Large Polarization Value Research Articles

2D Molecular Ferroelectric with Large Out‐of‐plane Polarization for In‐Memory Computing

Abstract2D ferroelectric materials with out‐of‐plane polarization are crucial for future nanoscale logic devices due to the increasing demand for energy‐efficient architectures in artificial intelligence. However, only a few 2D out‐of‐plane ferroelectrics are confirmed experimentally. As an important branch of ferroelectrics, organic–inorganic hybrid perovskite ferroelectrics show flexible structures, making them eligible for constructing multifunctional materials. Here, a 2D organic–inorganic hybrid perovskite ferroelectric (6‐BHA)2CdBr4 (6‐BHA is 6‐bromohexylamine) is designed, which crystallizes in polar point group Cc. It experiences the reversal phase transition at 317.8 K and possesses multiaxial ferroelectric properties. More interestingly, it exhibits a large spontaneous polarization value of 3.26 µC cm−2 in out‐of‐plane direction of the film compared with typical 2D ferroelectrics. Moreover, an inverter based on (6‐BHA)2CdBr4 is fabricated, which serves as a proof of concept for the feasibility for logic‐in‐memory devices. This work not only enriches the family of molecular ferroelectrics but also shows the potential to create the next generation of in‐memory computing devices, nanoelectronics devices, and ultra‐high‐density memories.

Reliable Accessibility of Intermediate Polarization States in Textured Ferroelectric Al0.66Sc0.34N Thin Film

AbstractFerroelectric materials are promising candidates for neuromorphic computing synaptic devices due to the nonvolatile multiplicity of spontaneous polarization. To ensure a sufficient memory window, ferroelectric materials with a large coercivity are urgently required for practical applications in highly scaled multi‐bit memory devices. Herein, a remarkable reliability of intermediate ferroelectric polarization states is demonstrated in a textured Al0.66Sc0.34N thin film with a coercive field of 2.4 MV cm−1. Al0.66Sc0.34N thin films are prepared at 300 °C on Pt (111)/Ti/SiO2/Si substrates using a radio frequency reactive sputtering method. Al0.66Sc0.34N thin films exhibit viable ferroelectricity with a large remanent polarization value of >100 µC cm−2. Through the conventional current–voltage characteristics, polarization switching kinetics, and temperature dependence of coercivity, the reproducibility of multiple polarization states with apparent accuracy is attributed to a small critical volume (3.7 × 10−28 m3) and a large activation energy (3.3 × 1027 eV m−3) for nucleation of the ferroelectric domain. This study demonstrates the potential of ferroelectric Al1‐xScxN for synaptic weight elements in neural network hardware.

Achieving large energy density and high efficiency in (Bi0.5Na0.5)0.7Sr0.3TiO3–Ba(Mg1/3Sb2/3)O3 ceramic

Recently, due to ultra-high energy density and exceptionally fast discharge time, high-performance dielectric capacitors have become a research hotspot in electric pulse power equipment. However, it is challenging to achieve a hige energy storage density and efficiency of ceramic worked in the area for capacitors. Herein, novel (1-x) (Bi0.5Na0.5)0.7Sr0.3TiO3-xBa(Mg1/3Sb2/3)O3 (xBMS, x = 0.08, x = 0.10, x = 0.12, x = 0.14) dielectric ceramics were prepared by a solid state reaction method. 0.10BMS ceramic has a large maximum polarization value of 37.1 μC/cm2 at 330 kV/cm, which achieves a high energy storage density of 4.42 J/cm3 and ultra-high efficiency of 93 %. Meanwhile, 0.10BMS ceramic has great energy storagy stability in the temperature range of 40–140 °C and the frequency range of 4–200 Hz. In addition, the sample also shows an fast t0.9 of 60.8 ns, high CD of 806.8 A cm−2, and PD of 48.41 MW/cm3. Therefore, 0.10BMS ceramic has potential application prospects in electronic devices.

Improvement of the energy storage performance in Pb0.88La0.12ZrO3 thin films by inserting ZrO2 layer

A method for significantly enhancing the breakdown field strength and energy storage density of Pb0.88La0.12ZrO3 (PLZ) films by inserting ZrO2 (ZO) layer is provided. PLZ films with the inserting layer of ZrO2 were deposited on SiO2/Si substrates buffered with LaNiO3 films by the sol-gel method. The effect of ZrO2 precursor solution concentration on structure and electrical properties was investigated. The results show that for the composite films with the sandwich structure, much improved electrical breakdown strength values of 1543 kV/cm and maximum polarization values of 83.5 μC/cm2 were obtained, which are 141% and 40% higher than pure PLZ films, respectively. With the combination of a high breakdown field strength and a large maximum polarization value, the film has an energy storage density of up to 32.6 J/cm3 when ZrO2 precursor solution concentration is 0.1 mol/L. Our results show that the design of PLZ/ZO/PLZ composite films is an effective way to obtain high energy storage density capacitors.

Remarkably minimized domain and elevated energy storage properties in Na0.48Bi0.48Ba0.04TiO3-based relaxor antiferroelectrics by interposing Bi(Mg2/3Ta1/3)O3

Lead-free dielectric capacitors have been embraced recently due to their tiny volume, large energy density and superfast charge–discharge speed. Here, a recoverable energy storage density of ∼ 10.73 J cm−3 and an efficiency of ∼ 80.5% were simultaneously revealed in traditional sintering (1 − x) (Na0.48Bi0.48Ba0.04TiO3)-xBi(Mg2/3Ta1/3)O3 (x = 0.16) ceramics (BNBT-0.16BMT) under an applied electric field of 540 kV cm−1 via disordering B-site ions and modifying the B-site cation ratio. Specifically, the disorder of B-site ions was found to alter the crystal structure, delaying maximum polarization. Phase switching between rhombohedral and tetragonal was characterized with transmission electron microscopy, Raman scattering and dielectric constant curves. Mg/Ta dopant was shown to cause electric charge mismatch and change dielectric anomaly peaks, leading to a large maximum polarization value. Finally, BNBT-0.16BMT stabilizes the relaxor antiferroelectrics (RAFE) system, with a significant broad frequency (0.5–120 Hz), broad temperature stability (20–160 °C), and excellent discharge performance (WD ∼ 5.23 J cm−3; Ea ∼ 350 kV cm−1). This preparation shows potential for broad application in dielectric capacitors.

AgNbO3-based antiferroelectric ceramics with superior energy storage performance via Gd/Ta substitution at A/B sites

Dielectric materials have attracted considerable attention owing to their excellent power densities and fast charge/discharge characteristics. AgNbO3, as a typical antiferroelectric (AFE) material, is regarded as a promising dielectric material owing to its large polarization value and environmentally friendly nature. However, the low energy density of this system limits its further application. In this study, the slim P-E loops are implemented by Gd/Ta substitution at A/B sites, which provide a superior energy storage performance with a Wrec of 6.99 J/cm3 under 400 kV/cm. This improvement in energy storage property can be attributed to three factors: firstly, a significant improvement in the AFE stability is obtained by reducing the tolerance factor t and the B-site polarizability; secondly, this strategy leads to a reduction in the grain size of the material, optimizing the breakdown electric field Eb of AN-based ceramics; lastly, A/B-site codoping induces structural distortion of the material, constructs an internal chemical pressure, and suppresses its oxide octahedral tilting. Furthermore, the Gd/Ta co-doped ceramics exhibit an excellent practical charging/discharging efficiency (＜10 μs). This work demonstrates that the electrical properties of AN-based ceramics have been optimized by Gd/Ta codoping, making them good candidates for pulsed power systems.

On the atomistic origin of the polymorphism and the dielectric physical properties of beryllium oxide.

Polymorphic beryllium oxide has been theoretically investigated from first principles as regards orbital occupancies, chemical bonding, polarization, as well as dielectric properties. By means of Crystal-Orbital Bond Index (COBI) analysis, the important role of the 2p orbitals on beryllium has been elucidated, in particular in terms of the correlation between polarization and beryllium-atom displacement, including the impact of the latter on the covalency of the BeO bond. In addition, several structural possibilities for a Bex Mg1-x O solid solution have been investigated for a Be content between 6% and 22%; for those, dynamically stable structures have been found, displaying large polarization values, more covalent BeO bonds, and a tendency for tetrahedral Be coordination. The dynamically unstable structures, however, resemble rock-salt BeO in their local structural properties around the Be atom. High dielectric constants and band gaps indicating insulating behavior have been found for those.

Influence of Polymorphism on the Electrochemical Behavior of Dilithium (2,3-Dilithium-oxy)-terephthalate vs. Li

Organic electrode materials offer obvious opportunities to promote cost-effective and environmentally friendly rechargeable batteries. Over the last decade, tremendous progress has been made thanks to the use of molecular engineering focused on the tailoring of redox-active organic moieties. However, the electrochemical performance of organic host structures relies also on the crystal packing, like the inorganic counterparts, which calls for further efforts in terms of crystal chemistry to make a robust redox-active organic center electrochemically efficient in the solid state. Following our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on the impact of polymorphism on the electrochemical behavior of dilithium (2,3-dilithium-oxy-)terephthalate vs. Li. Having isolated dilithium (3-hydroxy-2-lithium-oxy)terephthalate through an incomplete acid-base neutralization reaction, its subsequent thermally induced decarboxylation mechanism led to the formation of a new polymorph of dilithium (2,3-dilithium-oxy-)terephthalate referred to as Li4-o-DHT (β-phase). This new phase is able to operate at 3.1 V vs. Li+/Li, which corresponds to a positive potential shift of +250 mV compared to the other polymorph formerly reported. Nevertheless, the overall electrochemical process characterized by a sluggish biphasic transition is impeded by a large polarization value limiting the recovered capacity upon cycling.

Chiral Zn‐Based Organic‐Inorganic Hybrid Ferroelectrics with Large Polarization and Luminescence

AbstractMulti‐functionalized lead‐free organic‐inorganic hybrid ferroelectrics have recently realized diverse applications especially for optoelectronics and photovoltaics. Herein, the chiral Zn‐based organic−inorganic hybrids are discovered: [(R)‐(−)‐2‐methylpiperazine‐1,4‐diium][Zn(H2O)6]•(SO4)2 (RMPZnS2, space group P21) and [(S)‐(+)‐2‐methylpiperazine‐1,4‐diium]2[Zn(H2O)6]•(SO4)3 (SMP2ZnS3, space group P21212). Through experimental and computational investigations, it is found that RMPZnS2 is a ferroelectric with considerable large polarization value (P ≈ 9.5 µC cm−2) along b–axis, and its ferroelectric‐paraelectric phase transition is switched by rotation of organic cations. Meanwhile, it also possesses a fascinating photovoltaic effect driven by the polar charges at solar‐blind UV region, endowing it with the potential of self‐driven photodetection. In addition, white‐light emissions of the RMPZnS2 and SMP2ZnS3 are observed. The enhanced luminescence by heating is especially suitable for the application in white light‐emitting diodes. Overall, these chiral emission ferroelectrics at the supramolecular level will largely expand their applications in multidisciplinary fields.

Optimization of Anisotropic Crystalline Structure of Molecular Necklace-like Polyrotaxane for Tough Piezoelectric Elastomer.

While piezoelectric materials are applied in various fields, they generally exhibit poor mechanical toughness. To increase the applicability of these, their mechanical properties need to be improved. In this study, a tough piezoelectric polyrotaxane (PRX) elastomer was developed by blending PRX samples of two different lengths, formed using 10K and 35K poly(ethylene glycol), to align dipole moments for optimization of the piezoelectricity characteristics. The effects of the blending ratio on the crystalline structure of the obtained PRX elastomer were investigated by X-ray diffraction analysis and transmission electron microscopy. In addition, the ferroelectric and piezoelectric properties of the PRX elastomer were evaluated based on its polarization hysteresis loop and voltage generation characteristics, respectively. The PRX elastomer formed by using a ratio of 3:1 (ePR10k7535k25) exhibited a long-range-ordered anisotropic crystalline structure, resulting in a large polarization (Pr) value. As a result, ePR10k7535k25 showed greatly enhanced piezosensitivity against the mechanical vibrations generated by respiratory signals.

Interface control of tetragonal ferroelectric phase in ultrathin Si-doped HfO2 epitaxial films

Nanoscaled HfO2-based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is that the ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics when the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO2 on YSZ[001]/[110]/[111] substrates. The deposited films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axes of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and can be reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which can easily exploit the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO2-based ferroelectric materials.

Giant optical absorption and ferroelectric polarization of BiCoO2S perovskite oxysulfide by first principles prediction.

Obtaining an ideal ferroelectric photovoltaic (FE-PV) material with a narrow bandgap and a large ferroelectric polarization value can enable us to achieve great practical FE-PV performance. By the introduction of sulfur into the tetragonal BiCoO3 perovskite with a C-type antiferromagnetic ordering, it is found that the bandgap of BiCoO2S decreases significantly (about 1.2 eV) while maintaining a large polarization value (about 1.86 C m-2) that is similar to the value of 1.793 C m-2 of BiCoO3. Most noteworthy is that the optical absorption of BiCoO2S is remarkably higher than those of BiCoO3 and other FE-PV materials. The decrease of the BiCoO2S bandgap originates from the movement of Co 3d states to a low-energy position due to the reduction of the Co ionicity when the less electronegative sulfur is introduced into BiCoO3 to substitute oxygen. The narrow bandgap and the high optical absorption of the BiCoO2S films grown on different substrates are favorable for FE-PV applications. In addition, the bandgap of BiCoO2S can be modulated by the doping amount of sulfur, which can help us fabricate multilayer FE-PV devices based on different bandgaps from different layers.

Interface Control of Tetragonal Ferroelectric Phase in Ultrathin Si-Doped HfO <sub>2</sub> Epitaxial Films

Nanoscaled HfO2-based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics as the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO2 on YSZ[001]/[110]/[111] substrates. The films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axis of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and are reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which easily exploiting the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO2-based ferroelectric materials.

Tunable multiferroic order parameters in Sr1−xBaxMn1−yTiyO3

Responding to the rapidly increasing demand for efficient energy usage and increased speed and functionality of electronic and spintronic devices, multiferroic oxides have recently emerged as key materials capable of tackling this multifaceted challenge. In this paper, we describe the development of single-site manganese-based multiferroic perovskite materials with modest amounts of nonmagnetic Ti substituted at the magnetic Mn site in Sr1- x Ba x Mn1- y Ti y O3 (SBMTO). Significantly enhanced properties were achieved with ferroelectric-type structural transition temperatures boosted to ∼430K. Ferroelectric distortions with large spontaneous polarization values of ∼30μC/cm2, derived from a point charge model, are similar in magnitude to those of the prototypical nonmagnetic BaTiO3. Temperature dependence of the system's properties was investigated by synchrotron x-ray powder diffraction and neutron powder diffraction at ambient and high pressures. Various relationships were determined between the structural and magnetic properties, Ba and Ti contents, and T N and T C. Most importantly, our results demonstrate the large coupling between the magnetic and ferroelectric order parameters and the wide tunability of this coupling by slight variations of the material's stoichiometry.

Reduced leakage current, enhanced ferroelectric and dielectric properties in Mn-doped BiFeO3 thin film composited with TiO2 layers

Abstract The 2 mol% Mn-doped Bi1.05FeO3 (abbreviated as BFOMn, S0), BFOMn composited films with TiO2 layer at the surface of BFOMn (S1), and on the interface between BFOMn film and substrate (S2), as well as at the both sides of the BFOMn film (S3) were prepared on indium tin oxide (ITO)/glass substrates through a chemical solution deposition process. The effects of TiO2 layers deposited at different positions on microstructure, insulating, ferroelectric and dielectric performances are fully investigated. The crystallized perovskite structures without any secondary phases are well maintained in all samples. Increased grain sizes can be achieved with the introduction of TiO2. Among these films, S3 has large average grain size and possesses decreased leakage current density of 7.2 × 10−5 A/cm2 under 400 kV/cm, relatively large remanent polarization (Pr) value of 82.3 μC/cm2 under 3333 kV/cm at 10 kHz, larger dielectric constant (∼ 330) and smaller dissipation factor (∼ 0.04) at 100 kHz. These results demonstrate that introducing TiO2 layers into appropriate positions can be a feasible way to improve the microstructure and enhance the electrical properties of BFO-based films.

Energy storage properties in BaTiO3-Bi3.25La0.75Ti3O12 thin films

Developing lead-free film dielectric capacitors with high-performance of energy storage density, efficiency, fatigue endurance, and thermal stabilities is desirable. Here, we report energy storage properties in (1-x)BaTiO3-xBi3.25La0.75Ti3O12 thin films. It is revealed that a 0.6BaTiO3-0.4Bi3.25La0.75Ti3O12 thin film with a thickness of 280 nm and a crystallization temperature of 650 °C shows a breakdown strength of 3.23 MV/cm with a large polarization value and dielectric constant. An ultrahigh energy storage density of 61.1 J/cm3 and an efficiency of 84.2% are simultaneously achieved at room temperature. Additionally, excellent fatigue endurance after 6 × 109 cycles and good thermal stability up to 150 °C are observed, implying excellent energy storage performance in 0.6BaTiO3-0.4Bi3.25La0.75Ti3O12 thin films.

A rhombohedral ferroelectric phase in epitaxially strained Hf0.5Zr0.5O2 thin films.

Hafnia-based thin films are a favoured candidate for the integration of robust ferroelectricity at the nanoscale into next-generation memory and logic devices. This is because their ferroelectric polarization becomes more robust as the size is reduced, exposing a type of ferroelectricity whose mechanism still remains to be understood. Thin films with increased crystal quality are therefore needed. We report the epitaxial growth of Hf0.5Zr0.5O2 thin films on (001)-oriented La0.7Sr0.3MnO3/SrTiO3 substrates. The films, which are under epitaxial compressive strain and predominantly (111)-oriented, display large ferroelectric polarization values up to 34 μC cm-2 and do not need wake-up cycling. Structural characterization reveals a rhombohedral phase, different from the commonly reported polar orthorhombic phase. This finding, in conjunction with density functional theory calculations, allows us to propose a compelling model for the formation of the ferroelectric phase. In addition, these results point towards thin films of simple oxides as a vastly unexplored class of nanoscale ferroelectrics.

Reduced leakage current, enhanced energy storage and dielectric properties in (Ce,Mn)-codoped Ba0.6Sr0.4TiO3 thin film

Ba0.6Sr0.4TiO3, Ce-doped Ba0.6Sr0.4TiO3, Mn-doped Ba0.6Sr0.4TiO3, (Ce,Mn) co-doped Ba0.6Sr0.4TiO3 (abbreviated as BST, BSTCe, BSTMn, BSTCeMn) thin films were deposited on LaNiO3(LNO)/Si substrates. The effects of ion doping on the microstructure and electrical properties of BST-based thin film have been researched and discussed. The X-ray diffraction pattern shows that each sample has pure perovskite phase structure with high (l00) peaks. The microstructure of each film is quite dense with uniform size. Compared with pure BST, improved insulating properties can be found in ion-doped BST thin films. For all the films, Ohmic conduction, space charge limited conduction and interface-limited Fowler-Nordheim tunneling should be the main conduction mechanisms within different electric field regions. For the case of BSTCeMn thin film, it possesses enhanced energy storage performance with a recoverable energy storage density (18.01 J/cm3) and a energy storage efficiency (75.1%) under 2000 kV/cm. This can be closely related to the small remanent polarization value (Pr= 1.89 μC/cm2), large maximum polarization value (Pmax= 28.08 μC/cm2) as well as big maximum electric field (2000 kV/cm). Also, it exhibits a large dielectric constant of 405 and a small dissipation factor of 0.075 at 500 kHz.

Thickness-dependent ferroelectric and dielectric behaviors for Ni-doped Na0.05Bi0.05TiO3 film derived by chemical solution deposition

Na0.05Bi0.05(1+0.03)Ti0.97Ni0.03O3 (NBTNi) thin films with thickness within the range of 250 ~ 880 nm were grown on indium tin oxide (ITO)/glass substrates via a chemical solution deposition method. The thickness impacts on the microstructure, insulating, ferroelectric and dielectric characteristics were investigated. Single perovskite structure in each film is observed from X-ray diffraction. Compared with the other films, the 880 nm-thick NBTNi film has elevated ferroelectric properties with a large remanent polarization (P r ) value of 20.2 μC/cm2 due to the decreased leakage current density resulting from the increasing thickness as well as the large grain size. Moreover, the NBTNi film of 880 nm possesses enhanced energy storage performance with a relatively high energy-storage density value of 45.1 J/cm3 and energy-storage efficiency of 37%. Also, a large dielectric tunability value of 25.4% can be obtained at 500 kV/cm and 50 kHz. In addition, the dielectric constant and dissipation factor of the NBTNi film with thickness of 880 nm are 450 and 0.02 at 50 kHz, respectively.

A Fluid Liquid-Crystal Material with Highly Polar Order.

An anomalously large dielectric permittivity of ≈104 is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid-crystal compound having a 1,3-dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X-ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 µC cm-2 , and a parallelogram-shaped polarization-electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field-induced polarization switching occurs. Furthermore, sufficiently larger second-harmonic generation is observed for DIO in the MP phase. Second-harmonic-generation interferometry clearly shows that the sense of polarization is inverted when the +/- sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric-like parallel polar arrangement of the molecules is generated along the director in the MP phase.