oxide heterostructures allows for the possibility of producing exotic phases and enhanced susceptibilities not found in parent materials. Typical ferroelectric materials either exhibit large saturation polarization away from a phase boundary or large dielectric susceptibility near a phase boundary. Both large ferroelectric polarization and dielectric permittivity are attained wherein fully epitaxial (PbZr0.8Ti0.2O3)n/(PbZr0.4Ti0.6O3)2n (n = 2, 4, 6, 8, 16 unit cells) superlattices are produced such that the overall film chemistry is at the morphotropic phase boundary, but constitutive layers are not. Long‐ (n ≥ 6) and short‐period (n = 2) superlattices reveal large ferroelectric saturation polarization (Ps = 64 µC cm−2) and small dielectric permittivity (εr ≈ 400 at 10 kHz). Intermediate‐period (n = 4) superlattices, however, exhibit both large ferroelectric saturation polarization (Ps = 64 µC cm−2) and dielectric permittivity (εr = 776 at 10 kHz). First‐order reversal curve analysis reveals the presence of switching distributions for each parent layer and a third, interfacial layer wherein superlattice periodicity modulates the volume fraction of each switching distribution and thus the overall material response. This reveals that deterministic creation of artificial superlattices is an effective pathway for designing materials with enhanced responses to applied bias.

Excellent thermal stability of large polarization in (Bi0.5Na0.5)TiO3-BaTiO3 thin films induced by defect dipole

This work reports the large saturation polarization (Pm) of ~80 µC/cm2 and remnant polarization (Pr) of ~60 µC/cm2 in Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 (BNBTMn) thin films at elevated temperatures, which are substantially higher than the best values of the bulk counterparts, i.e. Pm (~40 µC/cm2) and Pr (~30 µC/cm2). The positive-up-negative-down (PUND) data suggested the contribution of switchable ferroelectric Pr is less than 50% in the overall Pr obtained in P-E loops at 300 K and keeps decreasing when heating. Thus, the observed large and thermally stable macroscopic polarizations in P-E loops is mainly attributed to the contribution of conformed local defect dipoles, namely MnTi′-Vo•• (oxygen vacancy), under a strong electric field. The evolution of Raman spectra with temperature further confirm the presence of symmetry breaking associated with local polar in our BNBTMn thin films can be remained up to 750 K, much higher than previous reported Curie temperature. This work will shed light on the development of high-temperature nano-scale ferroelectric memories and other related devices with eco-friendly materials.

Energy storage in BaBi4Ti4O15 thin films with high efficiency

A ferroelectric film with slim polarization-electric (P-E) hysteresis loops, showing small remanent polarization (Pr) and large saturated polarization (Ps), is desired to obtain high recoverable energy density (Ure) and efficiency (η) in thin film capacitors. Here, small Pr and large Pm values are achieved in BaBi4Ti4O15 thin films through modulating film grain size. A large Ure of 44.3J/cm3 as well as a high η of 87.1% is obtained. In addition, the derived BaBi4Ti4O15 thin films show excellent energy storage performance in wide frequency range, thermal stability, and fatigue endurance. These results suggest that BaBi4Ti4O15 films can be considered as a candidate for dielectric energy storage capacitors, and the route through grain size optimization is a promising strategy to improve the capacitive performance of ferroelectric materials.

Exploring the Magnetoelectric Coupling at the Composite Interfaces of FE/FM/FE Heterostructures

Multiferroic materials have attracted considerable attention as possible candidates for a wide variety of future microelectronic and memory devices, although robust magnetoelectric (ME) coupling between electric and magnetic orders at room temperature still remains difficult to achieve. In order to obtain robust ME coupling at room temperature, we studied the Pb(Fe0.5Nb0.5)O3/Ni0.65Zn0.35Fe2O4/Pb(Fe0.5Nb0.5)O3 (PFN/NZFO/PFN) trilayer structure as a representative FE/FM/FE system. We report the ferroelectric, magnetic and ME properties of PFN/NZFO/PFN trilayer nanoscale heterostructure having dimensions 70/20/70 nm, at room temperature. The presence of only (00l) reflection of PFN and NZFO in the X-ray diffraction (XRD) patterns and electron diffraction patterns in Transmission Electron Microscopy (TEM) confirm the epitaxial growth of multilayer heterostructure. The distribution of the ferroelectric loop area in a wide area has been studied, suggesting that spatial variability of ferroelectric switching behavior is low, and film growth is of high quality. The ferroelectric and magnetic phase transitions of these heterostructures have been found at ~575 K and ~650 K, respectively which are well above room temperature. These nanostructures exhibit low loss tangent, large saturation polarization (Ps ~ 38 µC/cm2) and magnetization (Ms ~ 48 emu/cm3) with strong ME coupling at room temperature revealing them as potential candidates for nanoscale multifunctional and spintronics device applications.

Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial ferroelectric films is demonstrated. Scanning transmission electron microscopy (STEM) indicates that the polarization of a pristine film deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization field with respect to the out-of-plane direction. Applying an electric field aids in ferroelastic domain switching in YHO-7 films. Such films exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 μC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90° domain switching as the odd number reflection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a significant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.

Energy storage properties of NaNbO3-CaZrO3 ceramics with coexistence of ferroelectric and antiferroelectric phases

Anti-ferroelectric materials with large saturated polarization, small remnant polarization, and moderate breakdown strength are receiving increasing attention for modern high-power electrical systems. Here we demonstrated that by incorporating CaZrO3 into NaNbO3 ceramics, the antiferroelectricity in NaNbO3-CaZrO3 solid solutions could be stabilized at room temperature. The effects of phase constitution and microstructure on the dielectric properties, electrical breakdown strength, and energy storage properties of the NaNbO3-CaZrO3 ceramics were investigated. Ferroelectric and antiferroelectric phase coexistence in the NaNbO3-CaZrO3 was confirmed by XRD and TEM analyses. With increasing CaZrO3 content, the grain size was reduced, and the dielectric breakdown strength was improved. Therefore, a high energy density of 0.55 J/cm3 and efficiency of 63% was obtained in the NaNbO3-0.04CaZrO3 ceramics. These lead-free NaNbO3-CaZrO3 antiferroelectrics with good electrical energy storage can be exploited for high-power storage devices.

0–3 type Bi3TaTiO9:40wt%BiFeO3 composite with improved high-temperature piezoelectric properties

The 0–3 type Bi3TaTiO9:xwt%BiFeO3 composites are fabricated by embedding the isolated BiFeO3 (BFO) grains in the Bi3TaTiO9 (BTTO) matrix to acquire the merits of both materials, i.e. high piezoelectric d33 of BFO and high resistance of BTTO at high temperature. Bi3TaTiO9:40wt%BiFeO3 composite shows the high resistance of ∼1010 Ω, the large saturated polarization of 33.7 μC/cm2, the high piezoelectric d33 of 24 pC/N, the large electromechanical coupling coefficients and high Curie temperature (TC > 800 °C). Most importantly, the composite maintains a very high resistance even at 500 °C and the d33 of 21 pC/N after annealing at 600 °C. In a word, the 0–3 type composite shows much better high-temperature piezoelectric performances than those of either BFO or BTTO and it is promising to be used in high-temperature piezoelectric devices.

Energy Storage Characteristics of BiFeO₃/BaTiO₃ Bi-Layers Integrated on Si.

BiFeO3/BaTiO3 bi-layer thick films (~1 μm) were deposited on Pt/Ti/SiO2/(100) Si substrates with LaNiO3 buffer layers at 500 °C via a rf magnetron sputtering process. X-ray diffraction (XRD) analysis revealed that both BiFeO3 and BaTiO3 layers have a (00l) preferred orientation. The films showed a small remnant polarization (Pr ~ 7.8 μC/cm2) and a large saturated polarization (Ps ~ 65 μC/cm2), resulting in a slim polarization-electric field (P-E) hysteresis loop with improved energy storage characteristics (Wc = 71 J/cm3, η = 61%). The successful “slim-down” of the P-E loop from that of the pure BiFeO3 film can be attributed to the competing effects of space charges and the interlayer charge coupling on charge transport of the bi-layer film. The accompanying electrical properties of the bi-layer films were measured and the results confirmed their good quality.

Polarization switching characteristics of 0.5BaTi0.8Zr0.2O3-0.5Ba0.7Ca0.3TiO3 lead free ferroelectric thin films by pulsed laser deposition

We report on the ferroelectricity for morphotropic-phase-boundary lead (Pb) free 0.5BaTi0.8Zr0.2O3-0.5Ba0.7Ca0.3TiO3 (0.5BZT-0.5BCT) thin films. Thin films were grown on Pt/Ti/SiO2/Si substrate using pulsed laser deposition. Raman spectroscopic data combined with the X-ray diffraction analyses confirm body centered tetragonal crystallographic structure 0.5BZT-0.5 BCT thin films on Pt/Ti/SiO2/Si. Polarization studies demonstrate that these 0.5BZT-0.5BCT films exhibit a large remnant and saturation polarization of 37 μC/cm2 and 40 μC/cm2, respectively, with a coercive field of 140 kV/cm. A correlation between polarization dynamics, structural distortion, and phonon vibration is established. The splitting of X-ray diffraction peak of the thin film in the 2θ range of 44.5° to 46.5° represents high degree of tetragonality. The tetragonality factor calculated by Rietveld analysis was found to be 0.006 and can be a major cause for the increased remnant polarization value. It is established from Raman spectra that the non-centrosymmetricity due to the displacement of Ti/Zr ions from its octahedral position is related to the peak position as well as the broadening of the A1 (LO) optical phonon mode. This increase of broadness in the thin film causes an increase in the dipole moment of the unit cell and, hence, the net increase in polarization values.