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Non‐Stoichiometry Induced Switching Behavior of Ferroelectric Photovoltaic Effect in BaTiO <sub/>3</sub> Ceramics
摘要： Ferroelectric photovoltaic (FPV) effect has been studied among a series of non-stoichiometric BaTiO3 (Ba/Ti ? 0.92–1.05) ceramic chips prepared by tape casting method. The FPV performance increases abruptly when the Ba/Ti molar ratio deviates from the stoichiometry within 1%. Meanwhile, a photocurrent direction switching behavior is observed between Ti-excess and Ba-excess samples. The TEM analysis shows their significant difference in grain-boundary (GB), where abnormal GB with a width of 10–15 nm is observed in Ba-excess sample. The photocurrent switching phenomenon is described to the competition between the asymmetrical Schottky barriers induced PV effect and intrinsic FPV effect. Widen GB in Ba-excess BaTiO3 ceramics restrains the intrinsic FPV effect and results in the switching behavior. This study offers direct evidence of the vital role of GB in FPV effect and may promote the development of photovoltaic devices.
关键词： ferroelectric photovoltaic,barium titanate,non-stoichiometry,switching behavior
更新于2025-11-21 11:03:13
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Thinning ferroelectric films for high-efficiency photovoltaics based on the Schottky barrier effect
摘要： Achieving high power conversion efficiencies (PCEs) in ferroelectric photovoltaics (PVs) is a longstanding challenge. Although recently ferroelectric thick films, composite films, and bulk crystals have all been demonstrated to exhibit PCEs >1%, these systems still suffer from severe recombination because of the fundamentally low conductivities of ferroelectrics. Further improvement of PCEs may therefore rely on thickness reduction if the reduced recombination could overcompensate for the loss in light absorption. Here, a PCE of up to 2.49% (under 365-nm ultraviolet illumination) was demonstrated in a 12-nm Pb(Zr0.2Ti0.8)O3 (PZT) ultrathin film. The strategy to realize such a high PCE consists of reducing the film thickness to be comparable with the depletion width, which can simultaneously suppress recombination and lower the series resistance. The basis of our strategy lies in the fact that the PV effect originates from the interfacial Schottky barriers, which is revealed by measuring and modeling the thickness-dependent PV characteristics. In addition, the Schottky barrier parameters (particularly the depletion width) are evaluated by investigating the thickness-dependent ferroelectric, dielectric and conduction properties. Our study therefore provides an effective strategy to obtain high-efficiency ferroelectric PVs and demonstrates the great potential of ferroelectrics for use in ultrathin-film PV devices.
关键词： power conversion efficiency,Schottky barrier effect,ferroelectric photovoltaics,PZT ultrathin film,depletion width
更新于2025-11-14 17:28:48
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[Lecture Notes in Mechanical Engineering] Advances in Thin Films, Nanostructured Materials, and Coatings (Selected Papers from the 2018 International Conference on “Nanomaterials: Applications & Properties”) || Stain Effect on the Properties of Polar Dielectric Thin Films
摘要： Low cost scalable processing and substrates are critical for optimized polar dielectric performance of functional oxide thin ?lms if they are to achieve commercialization. Here, we present a comprehensive investigation of the role low-cost MgO, Al2O3, SrTiO3 and Si substrates on the structural and electrical properties of sol-gel derived SrTiO3 (ST) and K0.5Na0.5NbO3 (KNN) thin ?lms. The substrate is found to have a strong effect on the stress/stain state and, consequently, on the dielectric and ferroelectric response of the ?lms. A tensile stress induced in-plane by the thermal expansion mismatch between the substrates and the ?lms observed for ST and KNN ?lms deposited on platinized Al2O3 and Si substrates, respectively, lowers the relative permittivity and remanent polarization values in the parallel plate capacitor geometry. In contrast, a compressive stress/strain observed for ST ?lms deposited on MgO/Pt and KNN ?lms on SrTiO3/Pt substrates result in superior polarization and dielectric permittivity, corresponding to enhanced out-of-plane displacement of Ti4+ ions in ST ?lms and Nb5+ ions in KNN ?lms. It is thus demonstrated that for polycrystalline polar dielectric thin ?lms the relative permittivity and polarization may be optimized through an induced compressive stress state.
关键词： Dielectric properties,Sol-gel,Thin ?lms,Stress/strain,Thermal expansion,Ferroelectric hysteresis
更新于2025-11-14 17:28:48
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Dielectric tunable properties of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics prepared by spark plasma sintering
摘要： Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were prepared by spark plasma sintering (SPS) technique and their phase composition, microstructures and dielectric tunable properties were studied. With increasing Mg2TiO4?MgO content, the dielectric peaks of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics were broadened and suppressed. The tunability of Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics first increased and then decreased with the increase of Mg2TiO4?MgO content. For Mg2TiO4?MgO content ≤ 50 wt%, Ba0.5Sr0.5TiO3?Mg2TiO4?MgO composite ceramics showed higher tunability and lower permittivity than pure Ba0.5Sr0.5TiO3, which can be attributed to the suppression of the doping effect by SPS. The contradiction between reduced permittivity and enhanced tunability in ferroelectric-dielectric composites was resolved.
关键词： Dielectrics,Ferroelectric ceramics,Spark plasma sintering,Composites
更新于2025-11-14 17:28:48
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Defect dipole evolution and its impact on the ferroelectric properties of Fe-doped KTN single crystals
摘要： The ferroelectric and piezoelectric properties of doped potassium tantalum niobate crystals with different Fe doping amounts and the adjustability of the properties are investigated. The hysteresis loops and current density curves show that the defect dipoles have an obvious effect on domain reorientation, and the effect decreases with increasing doping amount. The ferroelectric and piezoelectric properties can be adjusted via the defect dipoles, and the adjustability is reduced with increasing doping amount. A change of the doping amount leads to defect dipole structure evolution in the crystals, in which the defect dipoles transform from a polar structure to a nonpolar structure, which is the reason for the transition of the domain reorientation determined by the defect dipoles. This result has proved that introducing defects is an effective way to improve and regulate perovskite properties, and the doping amount is one of the important factors controlling the defect dipoles.
关键词： Ferroelectric,domain orientation mechanism,defect dipoles,doping behavior
更新于2025-11-14 17:28:48
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Origin of giant negative piezoelectricity in a layered van der Waals ferroelectric
摘要： Recent research on piezoelectric materials is predominantly devoted to enhancing the piezoelectric coefficient, but overlooks its sign, largely because almost all of them exhibit positive longitudinal piezoelectricity. The only experimentally known exception is ferroelectric polymer poly(vinylidene fluoride) and its copolymers, which condense via weak van der Waals (vdW) interaction and show negative piezoelectricity. Here we report quantitative determination of giant intrinsic negative longitudinal piezoelectricity and electrostriction in another class of vdW solids—two-dimensional (2D) layered ferroelectric CuInP2S6. With the help of single crystal x-ray crystallography and density-functional theory calculations, we unravel the atomistic origin of negative piezoelectricity in this system, which arises from the large displacive instability of Cu ions coupled with its reduced lattice dimensionality. Furthermore, the sizable piezoelectric response and negligible substrate clamping effect of the 2D vdW piezoelectric materials warrant their great potential in nanoscale, flexible electromechanical devices.
关键词： 2D materials,CuInP2S6,negative piezoelectricity,electrostriction,van der Waals ferroelectric
更新于2025-11-14 17:28:48
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Phase-transition induced giant negative electrocaloric effect in a lead-free relaxor ferroelectric thin film
摘要： Ferroelectric/antiferroelectric thin/thick films with large positive or negative electrocaloric (EC) effects could be very useful in designing commercial refrigeration devices. Here, a giant negative EC effect (maximum ΔT ≈ ?42.5 K with ΔS ≈ ?29.3 J K?1 kg?1) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 (BCT–BMT) lead-free relaxor ferroelectric thin films prepared on Pt(111)/TiOx/SiO2/Si substrates using a sol–gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane [111] direction plays a very key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by ingeniously utilizing and combining both the giant negative and positive EC effects. Moreover, a large energy density of 51.7 J cm?3 with a high power density of 1.15 × 1010 W kg?1 at room temperature is also achieved in the thin film, indicating that it is also an attractive multifunctional material for energy storage.
关键词： lead-free,energy storage,electrocaloric effect,phase transition,thin film,relaxor ferroelectric
更新于2025-11-14 17:28:48
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Upconversion photoluminescence modulation by electric field poling in Er3+ doped (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 piezoelectric ceramics
摘要： Luminescent piezoelectric materials promise a stratagem for controlling the optical process by electric field, which would benefit for future optoelectronic devices. Here, Er3+ doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT: Er3+) piezoelectric ceramics are prepared to demonstrate the proof of concept. In addition to excellent intrinsic piezoelectricity and ferroelectricity, BCZT: Er3+ ceramics exhibit simultaneously strong green upconversion emissions under excitation of 980 nm. Remarkable photoluminescence (PL) quenching phenomenon as well as significant changes on relative intensities of stark lines are observed under external poling electric field. Furthermore, field dependent piezoelectric constant d33 and photoluminescence quenching ratio show similar variation trend and finally saturate for E>3.5 kV/mm, which provides a noncontact strategy to monitor the piezoelectric constant d33. The PL quenching triggered by electric field in BCZT: Er3+ ceramics is ascribed to the decreased asymmetry originating from field-induced structural transformation from a significant fraction of the tetragonal phase to rhombohedral phase. Our work would be helpful for expanding the scope of luminescent piezoelectric materials and promising future optoelectronic and optical devices with cross-coupled physical properties.
关键词： Piezoelectric,Electric field poling,Photoluminescence,Ferroelectric polarization
更新于2025-11-14 15:28:36
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Enhanced visible-light-driven photocatalytic activity of BiFeO3 via electric-field control of spontaneous polarization
摘要： Well-polarized BiFeO3 nanoparticles have been successfully prepared by a facile electrical poling method with the assist of a soluble organic-inorganic composite film. From XRD, TEM and SEM studies, no significant change in the crystal structure or morphology was detected after the electrical poling process. The visible-light driven photocatalytic process of poled BiFeO3 nanoparticles was accelerated by 2 times compared to unpoled BiFeO3. By combining time-resolved photoluminescence (PL), photoinduced silver deposition testing and photoelectrochemical measurements, it can be revealed that the enhanced photocatalytic performance of poled samples can be properly attributed to the promoted separation and prolonged lifetime of the photogenerated carriers caused by the ferroelectric polarization. These findings may offer a new route to promote the photocatalytic or photoelectric performances of BiFeO3 for advanced applications by adjusting the ferroelectric polarization.
关键词： BiFeO3 nanoparticles,Organic-inorganic composite film,Ferroelectric polarization,Electrical poling technology,Photocatalytic activity
更新于2025-11-14 15:24:45
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Electroresistance of Pt/BaTiO<sub>3</sub>/LaNiO<sub>3</sub> ferroelectric tunnel junctions and its dependence on BaTiO<sub>3</sub> thickness
摘要： Recently, ferroelectric tunnel junctions (FTJs) have attracted considerable attention due to their great potential in next generation non-volatile memories. In this work, we report on thickness-dependent tunneling electroresistance (TER) and corresponding evolution of transport behavior in Pt/BaTiO3/LaNiO3 FTJs with various BaTiO3 thicknesses of 2.0, 3.2, and 4.8 nm. The TER effect is observed in the 3.2 nm-thick Pt/BaTiO3/LaNiO3 tunnel junction and an ON/OFF current ratio of ~170 is achieved due to the modulation of barrier height by polarization reversal. When the BaTiO3 is increased to 4.8 nm in thickness, the ferroelectric-modulation of the barrier profile becomes more pronounced and the dominant transport mechanism changes from electron tunneling to thermally-activated thermionic injection. As a result, the OFF state current is significantly reduced due to the suppression of the Fowler-Nordheim tunneling with increased width and height of the BaTiO3 barrier. A greatly improved ON/OFF current ratio of ~12500 is thus achieved in the 4.8 nm-thick Pt/BaTiO3/LaNiO3 FTJ device. These results facilitate deeper understanding of the TER effects from the viewpoint of not only the barrier profile but also the transport mechanism.
关键词： Pulsed laser deposition,Ferroelectric tunnel junctions,Ferroelectric memory,Resistive switching
更新于2025-09-23 15:23:52