Interfacial ferroelectricity is a recently established mechanism for generating spontaneous reversible electric polarization,arising from the charge transfer between stacked van der Waals layered atomic crystals.It ha...Interfacial ferroelectricity is a recently established mechanism for generating spontaneous reversible electric polarization,arising from the charge transfer between stacked van der Waals layered atomic crystals.It has been realized in both naturally formed multilayer crystals and moirésuperlattices.Owing to the large number of material choices and combinations,this approach is highly versatile,greatly expanding the scope of ultrathin ferroelectrics.A key advantage of interfacial ferroelectricity is its potential to couple with preexisting properties of the constituent layers,enabling their electrical manipulation through ferroelectric switching and paving the way for advanced device functionalities.This review article summarizes recent experimental progress in interfacial ferroelectricity,with an emphasis on its coupling with a variety of electronic properties.After introducing the underlying mechanism of interfacial ferroelectricity and the range of material systems discovered to date,we highlight selected examples showcasing ferroelectric control of excitonic optical properties,Berry curvature effects,and superconductivity.We also discuss the challenges and opportunities that await further studies in this field.展开更多
Doped HfO_(2)as an emerging ferroelectric material,holds considerable promise for non-volatile memory applications.Epitaxial growth of doped HfO_(2)thin films is widely adopted as an effective technique for revealing ...Doped HfO_(2)as an emerging ferroelectric material,holds considerable promise for non-volatile memory applications.Epitaxial growth of doped HfO_(2)thin films is widely adopted as an effective technique for revealing the intrinsic ferroelectric properties.In this study,based on systematic structural,chemical and electrical investigations,the influences of Mn doping and substrate orientation on ferroelectric properties of Mn-doped HfO_(2)epitaxial thin films are investigated.The results demonstrate that Mn-doped HfO_(2)thin films with orthorhombic phase can be epitaxially grown along[111]out-of-plane direction on both SrTiO_(3)(001)and(110)substrates,and 10%Mn-doping significantly stabilizes the orthorhombic polar phase and enhances the ferroelectric polarization.Interestingly,compared to the films on SrTiO_(3)(001)substrate,the better crystallinity and reduction of oxygen vacancy amount in Mn-doped HfO_(2)films grown on the SrTiO_(3)(110)substrate are observed,which enhance the remanent polarization and reduce the coercive field.It provides an effective approach for the controllable regulation of defects and the enhancement of intrinsic ferroelectricity in HfO_(2)-based materials.展开更多
Poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)) is a derivative of polyvinylidene fluoride(PVDF), known for its excellent ferroelectric properties, optical characteristics, chemical stability, and flexibility...Poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)) is a derivative of polyvinylidene fluoride(PVDF), known for its excellent ferroelectric properties, optical characteristics, chemical stability, and flexibility, making it a promising material for applications in electronic devices. In this study, the polarization switching mechanism of the β-phase of P(VDFTrFE) is investigated using the polarized crystal charge method, along with molecular dynamics simulations. The simulation results show that the saturation polarization value is approximately 5.3 μC/cm^(2), and a coercive field of around 0.5 V/nm is required to switch its polarization states. By fitting the polarization reversal curve with the Kolmogorov–Avrami–Ishibashi model, it is observed that the data in the asymptotic and switching regions closely align with the predictions of the model,and the Avrami index n consistently ranges between 1 and 2. The polarization reversal is completed within approximately10 ps, demonstrating high-speed dynamic behavior. Additionally, we predict that the ferroelectric phase transition occurs between 420 K and 430 K, with stable polarization performance maintained over a wide temperature range, which is consistent with experimental results.展开更多
Ferroelectric materials are widely applied in the ferroelectronic devices,photovoltaics,and so on.Ultrathin ferroelectric thin films are highly desired for their applications,which still remain a challenge.In this wor...Ferroelectric materials are widely applied in the ferroelectronic devices,photovoltaics,and so on.Ultrathin ferroelectric thin films are highly desired for their applications,which still remain a challenge.In this work,the ultrathin barium titanate(BaTiO_(3),BTO)films are deposited directly on the fluorine-doped tin oxide glass(SnO_(2):F,FTO)substrates by radio frequency magnetron sputtering method at different temperatures.All BTO ultrathin films exhibit strong ferroelectric properties.Interestingly,BTO thin films deposited at room temperature(RT)also exhibit robust ferroelectricity.The polar domains are switched reversibly with a phase degree of~180°by piezoelectric force microscopy for the BTO thin films deposited at room temperature,attributing to the strain and ion migration.展开更多
We report the discovery of bistable polar states with switchable polarization in the Janus monolayer 1T-MoSSe,induced by symmetry breaking in its chalcogen atomic layers.Our results demonstrate that Janus 1T-MoSSe exh...We report the discovery of bistable polar states with switchable polarization in the Janus monolayer 1T-MoSSe,induced by symmetry breaking in its chalcogen atomic layers.Our results demonstrate that Janus 1T-MoSSe exhibits two out-of-plane bistable polar states with switchable polarization,rather than polarization emerging from a non-polar phase,which represents an unconventional form of ferroelectric-like behavior.First-principles calculations and phenomenological modeling reveal that the inequivalent stacking of sulfur and selenium(S/Se)atoms breaks central inversion symmetry,activating non-degenerate phonon modes at the K-point(K_(2)/K_(3))that drive the structural transformation between metastable d1TS and d1TSe phases.This coupling enables bipolar control of out-of-plane polarization through atomic displacements and charge redistribution,resulting in a polarization change ofΔP≈±0.3μC/cm^(2).The Landau free energy analysis indicates that anharmonic terms and inter-mode coupling generate an asymmetric double-well potential,which is essential for the stabilization of bistable polar states.Molecular dynamics simulations show that the d1TS phase remains stable at high temperatures,whereas the d1TSe phase undergoes an irreversible phase transition near 300 K,accompanied by a Peierls-like distortion of the Mo atomic chain.This transition is driven by differences in electronegativity,atomic radius,and d-p orbital hybridization between S and Se.Our findings establish a theoretical framework for engineering nonlinear responses in two-dimensional(2D)ferroelectrics and suggest that low-energy polarization reversal at room temperature can be achieved through strain or electric-field control,offering promising opportunities for non-volatile memory and piezoelectric sensing applications.展开更多
Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its...Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.展开更多
Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,...Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,the crystallization of polar orthorhombic phase(o-phase)HfO_(2)is less competitive,which greatly limits the ferroelectricity of the as-obtained ferroelectric HfO_(2)thin films.Fortunately,the crystallization of o-phase HfO_(2)can be thermodynamically modulated via interfacial stress engineering.In this paper,the growth of improved ferroelectric Al doped HfO_(2)(HfO_(2):Al)thin films on(111)-oriented Si substrate has been reported.Structural analysis has suggested that nonpolar monoclinic HfO_(2):Al grown on(111)-oriented Si substrate suffered from a strong compressive strain,which promoted the crystallization of(111)-oriented o-phase HfO_(2)in the as-grown HfO_(2):Al thin films.In addition,the in-plane lattice of(111)-oriented Si substrate matches well with that of(111)-oriented o-phase HfO_(2),which further thermally stabilizes the o-phase HfO_(2).Accordingly,an improved ferroelectricity with a remnant polarization(2P_(r))of 26.7C/cm^(2) has been obtained.The results shown in this work provide a simple way toward the preparation of improved ferroelectric HfO_(2)thin films.展开更多
The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are fre...The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.展开更多
Since the appearance of Rochelle salt,ferroelectrics have received extensive attention from researchers due to they are playing an important role in sensors,memories,mechanical actuation,and so on.In recent years,with...Since the appearance of Rochelle salt,ferroelectrics have received extensive attention from researchers due to they are playing an important role in sensors,memories,mechanical actuation,and so on.In recent years,with the rapid development of molecular ferroelectrics,high-performance molecular ferroelectrics have become effective complement to inorganic ferroelectrics.However,compared with inorganic ferroelectrics,the family of molecular ferroelectrics is relatively scarce,and exploring highperformance ferroelectric materials through new synthesis strategies has become the trend of molecular ferroelectrics.Here,we successfully transformed non-polar material 1(2-H_(2)PCA)_(2)(H_(2)O)CdCl_(6)(2-H_(2)PCA=2-picolylamine cation)into polar material 2(2-H_(2)PCA)2CdCl_(6)by single-crystal to single-crystal transformation(SCSCT).Meanwhile,2 exhibits clear ferroelectricity with a high-temperature Tc of 378 K,a Ps of 1.18μC/cm^(2)at 300 K.This work not only realizes the purpose of synthesizing ferroelectrics by forming polar structures by SCSCT,but also realizes the reversibility of SCSCT,which provides ideas for the construction and exploration of new molecular ferroelectrics.展开更多
The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sa...The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.展开更多
Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more com...Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.展开更多
The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effe...The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effect and ferroelectricity in group-V elemental layers,has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit.In this review,we comprehensively review recent research progress in engineering of topology and ferroelectricity,and several effective methods to control the quantum phase transition are discussed.We then introduce the coupling between topological orders and ferroelectric orders.The research directions and outlooks are discussed at the end of the perspective.It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.展开更多
The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future pr...The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future prospects for the ferroelectric HfO_(2)-based thin films and devices are presented from fundamentals to applications.The related issues are discussed,which include:1)The ferroelectric characteristics observed in HfO_(2)-based films and devices associated with the factors of dopant,strain,interface,thickness,defect,fabrication condition,and more;2)physical understanding on the observed ferroelectric behaviors by the density functional theory(DFT)-based theory calculations;3)the characterizations of microscopic and macroscopic features by transmission electron microscopes-based and electrical properties-based techniques;4)modeling and simulations,5)the performance optimizations,and 6)the applications of some ferroelectric-based devices such as ferroelectric random access memory,ferroelectric-based field effect transistors,and the ferroelectric tunnel junction for the novel information processing systems.展开更多
In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage ...In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.展开更多
5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements f...5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.展开更多
We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarizatio...We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarization.The first one is the orientation of polarized water molecules staying in the R2 region of SnIP.The second one is the displacement of I atom which roots from subtle interaction with absorbed water molecules.A reasonable scenario of polarization flipping is proposed in this study.In the scenario,the water molecule is rolling-up with keeping the magnitude of its electrical dipole and changing its direction,meanwhile,the displacement of I atoms is also reversed.Highly tunable polarization can be achieved by applying strain,with 26.5%of polarization enhancement by applying tensile strain,with only 4%degradation is observed with 4%compressive strain.Finally,the direct band gap is also found to be correlated with strain.展开更多
Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust m...Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically.Magnetic frustration,which can induce ferroelectricity,gives rise to multiferroic behavior.In this paper,we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity.A disordered stacking of manganites is expected to result in frustration at interfaces.We report here that a tri-color multilayer structure comprised of non-ferroelectric La;Ca;MnO;（A）/Pr;Ca;MnO;（B）/Pr;Sr;MnO;（C） layers with the disordered arrangement of ABC-ACBCAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics.The multilayer film exhibits evidence of ferroelectricity at room temperature,thus presenting a candidate for multiferroics.展开更多
Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in c...Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ＋ is substituted with Mn2＋, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.展开更多
Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detect...Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detected through piezoelectric force microscopy （PFM） by writing reversible ferroelectric domains. However, PLT thin film also shows off-standard ferroelectric hysteresis loops highly dependent on frequency, indicating large amount of mobile space charges in the film. Subsequent current-voltage （C-V） studies show that sandwich-like Pt／PLT／Pt structure exhibits notable bipolar resistive switching （BRS） characteristics with high stability （〉 103 switching cycles）. It is found that the C-V curves of both high- and low-resistance states have the feature of space-charge-limited current （SCLC） conduction, indicating important roles of defects in the conduction. X-ray photoelectron spectroscopy measurement further verifies that oxygen vacancies based conductive filament mechanism is likely responsible for the observed RS effect. Our demonstration of stable RS effect in the PLT thin film and its possible coupling with ferroelectricity is promising in device development and applications, such as development of ferroelectric-tunable RS memories.展开更多
The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properti...The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.展开更多
基金Project supported by the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20231529 and BK20233001)the National Key Research and Development Program of China(Grant No.2024YFA1409100)+2 种基金the Fundamental Research Funds for the Central Universities(Grant No.0204-14380233)the National Natural Science Foundation of China(Grant Nos.12474170 and 123B2059)the National Postdoctoral Program for Innovative Talents(Grant No.BX20240160)。
文摘Interfacial ferroelectricity is a recently established mechanism for generating spontaneous reversible electric polarization,arising from the charge transfer between stacked van der Waals layered atomic crystals.It has been realized in both naturally formed multilayer crystals and moirésuperlattices.Owing to the large number of material choices and combinations,this approach is highly versatile,greatly expanding the scope of ultrathin ferroelectrics.A key advantage of interfacial ferroelectricity is its potential to couple with preexisting properties of the constituent layers,enabling their electrical manipulation through ferroelectric switching and paving the way for advanced device functionalities.This review article summarizes recent experimental progress in interfacial ferroelectricity,with an emphasis on its coupling with a variety of electronic properties.After introducing the underlying mechanism of interfacial ferroelectricity and the range of material systems discovered to date,we highlight selected examples showcasing ferroelectric control of excitonic optical properties,Berry curvature effects,and superconductivity.We also discuss the challenges and opportunities that await further studies in this field.
基金supported by the National Natural Science Foundation of China(Grant Nos.52125204,52250281,52422209,92163210,and U21A2066)the Na-tional Key Research and Development Program of China(Grant Nos.2024YFA1208601,2022YFB3807602,and 2022YFB3807604).
文摘Doped HfO_(2)as an emerging ferroelectric material,holds considerable promise for non-volatile memory applications.Epitaxial growth of doped HfO_(2)thin films is widely adopted as an effective technique for revealing the intrinsic ferroelectric properties.In this study,based on systematic structural,chemical and electrical investigations,the influences of Mn doping and substrate orientation on ferroelectric properties of Mn-doped HfO_(2)epitaxial thin films are investigated.The results demonstrate that Mn-doped HfO_(2)thin films with orthorhombic phase can be epitaxially grown along[111]out-of-plane direction on both SrTiO_(3)(001)and(110)substrates,and 10%Mn-doping significantly stabilizes the orthorhombic polar phase and enhances the ferroelectric polarization.Interestingly,compared to the films on SrTiO_(3)(001)substrate,the better crystallinity and reduction of oxygen vacancy amount in Mn-doped HfO_(2)films grown on the SrTiO_(3)(110)substrate are observed,which enhance the remanent polarization and reduce the coercive field.It provides an effective approach for the controllable regulation of defects and the enhancement of intrinsic ferroelectricity in HfO_(2)-based materials.
基金Project supported by the National Key Research and Development Program of China (Grant No. 2021YFA1200700)the National Natural Science Foundation of China (Grant Nos. 11905054, 12275075, and 11704111)the Fundamental Research Funds for the Central Universities of China。
文摘Poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)) is a derivative of polyvinylidene fluoride(PVDF), known for its excellent ferroelectric properties, optical characteristics, chemical stability, and flexibility, making it a promising material for applications in electronic devices. In this study, the polarization switching mechanism of the β-phase of P(VDFTrFE) is investigated using the polarized crystal charge method, along with molecular dynamics simulations. The simulation results show that the saturation polarization value is approximately 5.3 μC/cm^(2), and a coercive field of around 0.5 V/nm is required to switch its polarization states. By fitting the polarization reversal curve with the Kolmogorov–Avrami–Ishibashi model, it is observed that the data in the asymptotic and switching regions closely align with the predictions of the model,and the Avrami index n consistently ranges between 1 and 2. The polarization reversal is completed within approximately10 ps, demonstrating high-speed dynamic behavior. Additionally, we predict that the ferroelectric phase transition occurs between 420 K and 430 K, with stable polarization performance maintained over a wide temperature range, which is consistent with experimental results.
基金financially supported by the National Key Research and Development Program of China(No.2019YFB1503500)
文摘Ferroelectric materials are widely applied in the ferroelectronic devices,photovoltaics,and so on.Ultrathin ferroelectric thin films are highly desired for their applications,which still remain a challenge.In this work,the ultrathin barium titanate(BaTiO_(3),BTO)films are deposited directly on the fluorine-doped tin oxide glass(SnO_(2):F,FTO)substrates by radio frequency magnetron sputtering method at different temperatures.All BTO ultrathin films exhibit strong ferroelectric properties.Interestingly,BTO thin films deposited at room temperature(RT)also exhibit robust ferroelectricity.The polar domains are switched reversibly with a phase degree of~180°by piezoelectric force microscopy for the BTO thin films deposited at room temperature,attributing to the strain and ion migration.
基金support from the National Natural Science Foundation of China(Grant Nos.12334014 and 11727902)the Overseas High-level Talents Program of the Chinese Academy of Sciences.
文摘We report the discovery of bistable polar states with switchable polarization in the Janus monolayer 1T-MoSSe,induced by symmetry breaking in its chalcogen atomic layers.Our results demonstrate that Janus 1T-MoSSe exhibits two out-of-plane bistable polar states with switchable polarization,rather than polarization emerging from a non-polar phase,which represents an unconventional form of ferroelectric-like behavior.First-principles calculations and phenomenological modeling reveal that the inequivalent stacking of sulfur and selenium(S/Se)atoms breaks central inversion symmetry,activating non-degenerate phonon modes at the K-point(K_(2)/K_(3))that drive the structural transformation between metastable d1TS and d1TSe phases.This coupling enables bipolar control of out-of-plane polarization through atomic displacements and charge redistribution,resulting in a polarization change ofΔP≈±0.3μC/cm^(2).The Landau free energy analysis indicates that anharmonic terms and inter-mode coupling generate an asymmetric double-well potential,which is essential for the stabilization of bistable polar states.Molecular dynamics simulations show that the d1TS phase remains stable at high temperatures,whereas the d1TSe phase undergoes an irreversible phase transition near 300 K,accompanied by a Peierls-like distortion of the Mo atomic chain.This transition is driven by differences in electronegativity,atomic radius,and d-p orbital hybridization between S and Se.Our findings establish a theoretical framework for engineering nonlinear responses in two-dimensional(2D)ferroelectrics and suggest that low-energy polarization reversal at room temperature can be achieved through strain or electric-field control,offering promising opportunities for non-volatile memory and piezoelectric sensing applications.
基金supported by the National Natural Science Foundation of China(Nos.12372331,12072307,and 12302429)the Science and Technology Innovation Program of Hunan Province,China(No.2024RC3160)the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110116).
文摘Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.
基金Research Fund of Guangdong-Hong Kong-Macao Joint Laboratory for Intelligent Micro-Nano Optoelectronic Tech-nology,China(Grant No.2020B1212030010)Project of Faculty of Agricultural Equipment of Jiangsu University (Grant No. NZXB20210202) are acknowledged。
文摘Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,the crystallization of polar orthorhombic phase(o-phase)HfO_(2)is less competitive,which greatly limits the ferroelectricity of the as-obtained ferroelectric HfO_(2)thin films.Fortunately,the crystallization of o-phase HfO_(2)can be thermodynamically modulated via interfacial stress engineering.In this paper,the growth of improved ferroelectric Al doped HfO_(2)(HfO_(2):Al)thin films on(111)-oriented Si substrate has been reported.Structural analysis has suggested that nonpolar monoclinic HfO_(2):Al grown on(111)-oriented Si substrate suffered from a strong compressive strain,which promoted the crystallization of(111)-oriented o-phase HfO_(2)in the as-grown HfO_(2):Al thin films.In addition,the in-plane lattice of(111)-oriented Si substrate matches well with that of(111)-oriented o-phase HfO_(2),which further thermally stabilizes the o-phase HfO_(2).Accordingly,an improved ferroelectricity with a remnant polarization(2P_(r))of 26.7C/cm^(2) has been obtained.The results shown in this work provide a simple way toward the preparation of improved ferroelectric HfO_(2)thin films.
基金supported by the National Key R&D Program of China under Grant No.2022YFB3608400National Natural Science Foundation of China under Grant Nos.61825404,61888102,and 62104044the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No.XDB44000000 and the project of MOE innovation platform.
文摘The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.
基金supported by the National Natural Science Foundation of China(Nos.22175079,22205087 and 22275075)Natural Science Foundation of Jiangxi Province(Nos.20225BCJ23006 and 20224ACB204002)Science and Technology Project of Jiangxi Provincial Department of Education(No.GJJ210880)。
文摘Since the appearance of Rochelle salt,ferroelectrics have received extensive attention from researchers due to they are playing an important role in sensors,memories,mechanical actuation,and so on.In recent years,with the rapid development of molecular ferroelectrics,high-performance molecular ferroelectrics have become effective complement to inorganic ferroelectrics.However,compared with inorganic ferroelectrics,the family of molecular ferroelectrics is relatively scarce,and exploring highperformance ferroelectric materials through new synthesis strategies has become the trend of molecular ferroelectrics.Here,we successfully transformed non-polar material 1(2-H_(2)PCA)_(2)(H_(2)O)CdCl_(6)(2-H_(2)PCA=2-picolylamine cation)into polar material 2(2-H_(2)PCA)2CdCl_(6)by single-crystal to single-crystal transformation(SCSCT).Meanwhile,2 exhibits clear ferroelectricity with a high-temperature Tc of 378 K,a Ps of 1.18μC/cm^(2)at 300 K.This work not only realizes the purpose of synthesizing ferroelectrics by forming polar structures by SCSCT,but also realizes the reversibility of SCSCT,which provides ideas for the construction and exploration of new molecular ferroelectrics.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1402903)the National Natural Science Foundation of China (Grant Nos.52172116 and 62171214)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)。
文摘The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.
基金supported by the Portuguese Foundation for Science and Technology(FCT)in the framework of the Strategic Funding Contract UIDB/04650/2020 and by M-ERA.NET NanOx4EStor Contract no.M-ERA-NET3/0003/2021the Oblivion Supercomputer at university ofévora,funded by the ENGAGE SKA Research Infrastructure(reference POCI-01-0145-FEDER022217-COMPETE 2020 and FCT)+4 种基金by the BigData@UE project(reference ALT20-03-0246-FEDER-000033-FEDER and the Alentejo 2020 Regional Operational Program),for providing HPC resources in the framework of the advanced computing project CPCA/A1/415075/2021 awarded by FCT IPthe financial support through the contract FEDR-POC No.332/390008/29.122020-SMIS 109522the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposals 20202037,20202038 and 20192055supported by the COST Action CA20116-European Network for Innovative and Advanced Epitaxy(OPERA)the Royal Academy of Engineering grant,CIET1819_24,for funding and the ERC grant,EU-H2020-ERC-ADG#882929,EROS
文摘Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974307 and 61574123)Zhejiang Provincial Natural Science Foundation,China(Grant No.D19A040001)+1 种基金the Fundamental Research Funds for the Central Universities of Chinathe 2DMOST,Shenzhen University(Grant No.2018028).
文摘The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effect and ferroelectricity in group-V elemental layers,has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit.In this review,we comprehensively review recent research progress in engineering of topology and ferroelectricity,and several effective methods to control the quantum phase transition are discussed.We then introduce the coupling between topological orders and ferroelectric orders.The research directions and outlooks are discussed at the end of the perspective.It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.
基金supported by National Key Research and Development Program(grant 2019YFB2205100)National Science Foundation of China(grant 92064001)。
文摘The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future prospects for the ferroelectric HfO_(2)-based thin films and devices are presented from fundamentals to applications.The related issues are discussed,which include:1)The ferroelectric characteristics observed in HfO_(2)-based films and devices associated with the factors of dopant,strain,interface,thickness,defect,fabrication condition,and more;2)physical understanding on the observed ferroelectric behaviors by the density functional theory(DFT)-based theory calculations;3)the characterizations of microscopic and macroscopic features by transmission electron microscopes-based and electrical properties-based techniques;4)modeling and simulations,5)the performance optimizations,and 6)the applications of some ferroelectric-based devices such as ferroelectric random access memory,ferroelectric-based field effect transistors,and the ferroelectric tunnel junction for the novel information processing systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61471301,61078057,51202195,and 511172183)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20126102110045)the NPU Foundation for Fundamental Research(Grant Nos.JC201155,JC201271,and JC20120246)
文摘In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10875004 and 11005005)the National Basic Research Program of China (Grant No. 2010CB832904)
文摘5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.
基金the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20210198)the National Natural Science Foundation of China(Grant No.12204095)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2242022R10197)the National Natural Science Foundation of China(Grant No.11834002).
文摘We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarization.The first one is the orientation of polarized water molecules staying in the R2 region of SnIP.The second one is the displacement of I atom which roots from subtle interaction with absorbed water molecules.A reasonable scenario of polarization flipping is proposed in this study.In the scenario,the water molecule is rolling-up with keeping the magnitude of its electrical dipole and changing its direction,meanwhile,the displacement of I atoms is also reversed.Highly tunable polarization can be achieved by applying strain,with 26.5%of polarization enhancement by applying tensile strain,with only 4%degradation is observed with 4%compressive strain.Finally,the direct band gap is also found to be correlated with strain.
基金supported by the National Natural Science Foundation of China(Grant Nos.61471301,61078057,51172183,51402240,and 51471134)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20126102110045)+1 种基金the Natural Science Foundation of Shaanxi Province,China(Grant No.2015JQ5125)the Fundamental Research Funds for the Central Universities,China(Grant No.3102015ZY078)
文摘Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically.Magnetic frustration,which can induce ferroelectricity,gives rise to multiferroic behavior.In this paper,we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity.A disordered stacking of manganites is expected to result in frustration at interfaces.We report here that a tri-color multilayer structure comprised of non-ferroelectric La;Ca;MnO;（A）/Pr;Ca;MnO;（B）/Pr;Sr;MnO;（C） layers with the disordered arrangement of ABC-ACBCAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics.The multilayer film exhibits evidence of ferroelectricity at room temperature,thus presenting a candidate for multiferroics.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB921904 and 2012CB927402the National Natural Science Foundation of China under Grant Nos 11074142 and 11021464+1 种基金the Key Project of the Ministry of Education of China under Grant No 309003the Tsinghua TNList Cross-discipline Foundation
文摘Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ＋ is substituted with Mn2＋, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.
基金supported by the National Natural Science Foundation of China(51172291,11232015,and 11302267)the Fundamental Research Funds for the Central Universities,NCET in University+3 种基金Research Fund for the Doctoral Program of Higher EducationFok Ying Tung FoundationScience and Technology Innovation Project of Guangdong Provincial Education DepartmentGuangdong Natural Science Funds for Distinguished Young Scholar
文摘Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detected through piezoelectric force microscopy （PFM） by writing reversible ferroelectric domains. However, PLT thin film also shows off-standard ferroelectric hysteresis loops highly dependent on frequency, indicating large amount of mobile space charges in the film. Subsequent current-voltage （C-V） studies show that sandwich-like Pt／PLT／Pt structure exhibits notable bipolar resistive switching （BRS） characteristics with high stability （〉 103 switching cycles）. It is found that the C-V curves of both high- and low-resistance states have the feature of space-charge-limited current （SCLC） conduction, indicating important roles of defects in the conduction. X-ray photoelectron spectroscopy measurement further verifies that oxygen vacancies based conductive filament mechanism is likely responsible for the observed RS effect. Our demonstration of stable RS effect in the PLT thin film and its possible coupling with ferroelectricity is promising in device development and applications, such as development of ferroelectric-tunable RS memories.
文摘The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.
