Large Remnant Polarization Research Articles

Enhanced Mechanical Properties of Mn- and Fe-Doped Na0.5Bi0.5TiO3 Ceramics.

The mechanical properties of Mn- and Fe-doped Na0.5Bi0.5TiO3 ceramics in unpoled and poled states were examined and analyzed for the first time through measurements of Young's modulus, the elastic modulus, Poisson's number, compressibility modulus K, hardness, fracture toughness and bending strength on one hand and by stress-strain measurements on the other hand. It was found that both the introduction of Fe and Mn ions into Na0.5Bi0.5TiO3 and E-poling lead to improvements in their mechanical properties. The additives also cause improvement of the piezoelectric properties. The stress-strain curves revealed a changing mechanical response with the Mn and Fe doping of the NBT. With the doping, there was a decrease in coercive stress, which enhanced the remnant strain. In contrast, the E-poling led to an increase in the coercive stress, which reduced the remnant strain. Induced internal stresses associated with non-180° domain switching were determined. It was found that the investigated materials displayed significant ferroelastic deformation and large remnant polarization even under external stress of 180-250 MPa. Modification of NBT by Mn and Fe ions and E-poling were found to be effective ways of improving actuator performance and controlling operating stresses in order to minimize irreversible fatigue damage. The results suggest that the investigated materials could replace PZT ceramics in actuator applications where high blocking stress is required.

Simultaneous achievement of high energy storage density and ultrahigh efficiency in BCZT-based relaxor ceramics at moderate electric field

The development of high-performance energy storage dielectric materials is the key to the development of large capacity ceramic capacitor. How to obtain the high energy storage density and efficiency of dielectric materials is the basis. Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) has high energy storage potential as a typical piezoelectric material, but it shows poor energy storage properties due to low breakdown electric field and large remnant polarization. In this work, we propose a combined optimization strategy aimed at enhancing the comprehensive energy storage performance of BCZT-based ceramics through doping with bismuth-based oxides. The diverse phase morphology offers substantial potential for modifying the electrical properties of BCZT-based ceramics. Electrical homogeneity is markedly improved with the incorporation of Bi2/3(Al1/2Nb1/2)O3 (BAN), which is accompanied by a reduction in long-range ferroelectric phases and the emergence of polar nanoregions. Ultimately, optimal BCZT-xBAN ceramics with x = 0.09 exhibit superior energy storage performances (Wrec ∼ 3.71 J/cm3, η ∼ 94.54 %) under moderate electric fields. Furthermore, BCZT-0.09BAN ceramics demonstrate commendable fatigue endurance, frequency stability, and temperature stability characteristics; notably achieving an ultrafast discharge rate of t0.9–14.6 ns alongside excellent discharge properties (CD ∼ 1278.66 A/cm2, PD ∼ 191.80 MW/cm3, WD ∼ 1.57 J/cm3).

High energy storage performance of KNN-based relaxor ferroelectrics in multiphase-coexisted superparaelectric state

Although K0.5Na0.5NbO3 (KNN) possesses large maximum polarization and relatively high breakdown strength, the large remnant polarization constrains their practical applications as energy storage materials. In this work, through multi-element doping, (K0.5−0.5xNa0.5−0.5xBix)(Nb1−xSn0.2xZn0.6xTa0.2x)O3 relaxor ferroelectrics were prepared. As the superparaelectric states (SPE) were adjusted to room temperature, orthorhombic, tetragonal, and cubic phases coexisted, accompanied by the highly dynamic polar nanoregions (PNRs). In particular, a high recoverable energy storage density of 4.5 J/cm3 and an energy storage efficiency of 83% were achieved for the x = 0.125 ceramic, with the variations less than 11% and 4%, respectively, in the wide temperature range of 20–180 °C. These results demonstrate that the multiphase PNRs in the SPE state is an effective strategy for improving the energy storage performance of KNN-based ceramics.

Low-Temperature Fabrication of BiFeO3 Films on Aluminum Foils under a N2-Rich Atmosphere.

To be CMOS-compatible, a low preparation temperature (<500 °C) for ferroelectric films is required. In this study, BiFeO3 films were successfully fabricated at a low annealing temperature (<450 °C) on aluminum foils by a metal-organic decomposition process. The effect of the annealing atmosphere on the performance of BiFeO3 films was assessed at 440 ± 5 °C. By using a N2-rich atmosphere, a large remnant polarization (Pr~78.1 μC/cm2 @ 1165.2 kV/cm), and a high rectangularity (~91.3% @ 1165.2 kV/cm) of the P-E loop, excellent charge-retaining ability of up to 1.0 × 103 s and outstanding fatigue resistance after 1.0 × 109 switching cycles could be observed. By adopting a N2-rich atmosphere and aluminum foil substrates, acceptable electrical properties (Pr~70 μC/cm2 @ 1118.1 kV/cm) of the BiFeO3 films were achieved at the very low annealing temperature of 365 ± 5 °C. These results offer a new approach for lowering the annealing temperature for integrated ferroelectrics in high-density FeRAM applications.

Superior dielectric energy storage performance of ultrafine-grained BNT-SBT solid-solution ceramics by solution combustion synthesis

The micrometer scale grain size and large remnant polarization of Bi0.5Na0.5TiO3 (BNT) ferroelectric ceramics severely constrain the breakdown strength and energy efficiency, respectively, restricting their energy storage application despite their large polarization. Hereby, superior energy storage performance is reported by a synergistic strategy of introducing Sr0.7Bi0.2TiO3 (SBT) relaxor ferroelectrics and a solution combustion synthesis (SCS) method. The BNT-SBT solid-solution ceramics are comparatively investigated by the two methods, conventional sintering (CS) and SCS. An ultrafine average grain size of ∼0.39 μm was obtained in the SCS-derived ceramic, and thus exhibits an ultra-high critical electric field of 548 kV/cm, and a high recoverable energy density of ∼5.69 J/cm3. Those key energy storage parameters are superior to those of the previous reported samples prepared by the CS method. Meanwhile, a high energy efficiency ∼90 %, a large power density of ∼130.44 MW/cm3 (at 320 kV/cm), and an ultrafast discharge time of ∼61.7 ns are also achieved. This study indicates that grain engineering combing with chemical design is an effective way to enhance the dielectric energy storage performance.

Enhanced energy-storage performances in lead-free ceramics via the Co-modulation by conduction effect and domain engineering

The main factors that limit the practical application of bismuth ferrite-based energy storage ceramics are their low breakdown electric field strength and large remnant polarization. Here, we achieve high energy storage behavior in (0.72-x)BiFeO3-0.28BaTiO3-xLa(Mg1/2Zr1/2)O3 (BF-BT-xLMZ) ferroelectric ceramics through directional defect modulation based on a transformation of the conductance mechanisms. The systematic experimental analysis coupled with the vacancy sink model suggests that the introduction of LMZ changes the trap-filled-limit conduction mode dominated by oxygen vacancy, leading to 4 times enhancement of the breakdown electric field in BF-BT-0.2LMZ. Meanwhile, the induced nanodomains create a size effect that effectively reduces the remnant polarization, resulting in an increase in efficiency by 3.5 times. As a result, the recoverable energy storage density of the ceramic reaches an outstanding 4.2 J/cm3, together with a high efficiency of 75.2%. This work provides a feasible strategy for the development of ferroelectric family in the field of high-energy storage.

Demonstration of 10 nm Ferroelectric Al0.7Sc0.3N-Based Capacitors for Enabling Selector-Free Memory Array.

In this work, 10 nm scandium-doped aluminum nitride (AlScN) capacitors are demonstrated for the construction of the selector-free memory array application. The 10 nm Al0.7Sc0.3N film deposited on an 8-inch silicon wafer with sputtering technology exhibits a large remnant polarization exceeding 100 µC/cm2 and a tight distribution of the coercive field, which is characterized by the positive-up-negative-down (PUND) method. As a result, the devices with lateral dimension of only 1.5 μm show a large memory window of over 250% and a low power consumption of ~40 pJ while maintaining a low disturbance rate of <2%. Additionally, the devices demonstrate stable multistate memory characteristics with a dedicated operation scheme. The back-end-of-line (BEOL)-compatible fabrication process, along with all these device performances, shows the potential of AlScN-based capacitors for the implementation of the high-density selector-free memory array.

Characteristics of NaNbO3 templates and improvement of electrical properties of textured KNLNS-BNKT ceramics

In this study, plate-like perovskite NaNbO3 (NN) templates were formed from Bi2.5Na3.5Nb5O18 (BiNN5) precursors via a molten salt method. The structure and microstructure of BiNN5 precursors and NN templates were studied. As a result, the platelike BiNN5 precursor particles have a bismuth layer perovskite structure, which is the basis for forming the synthesized plate-like NN particles that have a high aspect ratio with a width of 2-7 μm, a length of 5-12 μm and a thickness of 0.5-1 μm. From NN templates, we fabricated textured lead-free 0.98(K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3 − 0.02Bi0.5(Na0.4K0.1)TiO3 (KNLNS- BNKT) ceramic by the grain orientation technique. Experimental results show that the KNLNS-BNKT ceramics have a single-phase orthorhombic structure in which textured KNLNS-BNKT ceramics with 67% grain orientation. The electrical properties of the oriented ceramic are significantly improved compared to the non-oriented ceramic fabricated by the traditional method. Specifically, the electrical properties of the resulting KNLNS-BNKT oriented ceramics have a high dielectric constant (ε = 1323, an increase of 17%); large remnant polarization (Pr = 13.5 mC/cm2, an increase of 11.9%); high piezoelectric coefficient (d33 = 205 pC/N, an increase of 32%) and high electromechanical coupling coefficient (kp = 0.4, an increase of 11%).

Optimization of a LaNiO3 Bottom Electrode for Flexible Pb(Zr,Ti)O3 Film-Based Ferroelectric Random Access Memory Applications

The direct growth of ferroelectric films onto flexible substrates has garnered significant interest in the advancement of portable and wearable electronic devices. However, the search for an optimized bottom electrode that can provide a large and stable remnant polarization is still ongoing. In this study, we report the optimization of an oxide-based LaNiO3 (LNO) electrode for high-quality Pb(Zr0.52Ti0.48)O3 (PZT) thick films. The surface morphology and electrical conductivity of sol-gel-grown LNO films on a fluorophlogopite mica (F-mica) substrate were optimized at a crystallization temperature of 800 °C and a film thickness of 120 nm. Our approach represents the promising potential pairing between PZT and LNO electrodes. While LNO-coated F-mica maintains stable electrical conductivity during 1.0%-strain and 104-bending cycles, the upper PZT films exhibit a nearly square-like polarization–electric field behavior under those stress conditions. After 104 cycles at 0.5% strain, the remnant polarization shows decreases as small as ~14%. Under flat (bent) conditions, the value decreases to just 81% (49%) after 1010 fatigue cycles and to 96% (85%) after 105 s of a retention test, respectively.

Achieving excellent ferroelectric and dielectric performance of HfO2/ZrO2/HfO2 thin films under low operating voltage

Although the HfO2-based ferroelectric thin films are compatible with the complementary metal-oxide-semiconductor (CMOS) technology and exhibit excellent scalability, they still suffer from low dielectric tunability, metastable ferroelectric orthorhombic phase and poor endurance. Here, we fabricated the HfO2/ZrO2/HfO2 sandwich structured thin films via atomic layer deposition process as well as the influence of voltage cycling, Hf/Zr ratios and annealing temperature on ferroelectricity and dielectric tunability of them was investigated systematically. At pristine states, the antiferroelectric-like behavior of polarization-voltage hysteresis loops become more and more obvious with the decrement of ZrO2 content in the middle layers. After waking-up, the large remnant polarization (2Pr, ∼43 μC/cm2) and high dielectric tunability (∼51 %) can be achieved under low operating voltage of 2.5 V. Noting that the 2Pr is still higher than 40 μC/cm2 and the dielectric tunability remains about 50 % after 109 cycles. In addition, the HfO2/ZrO2/HfO2 thin films also exhibited high energy storage properties with the total energy storage density of ∼62 J/cm3 and the recoverable energy storage density of ∼32 J/cm3. These results indicated that the strategy of sandwich structure design is beneficial to promoting the development of electronic devices towards miniaturization, integrated, and multifunction along with high performance and reliability.

Phase structure, dielectric and energy storage properties of Na0.5Bi0.5TiO3-BaTiO3 ceramics with Bi(Mg2/3Nb1/3)O3 modification

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications owing to their individual crystal structure and phase transition information. However, the high coercive field (EC) and large remnant polarization (Pr) are detrimental for practical applications. In this work, the composition-dependent phase structure, micromorphology, dielectric and energy storage properties of (1-x)(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-xBi(Mg2/3Nb1/3)O3 (NBBT-100xBMN, x = 0.18, 0.20, 0.22 and 0.25) ternary ceramics were hereby investigated. The addition of BMN facilitates the phase transformation from rhombohedral (R3c) to tetragonal (P4bm), which is beneficial for the enhancement of relaxation behavior, and meanwhile impels the grain growth. Combined with the influence of grain size on breakdown field strength, an optimal recoverable energy storage density (Wrec) of 1.88 J/cm3 with a high energy storage efficiency (η) of 82.15% was achieved in the NBBT-20BMN ceramic composition under the dielectric breakdown strength (DBS) of 150 kV/cm, accompanied by the excellent temperature stability from room temperature to 200 °C. All these manifest that the NBBT-20BMN ceramics have an attractive application prospect in the energy storage field.

Phase-Transition Induced Optimization of Energy Storage and Temperature Stability of NaNbO3 Doped BNBST Ceramics

The 0.5Bi0.5Na0.5TiO3−0.5Ba0.3Sr0.7TiO3 (BNBST) ceramic is a relatively good relaxation component with tripartite phase and tetragonal phase coexisting at room temperature. Tripartite R3c is a polar phase, which can transform to long range ordered ferroelectric structures under the action of an applied electric field, exhibiting large remnant polarization (P r), which limits its application in energy storage. In this work, we designed NaNbO3 (NN) modified Bi0.5Na0.5TiO3-Ba0.3Sr0.7TiO3 ceramics to prepare (1−x) (0.5Bi0.5Na0.5TiO3−0.5Ba0.3Sr0.7TiO3)−xNaNbO3 (abbreviated as (1−x)BNBST-Xnn, x = 0, 0.05, 0.10, 0.15, 0.20, 0.25) relaxor ferroelectrics. By increasing the NN amount, the phase composition is regulated to induce the transformation of the polar phase R3c to the weakly polar phase P4bm, leading to a smaller P r. The ferroelectric test results show that the ceramic sample with x = 0.1 achieves a high effective energy storage density (W rec = 2.58 J cm−3) and energy storage efficiency (ƞ = 91%) at 140 kV cm−1.

Large remnant polarization and improved dielectric, magnetic properties of Te-modified 0.7BiFeO3–0.3BaTiO3 ceramics

BiFeO3–BaTiO3 (BF–BT) ceramics, as a kind of binary ferroelectric material with excellent properties, have a wide range of applications. A novel Te-doped 0.7BiFe1−xTexO3–0.3BaTiO3 (x = 0–0.07) ceramics with enhanced ferroelectric properties were designed and synthesized via a solid-phase reaction. Results of X-ray diffraction and Rietveld refinement revealed a phase transition from the rhombohedra and tetragonal phases to a single tetragonal phase with increasing Te content, indicating the formation of a morphotropic phase boundary (MPB) in samples with x = 0–0.03. The fitting results of the X-ray photoelectron spectra showed that the Te introduction reduced the Fe2+ concentration and improved the insulating performance. Due to the Te-induced structure distortion of the rhombohedral phase and tetragonal phase, a large remnant polarization of 51 μC/cm2 is obtained at x = 0.01, which is superior to those reported in many studies on BF–BT bulk materials. The dielectric properties revealed that Te addition effectively adjusted the relaxation degree of the ceramics, showing an ideal relaxor ferroelectric behavior in samples with x = 0.05 and 0.07. Additionally, Te substitution reduced the Fe–O–Fe bond angle and the grain size, achieving enhanced ferromagnetism and affording the largest remnant magnetization in the case of x = 0.03, which is around six times that of the pure BF–BT ceramic.

Large ferroelectric polarization of pure xBiFeO3-(1−x)BaTiO3 solid solution ceramics synthesized by microwave sintering

BiFeO3-BaTiO3 (BFO-BTO)-based lead-free electroceramics have long been synthesized using the microwave sintering approach, but the resulting multiferroic performance has not been excellent. In this work, we report an attempt to achieve competitive ferroelectric properties in microwave-sintered xBFO-(1–x)BTO (x = 0.6–0.8) ceramics. Adopting a sintering process with a short dwell time of 30 min at 970 °C, we obtain high-quality ceramics with a high density, pure perovskite structure, uniform element distribution, and coarse grains. Furthermore, the fabricated ceramics can reproduce the typical characteristics of pure BFO-BTO, including a morphotropic phase boundary (MPB), relaxor ferroelectric behavior, weak ferromagnetism, and enhanced ferroelectricity near the MPB. More remarkably, a large intrinsic remnant polarization Pr as high as ∼28 μC/cm2 is achieved by combing the MPB-enhanced ferroelectricity and the advantages of microwave synthesis. The maximal Pr accomplished here is competitive with that of the same bulk solid solution obtained via other fabrication approaches. Our study illustrates that microwave synthesis is a powerful approach with which to prepare high-performance BFO-BTO-based ceramics.

The Influence of BaTiO3 Content on the Energy Storage Properties of Bi0.5Na0.5TiO3-Bi(Mg2/3Nb1/3)O3 Lead-Free Ceramics

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO3 (BT) was introduced to the 0.94Na0.5Bi0.5TiO3-0.06Bi(Mg2/3Nb1/3)O3 system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na0.5Bi0.51TiO3-xBaTiO3]-0.06Bi(Mg2/3Nb1/3)O3 (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum Pmax (38.29 μC/cm2) and Eb (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of Wrec ~ 1.02 J/cm3 and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications.

Semiconducting nonperovskite ferroelectric oxynitride designed ab initio

The recent discovery of HfO2-based and nitride-based ferroelectrics that are compatible to the semiconductor manufacturing process has revitalized the field of ferroelectric-based nanoelectronics. Guided by a simple design principle of charge compensation and density functional theory calculations, we discover that HfO2-like mixed-anion materials, TaON and NbON, can crystallize in the polar Pca 2 1 phase with a strong thermodynamic driving force to adopt anion ordering spontaneously. Both oxynitrides possess large remnant polarization, low switching barriers, and unconventional negative piezoelectric effect, making them promising piezoelectrics and ferroelectrics. Distinct from HfO2 that has a wide bandgap, both TaON and NbON can absorb visible light and have high charge carrier mobilities, suitable for ferroelectric photovoltaic and photocatalytic applications. This class of multifunctional nonperovskite oxynitride containing economical and environmentally benign elements offers a platform to design and optimize high-performing ferroelectric semiconductors for integrated systems.

Structural Engineering of H0.5Z0.5O2‐Based Ferroelectric Tunneling Junction for Fast‐Speed and Low‐Power Artificial Synapses

AbstractAdvanced synaptic devices capable of neuromorphic data processing are widely studied as the building block in the next‐generation computing architecture for artificial intelligence applications. Due to its fast speed, low power, and excellent complementary metal‐oxide‐semiconductor (CMOS) compatibility, Zr‐doped HfO2 (HZO)‐based ferroelectric tunnel junction (FTJ) are promising candidates as a new type of non‐volatile memory for neuromorphic device applications. Here, an experimental approach is reported to enhance the tunneling efficiency and the electrical performance by engineering the dielectric stack of the FTJ device. By sandwiching the HZO ferroelectric layer with ZrO2 and Al2O3 layers, the FTJ tunneling current is greatly increased with lowered barrier, larger remnant polarization (Pr), and tunneling electrical resistance ratio as well as suppressed leakage current have been achieved. The optimized FTJ devices are further implemented emulating synaptic functions with demonstrated short/long‐term synaptic plasticity and spike‐timing‐dependent plasticity behaviors. Such engineering in HZO‐based FTJ devices can be promising and instructive for the realization of future ultra‐low‐power and CMOS‐compatible neuromorphic devices and systems.

Phase evolution and enhanced room temperature piezoelectric properties response of lead-free Ru-doped BaTiO3 ceramic

Abstract Recent years have witnessed considerable work on the development of lead-free piezoelectric ceramic materials and their structure–property correlations. The development of piezo response is a strong function of phase evolution in these materials. In this work, we report the effect of Ru doping and consequent phase evolution on the maximization of piezoelectric response of polycrystalline lead-free barium titanate, depicted as Ba(RuxTi1-x)O3 (BRT). The samples were prepared in a narrow compositional range of 0 ≤ x ≤ 0.03 using the conventional solid-state reaction method. Ru doping increases the leakage current of BaTiO3 samples attributed to increased oxygen vacancy concentration due to substitution of Ti4+ by Ru3+. Detailed structural analysis reveals that samples exhibiting coexistence of tetragonal (space group: P4mm) and orthorhombic (space group: Amm2) structured phases near room temperature reveal relatively enhanced piezoelectric properties. The BRT sample with Ru content of 2 mol% yields a maximum longitudinal piezoelectric coefficient, d33 of ∼269 pC/N, a high strain value of 0.16% with a large remnant polarization of ∼19 µC/cm2 and a coercive field of 5.8 kV/cm. We propose that the ‘4d’ orbital of Ruthenium plays a crucial role in improving the functional properties and in decreasing the ferroelectric Curie temperature. Our work provides clues into tailoring the phase evolution for designing lead-free piezoelectric materials with enhanced piezoelectric properties.

Giant power density from BiFeO3-based ferroelectric ceramics by shock compression

Ferroelectric pulsed-power sources with rapid response time and high output energy are widely applied in the defense industry and mining areas. As the core materials, ferroelectric materials with large remnant polarization and high electrical breakdown field should generate high power under compression. Currently, lead zirconate titanate 95/5 ferroelectric ceramics dominated in this area. Due to environmental damage and limited output power of lead-based materials, lead-free ferroelectrics are highly desirable. Here, the electrical response of 0.9BiFeO3-0.1BaTiO3 (BFO-BT) ferroelectric ceramics under shock-wave compression was reported, and a record-high power density of 4.21 × 108 W/kg was obtained, which was much higher than any existing lead-based ceramics and other available energy storage materials. By in situ high-pressure neutron diffraction, the mechanism of shock-induced depolarization of the BFO-BT ceramics was attributed to pressure-induced structural transformation, and the excellent performance was further elaborated by analyzing magnetic structure parameters under high pressures. This work provides a high-performance alternative to lead-based ferroelectrics and guidance for the further development of new materials.

Large remnant polarization and great reliability characteristics in W/HZO/W ferroelectric capacitors

In this work, the effect of rapid thermal annealing (RTA) temperature on the ferroelectric polarization in zirconium-doped hafnium oxide (HZO) was studied. To maximize remnant polarization (2Pr), in-plane tensile stress was induced by tungsten electrodes under optimal RTA temperatures. We observed an increase in 2Pr with RTA temperature, likely due to an increased proportion of the polar ferroelectric phase in HZO. The HZO capacitors annealed at 400°C did not exhibit any ferroelectric behavior, whereas the HZO capacitors annealed at 800°C became highly leaky and shorted for voltages above 1 V. On the other hand, annealing at 700 °C produced HZO capacitors with a record-high 2Pr of ∼ 64 μC cm−2 at a relatively high frequency of 111 kHz. These ferroelectric capacitors have also demonstrated impressive endurance and retention characteristics, which will greatly benefit neuromorphic computing applications.