Spontaneous Ferroelectric Polarization Research Articles

Tunable Ferroionic Properties in CeO2/BaTiO3 Heterostructures.

Ferroionic materials combine ferroelectric properties and spontaneous polarization with ionic phenomena of fast charge recombination and electrodic functionalities. In this paper, we propose the concept of tunable polarization in CeO2-δ (ceria) thin (5 nm) films induced by built-in remnant polarization of a BaTiO3 (BTO) ferroelectric thin film interface, which is buried under the ceria layer. Upward and downward fixed polarizations at the BTO thin film (10 nm) are achieved by the lattice termination engineering of the SrO or TiO2 terminated Nb:SrTiO3 (NSTO or STN) substrate. We find that the ceria layer punctually replicates the polarization of the BTO interface via a dynamic reconfiguration of its intrinsic defects, i.e., oxygen vacancies and small polarons. Tunable oxidative or reducing properties (redox) also arise at the surface from the built-in polarization. Opposite polarities at the ceria termination tune the chemo-physical dynamics toward water molecule adsorbates. The inversion of the surface potential leads to a modulation of the water adsorption-desorption equilibrium and water ionization (splitting) redox overpotentials within ±400 mV at room temperature, depending on the ceria termination's charges. Such tunability opens up the perspectives of using ferroionics for wireless electrochemically enhanced catalysis.

Ferroelectric polarization synergism boosting CdS/PbTiO3 S-scheme heterostructures for efficiently bifunctional environmental applications

It is of great significance and challenges to construct physical field-enhanced photocatalysts for energy and environmental applications. Herein, an artificial-photosynthesized CdS/PbTiO3 S-scheme heterostructures with the enhancement of polarization electric field have been developed to promote the bifunctionally catalytic efficiencies for Cr(VI) photoreduction degradation of heavy metal pollution and Tetracycline (TC) photooxidation degradation of antibiotic. In our work, CdS nanoparticles are selectively grown on the positive polarization planes of PbTiO3 microplates to form the same direction for both the ferroelectric polarization field of PbTiO3 and the built-in electric field of S-scheme heterojunction. In this case, the stable heterostructures of PTO(00−1)/CdS(010) are obtained, and the greatly improved photocatalytic performances of redox degradation are achieved. The charge transfer mechanism and the synergetic effect between the spontaneous ferroelectric polarization and S-scheme heterojunction have been revealed by DFT calculations and experimental verifications. This interesting finding provides new insight into the design of efficient artificial-photosynthesized photocatalytic systems and we hope our work could serve as a valuable reference for our colleagues.

2D perovskite Ca2Nb3O10 nanosheet featuring Berry curvature dipole and canted persistent spin texture reversible with in-plane ferroelectricity

Two-dimensional materials can result in rich and unique electronic features through symmetry breaking. A wide band gap 2D perovskite Ca2Nb3O10 (CNO) nanosheet is investigated for exotic electronic or spin-related properties using state-of-the-art first-principles calculations. The CNO nanosheet exhibits spontaneous in-plane ferroelectric polarization confined in the y direction owing to the low symmetry of the crystal structure. A canted persistent spin texture (PST) can be observed in spin-split bands, which depict a unidirectional spin configuration tilted along the yz-plane. A correlation between the canted PST and ferroelectricity has been found, as in-plane ferroelectric switching can successfully reverse the typical PST. The nonvanishing Berry curvature dipole (BCD) resulting from the interplay of spin–orbit coupling (SOC) and inversion symmetry breaking is also reversible with in-plane ferroelectric polarization. Therefore, the possibility of fully electrically adjustable canted PST and BCD in a 2D perovskite CNO nanosheet provides a pathway toward creating affordable, non-volatile spintronic devices.

A Lead-Free Ferroelectric 2D Dion-Jacobson Tin Iodide Perovskite.

2D hybrid organic-inorganic halide perovskites emerge as a new class of 2D semiconductors with the potential to combine excellent optoelectronic properties with symmetry-enabled properties such as ferroelectricity. Although many lead-based ferroelectric 2D halide perovskites are reported, there is yet to be a conclusive report of ferroelectricity in tin-based 2D perovskites. Here, the structures and properties of a new series of 2D Dion-Jacobson (DJ) Sn perovskites: (4AMP)SnI4, (4AMP)(MA)Sn2I7, and (4AMP)(FA)Sn2I7 (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium, and FA = formamidinium), are reported. Structural characterization reveals that (4AMP)SnI4 is polar with in-plane spontaneous polarization whereas (4AMP)(MA)Sn2I7 and (4AMP)(FA)Sn2I7 are centrosymmetric. Further, (4AMP)SnI4 displays second harmonic generation (SHG) and polarization-electric field hysteresis measurements confirm it is ferroelectric with a spontaneous polarization of 10.0 µC cm-2 at room temperature. (4AMP)SnI4 transitions into a centrosymmetric structure above 367 K. As the first direct experimental observation of the spontaneous ferroelectric polarization of a Sn-based 2D hybrid perovskite, this work opens up environmentally friendly 2D tin halide perovskites for ferroelectricity and other physical property studies.

Chemical Vapor Deposition Synthesis of Intrinsic High-Temperature Ferroelectric 2D CuCrSe2.

Ultrathin 2D ferroelectrics with high Curie temperature are critical for multifunctional ferroelectric devices. However, the ferroelectric spontaneous polarization is consistently broken by the strong thermal fluctuations at high temperature, resulting in the rare discovery of high-temperature ferroelectricity in 2D materials. Here, a chemical vapor deposition method is reported to synthesize 2D CuCrSe2 nanosheets. The crystal structure is confirmed by scanning transmission electron microscopy characterization. The measured ferroelectric phase transition temperature of ultrathin CuCrSe2 is about ≈800 K. Significantly, the switchable ferroelectric polarization is observed in ≈5.2nm nanosheet. Moreover, the in-plane and out-of-plane ferroelectric response are modulated by different maximum bias voltage. This work provides a new insight into the construction of 2D ferroelectrics with high Curie temperature.

The H/F substitution strategy can achieve large spontaneous polarization in 1D hybrid perovskite ferroelectrics.

Hybrid organic-inorganic perovskite (HOIP) ferroelectrics exhibit polarization reversibility and have a wide range of applications in the fields of smart switches, memorizers, sensors, etc. However, the inherent limitations of small spontaneous polarization (P s) and large coercive field (E c) in ferroelectrics have impeded their broader utilization in electronics and data storage. Molecular ferroelectrics, as a powerful supplement to inorganic ferroelectrics, have shown great potential in the new generation of flexible wearable electronic devices. The important research responsibility is to greatly improve progressiveness and overcome the above limitations. Here, a novel one-dimensional (1D) HOIP ferroelectric, (3-F-BTAB)PbBr3 (3-F-BTAB = 3-fluorobenzyltrimethylammonium), was successfully synthesized by employing the H/F substitution strategy to modify parent compound (BTAB)PbBr3 (BTAB = benzyltrimethylammonium), which undergoes a ferroelectric phase transition with Aizu notation 2/mF2 at 420 K. Notably, (3-F-BTAB)PbBr3 demonstrates exceptional ferroelectric properties with a large P s of 7.18 μC cm-2 and a low E c of 1.78 kV cm-1. As far as we know, (3-F-BTAB)PbBr3 features the largest P s among those reported for 1D lead-based HOIP ferroelectrics. This work enriches the 1D lead-based ferroelectric family and provides guidance for applying ferroelectrics in low-voltage polar memories.

Ferroelectric spontaneous polarization assisted TiO2@BaTiO3@Ag photoanode for efficient photoelectrochemical water splitting via BaTiO3 phase regulation

In this work, TiO2@BaTiO3@Ag composite photoanodes were synthesized. By fabricating BaTiO3 with different phase structures, the influence of crystalline phase of BaTiO3 on PEC water splitting was investigated. Furthermore, hot electrons generated in the plasmonic effect of Ag nanoparticles can be efficiently injected into TiO2 film with the assistance of spontaneous polarization electric field (SPEF). Benefitting from this SPEF coupled plasmonic effect, the optimized TiO2@BaTiO3@Ag photoanode (T-TB@Ag) achieved a maximum photocurrent density of 7.30 mA cm−2 (1.23 V vs. RHE) under AM 1.5 G simulated sunlight, which is 6 times that of the non-ferroelectric cubic phase TiO2@BaTiO3@Ag photoanode (C-TB@Ag). This ferroelectric spontaneous polarization coupling plasmonic effect can effectively reduce carrier recombination and promote the separation of photocarriers, which ultimately increases PEC water splitting activity.

Van der Waals Ferroelectrics: Theories, Materials, and Device Applications.

In recent years, an increasing number of 2D van der Waals (vdW) materials are theory-predicted or laboratory-validated to possess in-plane (IP) and/or out-of-plane (OOP) spontaneous ferroelectric polarization. Due to their dangling-bond-free surfaces, interlayer charge coupling, robust polarization, tunable energy band structures, and compatibility with silicon-based technologies, vdW ferroelectric materials exhibit great promise in ferroelectric memories, neuromorphic computing, nanogenerators, photovoltaic devices, spintronic devices, and so on. Here, the very recent advances in the field of vdW ferroelectrics (FEs) are reviewed. First, theories of ferroelectricity are briefly discussed. Then, a comprehensive summary of the non-stacking vdW ferroelectric materials is provided based on their crystal structures and the emerging sliding ferroelectrics. In addition, their potential applications in various branches/frontier fields are enumerated, with a focus on artificial intelligence. Finally, the challenges and development prospects of vdW ferroelectrics are discussed.

Ferromagnetism and ferroelectricity in a superlattice of antiferromagnetic perovskite oxides without ferroelectric polarization

We study the structural, electronic, and magnetic properties of the SrCrO3/YCrO3 superlattice and their dependence on epitaxial strain. We discover that the superlattice adopts A-type antiferromagnetic (A-AFM) ordering in contrast to its constituents (SrCrO3: C-AFM; YCrO3: G-AFM) and retains it under compressive strain while becoming ferromagnetic (5 μB per formula unit) at +1% strain. The obtained ferroelectric polarization is significantly higher than that of the R2NiMnO6/La2NiMnO6 (R = Ce to Er) series of superlattices [Nat. Commun. 5, 4021 (2014)] due to a large difference between the antipolar displacements of the Sr and Y cations. The superlattice is a hybrid-improper multiferroic material with a spontaneous ferroelectric polarization (13.5 μC/cm2) approaching that of bulk BaTiO3 (19 μC/cm2). The combination of ferromagnetism with ferroelectricity enables multistate memory applications. In addition, the charge-order-driven p-type semiconducting state of the ferromagnetic phase (despite the metallic nature of SrCrO3) is a rare property and interesting for spintronics. Monte Carlo simulations demonstrate a magnetic critical temperature of 90 K for the A-AFM phase without strain and of 115 K for the ferromagnetic phase at +5% strain, for example.

A New Relaxor Ferroelectrics Ba4SrBiTi3Nb7O30 with Tungsten Bronze Structure

This paper reports the synthesis, microstructure and electrical properties of a new Ba4SrBiTi3Nb7O30 ceramic. X-ray diffraction analysis shows that the sample crystallizes into tungsten bronze structure, and the space group is P4bm. The electrical measurement results show that Ba4SrBiTi3Nb7O30 exhibits good dielectric and ferroelectric properties. The temperature-dependent dielectric permittivity indicates that the transition temperature of the prepared Ba4SrBiTi3Nb7O30 sample is around Tm ≈ 250K. With increasing the frequency, the dielectric peak moves to a lower temperature. Below 250 K, obvious polarization current can be detected, corresponding to the formation of spontaneous ferroelectric polarization. These results indicate the relaxor ferroelectric behavior of Ba4SrBiTi3Nb7O30 ceramic.

Defect Dipole Behaviors on the Strain Performances of Bismuth Sodium Titanate-Based Lead-Free Piezoceramics.

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight.

Utilizing Cationic Vacancies and Spontaneous Polarization on Cathode to Enhance Zinc‐Ion Storage and Inhibit Dendrite Growth in Zinc‐Ion Batteries

AbstractHigh energy density and intrinsic safety are the central pursuits in developing rechargeable Zinc‐ion batteries (ZIBs). The capacity and stability of nickel cobalt oxide (NCO) cathode are unsatisfactory because of its semiconductor character. Herein, we propose a built‐in electric field (BEF) approach by synergizing cationic vacancies and ferroelectric spontaneous polarization on cathode side to facilitate electron adsorption and suppress zinc dendrite growth on the anode side. Concretely, NCO with cationic vacancies was constructed to expand lattice spacing for enhanced zinc‐ion storage. Heterojunction with BEF leads to the Heterojunction//Zn cell exhibiting a capacity of 170.3 mAh g−1 at 400 mA g−1 and delivering a competitive capacity retention of 83.3 % over 3000 cycles at 2 A g−1. We conclude the role of spontaneous polarization in suppressing zinc dendrite growth dynamics, which is conducive to developing high‐capacity and high‐safety batteries via tailoring defective materials with ferroelectric polarization on the cathode.

Utilizing Cationic Vacancies and Spontaneous Polarization on Cathode to Enhance Zinc-Ion Storage and Inhibit Dendrite Growth in Zinc-Ion Batteries.

High energy density and intrinsic safety are the central pursuits in developing rechargeable Zinc-ion batteries (ZIBs). The capacity and stability of nickel cobalt oxide (NCO) cathode are unsatisfactory because of its semiconductor character. Herein, we propose a built-in electric field (BEF) approach by synergizing cationic vacancies and ferroelectric spontaneous polarization on cathode side to facilitate electron adsorption and suppress zinc dendrite growth on the anode side. Concretely, NCO with cationic vacancies was constructed to expand lattice spacing for enhanced zinc-ion storage. Heterojunction with BEF leads to the Heterojunction//Zn cell exhibiting a capacity of 170.3 mAh g-1 at 400 mA g-1 and delivering a competitive capacity retention of 83.3% over 3000 cycles at 2 A g-1. We conclude the role of spontaneous polarization in suppressing zinc dendrite growth dynamics, which is conducive to developing high-capacity and high-safety batteries via tailoring defective materials with ferroelectric polarization on the cathode.

Strain‐Induced Ferroelectric Phase Transition in Group‐V Monolayer Black Phosphorus

AbstractRecently, a variety of elemental ferroelectric materials have been predicted in group‐V monolayers. However, black phosphorus, as a well‐known group‐V system with the similar structure, seems to be absent of spontaneous ferroelectric polarization. Based on first‐principles calculations, ferroelectric phase in monolayer black phosphorus (BP) is successfully obtained by strain engineering and the driving force can be attributed to Jahn–Teller effect. In addition, the bandgap of the monolayer BP is found to be tunable with applied strain, which can be adjusted to even achieve the metal polarization states. The work not only provides a new route to explore elemental ferroelectricity in 2D materials, but also suggests strain engineering as a powerful tool in related research.

Spontaneous polarization-driven charge migration in BaTiO3/Co3O4/C for enhanced catalytic performance

Ferroelectric spontaneous polarization is a common physical phenomenon that stems from the displacement of positive and negative charges in opposite directions within ferroelectric materials.

Optical reading of multistate nonvolatile oxide memories based on the switchable ferroelectric photovoltaic effect

Intensive research into functional oxides has been triggered by the quest for a solid-state universal memory with high-storage density, non-volatility, high read/write speed, and random access. The ferroelectric random-access memory (FeRAM), in which the information is stored in the spontaneous ferroelectric polarization of the material, offers great promise as nonvolatile and multistate memory, but its destructive electrical reading step requires a rewrite step after each reading, increasing energy consumption. As an alternative, optical nondestructive readout is based on the ferroelectric polarization dependence of the photovoltaic response in materials and has been reported in two-states ferroelectric memories and multistate devices with limited photocurrent switchability due to asymmetric interfacial effects. In this work, we report a nonvolatile oxide memory device based on a symmetric heterostructure with eight stable and well-controlled remanent polarization (Pr) states, written electrically by voltage pulse and read optically through polarization-dependent short-circuit photocurrent Isc or open circuit photovoltage Voc. This symmetric capacitor demonstrates a clear proportionality between Isc (Voc) and Pr, allowing to achieve a 100% switchability of the photovoltaic response. The memory devices based on 3-bit data storage show good performance in terms of data retention, fatigue behavior, and repeatability of writing and reading cycles. Thanks to the very high sensitivity of the optical reading method, the number of states could largely exceed eight, being limited only by the electrical writing step precision. These results are particularly exciting for the development of next-generation ferroelectric memory devices with increased memory storage density and lower power consumption.

“Polymer-in-ceramic” PEO/2D heterojunction composite electrolytes for solid-state batteries

The ferroelectric spontaneous polarizability of the piezoelectric TBA+CNO− also has an enhanced effect on ion transport and electrode interface modification, and its ferroelectric spontaneous polarization field also helps to reduce the generation and growth of anode dendrites. The structural instability of LRAP electrolyte Li2.99Ba0.005OCl are maintained by forming a heterojunction structure with two-dimensional nanosheets TBA+CNO−, and the fast conduction channels of lithium ions (Li+) are established. Composite electrolytes possess Li+ conductivity σi > 10−4 S/cm at 25°C. The composite materials composed of “polymer-in-ceramic” with flexibility and mechanical strength are fabricated by the casting method. PEO-Li2.99Ba0.005OCl/TBA+CNO− shows good compatibility with lithium metal, forming a stable solid electrolyte interface. The plastic crystal electrolyte dripped on the cathode side avoids the direct contact between high-voltage cathode and electrolyte and protects PEO from being oxidized and decomposed. NCM811|Li batteries show 70.9 mAh•g−1 with capacity retention of 97.88% after 100 cycles.

Multifunctional characteristics of zero-dimensional hybrid organic manganese chloride perovskites

In recent years, metal halide perovskites have been developed to create materials that are nontoxic and highly luminescent. Tin, copper, germanium, zinc, bismuth, and other lead-free perovskites have been produced the potential applications in optoelectronic devices. Here, the zero-dimensional hybrid inorganic-organic perovskite structure of hexaimidazolium tetrachloromanganate(II) hexachloromanganate(II), (C3H5N2)6[MnCl4][MnCl6] or HImMC, with red Mn2+-centered phosphorescence at 660 nm with (t2g)3(eg)2 → (t2g)4(eg)1 electronic transition in octahedral geometry and stability under high temperature (∼450 K), is reported. The optical band gap of HImMC is about 3.8 eV. Moreover, this 0 D hybrid perovskite exhibit large ferroelectric spontaneous polarization of 3.2 μC/cm2 at room temperature. Hence, the newly described member of the 0 D organic-inorganic hybrid perovskite family holds significant promise for optoelectronic devices.

Ferroelectric polarization controlled surface potential and charge transport across ITO-Nd-doped BiFeO3 polycrystalline ceramic bulk for photoelectrochemical solar water splitting

The spontaneous polarization in ferroelectrics provides an effective way to engineer interfacial charge distribution at the ferroelectric heterojunctions, thereby depletion width in p-n junction and energy band structures. Here, we integrated p-type multiferroic 7% neodymium-doped bismuth ferrite Bi0.93Nd0.07FeO3 (BFO7Nd) polycrystalline ceramic bulk with n-type transparent conductive indium tin oxide (ITO) to demonstrate the influence of ferroelectric polarization on surface potential and its effect on photoelectrochemical (PEC) water reduction. Kelvin probe force microscopy (KPFM) results reveal the surface potential change during ferroelectric polarization switching, suggesting that the polarization bound charges may have an effect on space charge region between ITO-BFO7Nd, thus dominating surface potential at the electrode/electrolyte interface. This implies that the interface barrier between ITO and BFO7Nd can be easily modulated by polarization bound charges. The electron lifetime of upward-polarization (P-up) ITO-BFO7Nd is estimated 29.30 ms, about 15 times longer than unpoled ITO-BFO7Nd. The photocurrent density of P-up ITO-BFO7Nd is ∼1.2 × 10−6 A/cm2 (at 0 V vs RHE), which is one-order higher compared to that of the unpoled and P-down states under illumination with an intensity of 100 mWcm−2. This work shows that ferroelectric polarization combined with photogenerated carriers is an effective approach for effective charge transfer in multiferroic ceramic to boost PEC solar water splitting.

Pulsed Lased Deposition of Single-Crystalline (001) Oriented Pb(Zr0.5T0.5)O3 Thin Film on PrScO3 Substrate

High quality thin films are important for domain engineering applications such as on-volatile memory applications. Single crystalline (001) oriented Pb (Zr0.5T0.5)O3 thin films have been grown by pulsed laser deposition on PrScO3 with strontium ruthenate (SRO) electrodes. Thin films were prepared from PZT ceramic targets with 15% excess PbO to compensate for lead loss at high deposition temperature. Layer by layer/step flow growth mode observed on AFM images has been realised by using a single terminated PrScO3 substrate as well as optimized deposition parameters. XRD measurements have confirmed the highly (001) oriented tetragonal symmetry. Furthermore, analysis conducted using piezoresponse force microscopy has shown that the thin films are monodomain with spontaneous ferroelectric polarization preferentially pointing upwards, i.e., away from the substrate. The absence of ferroelastic domains and the observed single ferroelectric domain structure are the results of both relatively small compressive misfit strain as well as favourable electrical boundary conditions.
 Keywords: PZT; Pulsed Laser Deposition; Epitax; Thin film