Coexistence Of Ferroelectricity Research Articles

Intrinsic multiferroicity in molybdenum oxytrihalides nanowires

Low-dimensional multiferroics, which simultaneously possess at least two primary ferroic order parameters, hold great promise for post-Moore electronic devices. However, intrinsic one-dimensional (1D) multiferroics with the coexistence of ferroelectricity and ferromagnetism are still yet to be realized, which will be not only crucial for exploring the interplay between low-dimensionality and ferroelectric/ferromagnetic ordering but also significant in rendering application approaches for high density information technologies. Here, we present a theoretical prediction of intrinsic multiferroicity in 1D molybdenum oxytrihalides nanowires, especially focusing on MoOBr3 nanowires which could be readily extracted from experimentally synthesized van der Waals MoOBr3 bulk materials. Due to the spatial inversion symmetry spontaneously broken by Mo atoms’ displacements, MoOBr3 nanowires exhibit 1D ferroelectricity with small coercive electric field and exceptional Curie temperature (~570 K). Additionally, MoOBr3 nanowires also possess 1D antiferroelectric metastable states. On the other hand, both ferroelectric and antiferroelectric MoOBr3 nanowires exhibit ferromagnetic ordering on account of the half-filled Mo-dyz orbitals, a moderate tensile strain (~5%) can greatly boost the spontaneous polarization (~40%) and a mild compress strain (~−2%) may readily switch the magnetic easy axis of ferroelectric MoOBr3 nanowires. Our work holds potential candidates for developing innovative devices that exploit intrinsic multiferroic properties, enabling advancements in novel electronic and spintronic applications.

A Multiferroic Spin-Crossover Molecular Crystal.

Spin-crossover (SCO) ferroelectrics with dual-function switches have attracted great attention for significant magnetoelectric application prospects. However, the multiferroic crystals with SCO features have rarely been reported. Herein, a molecular multiferroic Fe(II) crystalline complex [FeII(C8-F-pbh)2] (1-F, C8-F-pbh = (1Z,N'E)-3-F-4-(octyloxy)-N'-(pyridin-2-ylmethylene)-benzo-hydrazonate) showing the coexistence of ferroelectricity, ferroelasticity, and SCO behavior is presented for the first time. By H/F substitution, the low phase transition temperature (270K) of the non-fluorinated parent compound is significantly increased to 318K in 1-F, which exhibits a spatial symmetry breaking 222F2 type ferroelectric phase transition with clear room-temperature ferroelectricity. Besides, 1-F also displays a spin transition between high- and low-spin states, accompanied by the d-orbital breaking within the t2g 4eg 2 and t2g 6eg° configuration change of octahedrally coordinated FeII center. Moreover, the 222F2 type ferroelectric phase transition is also a ferroelastic one, verified by the ferroelectric domains reversal and the evolution of ferroelastic domains. To the knowledge, 1-F is the first multiferroic SCO molecular crystal. This unprecedented finding sheds light on the exploration of molecular multistability materials for future smart devices.

Novel 2DEG System at the HfO2/STO Interface.

Multifunctional integration in a single device has always been a hot research topic, especially for contradictory phenomena, one of which is the coexistence of ferroelectricity and metallicity. The complex oxide heterostructures, as symmetric breaking systems, provide a great possibility to incorporate different properties. Moreover, finding a series of oxide heterostructures to achieve this goal remains as a challenge. Here, taking the advantage of different physical phenomena, we use H2 plasma to pretreat the SrTiO3 (STO) substrate and then fabricate HfO2/STO heterostructures with it. The novel, well-repeatable metallic two-dimensional electron gas (2DEG) is directly obtained at the heterointerfaces without any further complex procedures, while the obvious ferroelectric-like behavior and Rashba spin-orbit coupling are also observed. The understanding of the mechanism, as well as the modified facile preparation procedure, would be meaningful for further development of ferroelectric metal in complex oxide heterostructures.

Engineering ferroelectric-nanonet-based heterostructures enables superior photovoltaic effect and asymmetric switchability

Layered pervoskite ferroelectrics with a coexistence of robust spontaneous polarization and large intrinsic conductivity exhibit unique photoelectric behavior, and manipulation of photovoltaic response in such ferroelectric-based heterostructure has driven significant research activity. Herein, a Bi2WO6 layered oxide with a coexistence of ferroelectricity and 2D potential well which effectively confines carrier transport was chosen and its orientated nanonet film was formed epitaxially by pulsed laser deposition technique. An excellent platform to investigate the role of the ferroelectric-semiconductor heterostructure in tuning photovoltaic characteristics was constructed by embedding a p-type nanoscale Sb2Se3 within the n-type Bi2WO6 nanonet matrix. The desired Bi2WO6/Sb2Se3 heterostructure optimized the three key steps from light to electricity, and exhibited a large and stable photovoltaic effect, achieving three/two orders of magnitude enhancement of the short-circuit photocurrent density/open-circuit voltage under laser irradiation in its vertical structure device. What is more, an electric-field-controlled switchable asymmetric photoresponse was clearly observed in Bi2WO6/Sb2Se3 device, due to interfacial Schottky barrier formation and its width and height modulation by poling-modified ferroelectric self-polarization. In contrast to classical ferroelectric photovoltaics, the photocurrent direction of the target device after reversed poling remained unchanged, implying the significant role of the polarization-dependent interfacial effect, rather than bulk photovoltaic effect.

Engineering Ferroelectric‐/Ion‐Modulated Conductance in 2D vdW CuInP2S6 for Non‐Volatile Digital Memory and Artificial Synapse

AbstractTwo‐dimensional (2D) ferroionics is appealing in performing complex artificial intelligence tasks due to the interesting property of coexistence of ferroelectricity and ionic activities. CuInP2S6 (CIPS), as a typical 2D ferroionic material, is highly conducive to rich functions of information devices due to the displacement of Cu+ inducing both ferroelectricity and ionic conductivity. However, the coupling and modulation of polarization and ion migration in CIPS for multifunctional information devices has not been fully explored. Here, this study demonstrates that digital memory and synaptic simulations are realized in Au/CIPS/Au device via engineering ferroelectric polarization reversal and the long‐distance migration of the Cu+ to change conductive modes. Steep resistive switching behavior based on ion‐migration is observed with a high on/off ratio of over 108, long retention time (>2 × 104 s), and current compliance engineered multilevel resistance states, demonstrating reliable nonvolatile high‐density memory characteristics. Based on the continuous modulation of polar order, the key synaptic behaviors are successfully simulated. Moreover, by the co‐modulation of polarization state and ions migration, the paired‐pulse facilitation, paired‐pulse depression, and potentiation following depression are achieved. These results suggest that CIPS is a promising candidate for constructing high‐performance, function‐enriched devices for data storage, information processing, and neuromorphic computing.

Coexistence of Ferroelectricity and Ferromagnetism in Atomically Thin Two-Dimensional Cr2S3/WS2 Vertical Heterostructures.

Two-dimensional (2D) heterostructures with ferromagnetism and ferroelectricity provide a promising avenue to miniaturize the device size, increase computational power, and reduce energy consumption. However, the direct synthesis of such eye-catching heterostructures has yet to be realized up to now. Here, we design a two-step chemical vapor deposition strategy to growth of Cr2S3/WS2 vertical heterostructures with atomically sharp and clean interfaces on sapphire. The interlayer charge transfer and periodic moiré superlattice result in the emergence of room-temperature ferroelectricity in atomically thin Cr2S3/WS2 vertical heterostructures. In parallel, long-range ferromagnetic order is discovered in 2D Cr2S3 via the magneto-optical Kerr effect technique with the Curie temperature approaching 170 K. The charge distribution variation induced by the moiré superlattice changes the ferromagnetic coupling strength and enhances the Curie temperature. The coexistence of ferroelectricity and ferromagnetism in 2D Cr2S3/WS2 vertical heterostructures provides a cornerstone for the further design of logic-in-memory devices to build new computing architectures.

Nonzero spontaneous electric polarization in metals: novel predictive methods and applications

Ferroelectricity in metals has advanced since the initial discovery of nonmagnetic ferroelectric-like metal LiOsO_3, anchored in the Anderson and Blount prediction. However, evaluating the spontaneous electric polarization (SEP) of this metal has been hindered by experimental and theoretical obstacles. The experimental challenge arises from difficulties in switching polarization using an external electric field, while the theoretical limitation lies in existing methods applicable only to nonmetals. Zabalo and Stengel (Phys Rev Lett 126:127601, 2021, https://doi.org/10.1103/PhysRevLett.126.127601) addressed the experimental obstacle by proposing flexoelectricity as an alternative for practical polarization switching in LiOsO_3, which requires a critical bending radius similar to BaTiO_3. In this study, we focus on resolving the theoretical obstacle by modifying the Berry phase and Wannier functions approaches within density functional theory plus modern theory of polarization. By employing these modifications, we calculate the SEP of LiOsO_3, comparable to the polarization of BaTiO_3. We validate our predictions using various ways. This study confirms the coexistence of ferroelectricity and metallicity in this new class of ferroelectric-like metals. Moreover, by addressing the theoretical limitation and providing new insights into polarization properties, our study complements the experimental flexoelectricity proposal and opens avenues for further exploration and manipulation of polarization characteristics. The developed approaches, incorporating modified Berry phase and Wannier function techniques, offer promising opportunities for studying and designing novel materials, including bio- and nano-ferroelectric-like metals. This study contributes to the advancement of ferroelectricity in metals and provides a foundation for future research in this exciting field.

Comparison of carrier doping in ZnSnO3 and ZnTiO3 from first principles.

Ferroelectric materials have attracted increasing attention due to their rich properties. Unlike perovskite ferroelectric oxides, in the LiNbO3-type ferroelectric oxides of ABO3, ferroelectrically active cations are not necessary. While the effects of carrier doping on perovskite ferroelectric oxides have been extensively studied, the studies on LiNbO3-type ferroelectric oxides are rare. We consider two LiNbO3-type ferroelectric oxides ZnSnO3 and ZnTiO3, where the former has no ferroelectrically active cation and the latter has ferroelectrically active cation Ti4+, and study the effect of carrier doping by performing first-principles calculations. Comparison results indicate that the B-site cation has significant effects on the polar distortion in LN-type ferroelectrics. Our studies show that LN-type materials can maintain the coexistence of ferroelectricity and conductance over a very wide range of concentrations. The polar displacement is even enhanced under hole doping. More importantly, ZnSnO3 can be doped by electrons up to a high level to realize the conducting ferroelectrics of high mobility due to its isolated s conduction band.

Direct observation of intrinsic room-temperature ferroelectricity in 2D layered CuCrP2S6

Multiferroic materials have ignited enormous interest owing to their co-existence of ferroelectricity and ferromagnetism, which hold substantial promise for advanced device applications. However, the size effect, dangling bonds, and interface effect in traditional multiferroics severely hinder their potential in nanoscale device applications. Recent theoretical and experimental studies have evidenced the possibility of realizing two-dimensional (2D) multiferroicity in van der Waals (vdW) layered CuCrP2S6. However, the incorporation of magnetic Cr ions in the ferroelectric framework leads to antiferroelectric and antiferromagnetic orderings, while macroscopic spontaneous polarization is always absent. Herein, we report the direct observation of robust out-of-plane ferroelectricity in 2D vdW CuCrP2S6 at room temperature with a comprehensive investigation. Modification of the ferroelectric polarization states in 2D CuCrP2S6 nanoflakes is experimentally demonstrated. Moreover, external electric field-induced polarization switching and hysteresis loops are obtained in CuCrP2S6 down to ~2.6 nm (4 layers). By using atomically resolved scanning transmission electron microscopy, we unveil the origin of the emerged room-temperature ferroelectricity in 2D CuCrP2S6. Our work can facilitate the development of multifunctional nanodevices and provide important insights into the nature of ferroelectric ordering of this 2D vdW material.

Engineering room temperature multiferroicity and temperature dependent dielectric properties of Cr doped BaTiO3 ceramics

The coexistence of ferroelectricity, ferromagnetism, and piezoelectricity at room temperature in BaTi1-xCrxO3 (0 ≤ x ≤ 0.06) nanostructures is interesting and leads to the multiferroic nature of system. Sol-gel auto-combustion technique has been used for the synthesis of nanostructures. The XRD patterns along with Rietveld refinement analysis, confirm that the samples possess parent tetragonal perovskite structure in the P4mm space group. The oxygen vacancies stoichiometry ratio was estimated through XPS studies. The scanning electron microscopy (SEM) confirms the large grain size in the doped sample. The study of leakage current density reveals an increase in its value with the increase in Cr content due to defects induced in the system. P-E measurements confirm the ferroelectric nature of the samples that diminishes in the doped samples due to the high leakage current. Moreover, the estimated value of energy efficiency (η) was found to be maximum for the undoped sample. The undoped BaTiO3 has a diamagnetic character that is partially altered into weak ferromagnetic under the Cr-doping at the expense of decreasing polarization parameters. The temperature-dependent dielectric constant shows all characteristics of phase transitions in the samples. The doping of Cr enhances the ferroelectric to paraelectric phase transition temperature (Tc). The piezoelectricity remains preserved in the doped samples. Thus, the coexistence of ferroelectricity, ferromagnetism, and piezoelectricity at room temperature finalizes the multiferroic nature of the synthesized samples.

Structural evolution and coexistence of ferroelectricity and antiferromagnetism in Fe, Nb co-doped BaTiO3 ceramics

Multiferroics are materials that exhibit two or more primary ferroic properties within the same phase and have potential applications in sensors, spintronics and memory devices. Here, the dielectric, ferroelectric and magnetic properties of novel multiferroics derived from BaTi1−x(Fe0.5Nb0.5)xO3 (BTFN, 0.01 ≤ x ≤ 0.10) ceramics are investigated. Multiferroism in these ceramics is manifested by the coexistence of ferroelectric long-range ordering and antiferromagnetism. With increasing x-value, there is a structural evolution from a tetragonal perovskite to a mixture of tetragonal and cubic phases, accompanied by a decrease in the temperature of maximum permittivity. At room temperature, ferroelectric behaviour is evidenced by the presence of current peaks corresponding to domain switching in the current-electric field loops, while the observation of non-linear narrow magnetic hysteresis loops suggests dilute magnetism. The results indicate that in the x = 0.07 composition the antiferromagnetic order is established through an indirect super-exchange interaction between adjacent Fe ions.

Coexistence of Ferroelectricity and Ferromagnetism in Fullerene-Based One-Dimensional Chains.

One-dimensional (1D) magnetoelectric multiferroics are promising multifunctional materials for miniaturized sensors, actuators, and memories. However, 1D materials with both ferroelectricity and ferromagnetismare quite rare. Herein, using first-principles calculations, a series of fullerene-based 1D chains, namely U2 C@C80 -M (M=Cr, Mn, Mo, and Ru) 1D chains with both ferroelectric (FE) and ferromagnetic (FM)properties is designed. Compared to individual U2 C@Ih (7)-C80 , the spontaneous polarization (Ps) in 1D chains is enhanced by about two to four times owing to the interaction between U2 C@Ih (7)-C80 fullerene and M (M=Cr, Mn, Mo, and Ru) atoms. Meanwhile, the introduction of transition metal atoms dopes electrons into U's 5f orbitals, leading to numerous intriguing magnetic properties, such as U2 C@C80 -Cr and U2 C@C80 -Mo as 1D ferromagneticsemiconductors, U2 C@C80 -Ru as 1D ferrimagnetic (FiM) semiconductor, and U2 C@C80 -Mn as 1D antiferromagnetic (AFM) semiconductor. Excitingly, it is found that magnetic ordering and electrical polarization can be modulated independently by linking different transition metal atoms. These findings not only broaden the range of 1D multiferroic materials, but also provide promising candidates for novel electronic and spintronic applications.

Bismuth ferrite-barium titanate system studies around morphotropic phase boundary

Nowadays, the electro-electronic industry and scientific community have a great interest in improving memory devices. A candidate is the bismuth ferrite owing to the coexistence of ferroelectricity and anti-ferromagnetism at room temperature, however, a high leakage current harms their ferroelectric properties. Thus, bismuth ferrite and barium titanate solutions improve the ferroelectric properties of bismuth ferrite and optimize the magnetoelectric coupling factor. This system is called multiferroic, materials exhibit the coexistence of ferromagnetic, ferroelectric, or ferro-elastic orders, which is of interest to the scientific physics community and electronic industry. In this paper, bismuth ferrite-barium titanate system around the morphotropic phase boundary was studied and analyzed. It was observed changes in the structural properties in function of barium titanate content. Calcination temperature was determined from thermogravimetric analysis curves to powders of bismuth ferrite-barium titanate system. Ceramic bodies were densified conventionally. Archimedes’ method was used for density measure. Ceramics with densities greater than 95% were obtained. 93% of the perovskite phase was obtained from structural results. Finally, structural properties were presented and analyzed using Mossbauer spectroscopy as complementary technique. These analyses are very important in solid state physics because to contribute to understanding the phenomenology and synthesis process of multiferroic materials.

Intrinsic ferroelectrics and carrier doping-induced metallic multiferroics in an atomic wire

Low-dimensional multiferroic metals characterized by the simultaneous coexistence of ferroelectricity, conductivity, and magnetism hold tremendous potential for scientific and technological endeavors. However, the mutually exclusive mechanisms among these properties impede the discovery of multifunctional conducting multiferroics, especially at the atomic-scale. Here, based on first-principles calculations, we design and demonstrate intrinsic one-dimensional (1D) ferroelectrics and carrier doping-induced metallic multiferroics in an atomic WOF4 wire. The WOF4 atomic wire that can be derived from a 1D van der Waals crystal exhibits pronounced ferroelectricity manifested in the form of large cooperative atomic displacements. By performing Monte Carlo simulations with an effective Hamiltonian method, we obtain the nanowire that can sustain a high Curie temperature, indicating its potential for room-temperature applications. Moreover, doping with electrons is found to induce magnetism and metallic conductivity that coexists with the ferroelectric distortion in the nanowire. These appealing properties in conjunction with the experimental feasibility enable the doped WOF4 nanowire to act as a promising atomic-scale multifunctional material.

Coexistence of ferroelectricity and ferromagnetism in hex-GeS nanowires.

The existence of one-dimensional (1D) ferroelectricity and ferromagnetism provides an opportunity to expand the field of research in low-dimensional magnetoelectric and multiferroics and explore the future development of high-performance nanometer devices. Here, we predict a novel 1D ferroelectric hex-GeS nanowire with coexisting ferromagnetism. The electric polarization comes from the atomic displacements between Ge and S atoms, and it exhibits a far-higher than room temperature ferroelectric Curie temperature TEc = 830 K. The ferromagnetism, stemming from the Stoner instability, can be tuned by hole doping and maintained over a wide range of hole concentrations. Additionally, an indirect-direct-indirect band gap transition can be achieved via strain engineering and the bonding nature of the near-band-edge electronic orbitals revealed this transition mechanism. These results offer a platform to investigate 1D ferroelectric and ferromagnetic systems, and the presented hex-GeS nanowire demonstrates the potential for high-performance electronic and spintronic applications.

One dimensional ferroelectric nanothreads with axial and radial polarization.

Long-range ferroelectric crystalline order usually fades away as the spatial dimension decreases, and hence there are few two-dimensional (2D) ferroelectrics and far fewer one-dimensional (1D) ferroelectrics. Due to the depolarization field, low-dimensional ferroelectrics rarely possess the polarization along the direction of reduced dimensionality. Here, using first-principles density functional theory, we explore the structural evolution of nanoribbons of varying widths constructed by cutting a 2D sheet of ferroelectric α-III2VI3 (III = Al, Ga, In; VI = S, Se, Te). We discover a one-dimensional ferroelectric nanothread (1DFENT) of ultrasmall diameter with both axial and radial polarization, potentially enabling ultra-dense data storage with a 1D domain of just three unit cells being the functional unit. The polarization in 1DFENT of Ga2Se3 exhibits an unusual piezoelectric response: a stretching stress along the axial direction will increase both the axial and radial polarization, referred to as the auxetic piezoelectric effect. Utilizing the intrinsically flat electronic bands, we demonstrate the coexistence of ferroelectricity and ferromagnetism in 1DFENT and a counterintuitive charge-doping-induced metal-to-insulator transition. The 1DFENT with both axial and radial polarization offers a counterexample to the Mermin-Wagner theorem in 1D and suggests a new platform for the design of ultrahigh-density memory and the exploration of exotic states of matter.

Axial-Chiral BINOL Multiferroic Crystals with Coexistence of Ferroelectricity and Ferroelasticity.

Chirality exists everywhere from natural amino acids to particle physics. The introduction of point chirality has recently been shown to be an efficient strategy for the construction of molecular ferroelectrics. In contrast to point chirality, however, axial chirality is rarely used to design ferroelectrics so far. Here, based on optically active 1,1'-bi-2-naphthol (BINOL), which has been applied extensively as a versatile chiral reagent in asymmetric catalysis, chiral recognition, and optics, we successfully design a pair of axial-chiral BINOL multiferroics, (R)-BINOL-DIPASi and (S)-BINOL-DIPASi. They experience a 2F1-type full ferroelectric/ferroelastic phase transition at a high temperature of 362 and 363 K, respectively. Piezoelectric force microscopy and polarization-voltage hysteresis loops demonstrate their ferroelectric domains and domain switching, and polarized light microscopy visualizes the evolution of stripe-shaped ferroelastic domains. The axial-chiral BINOL building block promotes the generation of the polar structure and ferroelectricity, and the organosilicon component increases the rotational energy barrier and thus the phase transition temperature. This work presents the first axial-chiral high-temperature multiferroic crystals, offering an efficient path for designing molecular multiferroics through the introduction of axial chirality.

The evolution of ferroelectricity and ferromagnetism in epitaxial and freestanding SrTiO3-σ thin films

Tuning single-crystalline transition metal oxide to possess multi functionalities, for instance, ferroelectricity and ferromagnetism through strain and defect engineering is crucial for facilitating related functionalities that have implications for device applications. To clarify the dependence relationship between strain and defect for emergent ferroics in complex oxide, in this study, we report the ferroelectric and magnetic properties of oxygen-deficient SrTiO3-σ (STO3-σ) thin films in rigid heterostructure and freestanding forms. By an appropriate introduction of oxygen vacancies, the STO3-σ exhibits the coexistence of ferroelectricity and ferromagnetism in its rigid heterostructure, however, these features are eliminated if STO3-σ turns to the freestanding thin films via a water-dissolution of Sr3Al2O6 (SAO) sacrifice interlayer. Our experimental findings demonstrate that both ferroelectricity and ferromagnetism of STO3-σ need the stabilization of the defects by strain which enlarges the activation energy of the anionic defect suggesting a promising multiferroic engineering method. Meanwhile, our study also provides valuable information on flexoelectric/flex magnet devices.

Structure domains induced nonswitchable ferroelectric polarization in polar doubly cation-ordered perovskites

Double perovskites with cation ordering allow the coexistence of ferroelectricity and magnetization in the same phase, and thus become a good candidate for room-temperature multiferroic materials. In this paper, we successfully synthesized A- and B-site ordered double perovskites NaLnBWO6 (Ln = La, Nd, and BMg, Mn) ceramics, and investigated their microstructure by combining X-ray diffraction, aberration-corrected scanning transmission electron microscopy, and optical second harmonic generation measurements. At room temperature, both NaLaMgWO6 and NaNdMgWO6 ceramics possess the space group of P21/m, while NaLaMnWO6 has a polar crystal structure (P21) without inversion symmetry. All three samples exhibit the A-site layered ordering and B-site rock-salt ordering as directly imaged by the HAADF-STEM images. The observed structural domains arising from the cation ordering well explain the nonswitchable ferroelectric polarization due to a large energy barrier. These findings suggest that it is necessary to eliminate structural domains during the sample synthesis for obtaining large ferroelectric polarization in double perovskites.

Homochiral Multiferroic Cyanido‐Bridged Dimetallic Complexes Assembled by C−F⋅⋅⋅K Interactions

AbstractCyanido‐bridged dimetallic complexes are attracting attention due to their varied structures and properties. However, homochiral cyanido‐bridged dimetallic complexes are rare, and making them ferroelectric is a great challenge. Introducing C−F⋅⋅⋅K interactions between the guest chiral cations and the host [KFe(CN)6]2− framework, gives three‐dimensional cyanido‐bridged dimetallic multiferroics, [R‐ and S‐3‐fluoropyrrolidinium]2[KFe(CN)6] (R‐ and S‐3‐FPC). The mirror‐symmetric vibrational circular dichroism (VCD) signal shows their enantiomeric nature. R‐ and S‐3‐FPC crystallize in the same chiral‐polar space group P21 at 298 K. Piezoresponse force microscopy (PFM), polarizing optical microscopy, and temperature‐dependent second‐harmonic generation (SHG) measurements show their multiferroic properties (the coexistence of ferroelectricity and ferroelasticity), in line with the Aizu notation of 222F2. R‐3‐FPC shows excellent ferroelectricity with saturated polarization up to 9.4 μC cm−2.