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Novel photo-voltaic device based on Bi1?xLaxFeO3 perovskite films with higher efficiency
摘要： Photovoltaic cells using polycrystalline La substituted bismuth iron oxide, Bi1?xLaxFeO3, (0.1 ≤ x ≤ 0.4), films as the light harvesting component were investigated in this work. A novel cell set-up utilizing a double layered TiO2 film as top contact and a thin layer of quasi-solid polymer electrolyte as back contact was used and a significant enhancement in cell efficiency was observed for assemblies based on x ≥ 0.2 samples, coincident with a structural transition of Bi1?xLaxFeO3 from ferroelectric to non-ferroelectric. The power conversion efficiency of the PV device was 0.13% for the cell with x = 0.2 at 1 sun irradiation. The short circuit current density for this La composition was 0.35 mA cm?2. A hysteretic behaviour was observed for higher La compositions when the scanning is from open-circuit (OP) to short-circuit (SC) which may be attributed to polarization effects. The results at x ≥ 0.2 show an improved performance with respect to BiFeO3 based systems, suggesting the stabilization of the non-ferroelectric crystal structure leads either to a more efficient separation of photo-generated electron–hole pairs and/or enhanced charge transport. The findings represent a step towards the realisation of facile to fabricate, inorganic solid state photovoltaic devices.
关键词： ferroelectric,Photovoltaic cells,power conversion efficiency,quasi-solid polymer electrolyte,Bi1?xLaxFeO3,non-ferroelectric,TiO2
更新于2025-09-10 09:29:36
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Understanding and predicting geometrical constraint ferroelectric charged domain walls in a BiFeO <sub/>3</sub> island via phase-field simulations
摘要： It has been known that ferroelectric charged domain walls (CDWs), which break the polarization continuity, may be electrically active with an elevated conductivity. However, the bound charge at CDWs may render them energetically unstable, and thus, forming CDWs naturally and manipulating them electrically is still challenging. Here, we theoretically utilize phase-field simulations to design spontaneously generated CDWs with center-type quad-domains in a single square-shaped BiFeO3 nanoisland. It is shown that the stability of the spontaneously emerging head-to-head domain walls with center-convergent quad-domains is mainly determined by three contributions, namely, the geometrical constraint from approximately 45°-tilted bottom edges, the electric boundary condition, and the necessary screening free charges to compensate head-to-head domain walls. It is demonstrated that the center-convergent quad-domains with head-to-head CDWs can be electrically switched to the center-divergent one with tail-to-tail CDWs, providing guidance for achieving ferroelectric domain-wall-based nanodevices with low-power dissipation.
关键词： phase-field simulations,electric boundary condition,ferroelectric charged domain walls,BiFeO3,screening free charges,geometrical constraint
更新于2025-09-10 09:29:36
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Effective dielectric tensor of deformed-helix ferroelectric liquid crystals with subwavelength pitch and large tilt angle
摘要： Short pitch deformed helix ferroelectric liquid crystals have numerous applications as active materials in displays, optical telemetry, and biomedical devices. In this paper, we derive convenient analytical formulas to calculate the effective dielectric tensor of these materials beyond the space average approximation. By comparison with exact numerical calculations, we show that our formulas are remarkably accurate in predicting optical properties in virtually all practical situations, including the important case of large tilt angles, where the space average approximation breaks down. We also present a comparison between the two complementary approaches of expanding the mesoscopic dielectric tensor versus the mesoscopic transfer matrix, by deriving an expression for the effective transfer matrix as an in?nite expansion and explicitly calculating the corresponding effective dielectric tensor for the ?rst time. Our results demonstrate that both methods give accurate predictions when two-photon scattering terms are taken into account.
关键词： deformed-helix ferroelectric liquid crystals,space average approximation,effective dielectric tensor,two-photon scattering,optical properties
更新于2025-09-10 09:29:36
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Improvement of ferroelectric random access memory manufacturing margin by employing Pt/AlO <i> <sub/>x</sub></i> bottom electrode for the La-doped Pb(Zr,Ti)O <sub/>3</sub> ferroelectric capacitor
摘要： In our previous works on La-doped Pb(Zr,Ti)O3 (PLZT) growth on a Pt/Ti bottom electrode, the O2 content in postdeposition annealing (PDA) was found to play an important role in obtaining good electrical characteristics and high manufacturing yield of ferroelectric random access memory (FeRAM). The optimal O2 content of around 2% inhibits the growth of randomly oriented La-doped Pb(Zr,Ti)O3 (PLZT) grains near the PLZT surface, resulting in the growth of highly {111}-oriented PLZT. We found that the Pt bottom electrode grown on an AlOx layer can further suppress the formation of randomly oriented PLZT grains near the PLZT surface and increases the optimal O2 content range from 2 to 50%, which can enlarge the manufacturing process margin of PDA. It is proven that the AlOx layer blocks the di?usion of lead oxides (PbOx) from PLZT to SiO2 interlayers through Pt and promotes pyrochlore-perovskite transformation near the bottom electrode during PDA.
关键词： ferroelectric random access memory,bottom electrode,postdeposition annealing,PLZT,manufacturing margin
更新于2025-09-10 09:29:36
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Influence of additives on structure and ferroelectric properties of NBT-BT-BMT ceramics
摘要： Influence of various over stoichiometric additives on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of solid solutions 0.8[0.8(Na0.5Bi0.5)TiO3-0.2BaTiO3]-0.2Bi(Mg0.5Ti0.5)O3 system has been studied. The unit cell volume slightly decreased in case of the V2O5 additives but did not change in case of Bi2O3, LiF, and KCl additives. Increase in dielectric parameters ert and tandrt values at the room temperature was revealed for compositions doped by KCl additives, while these parameters decreased in compositions doped by the V2O5 additives. Linear correlation between piezoelectric coefficient d33 measured for separate grains using the Piezoresponse Force Microscopy method and dielectric permittivity ert values at the room temperature was confirmed.
关键词： ferroelectric phase transitions,additives,dielectric properties,perovskite structure,Ceramics (Na0.5Bi0.5)TiO3 - BaTiO3 - Bi(Mg0.5Ti0.5)O3
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Accurate Measurement at the Nanoscale of Remnant Polarisation Charge in Ferroelectric Films
摘要： A method for the measurement of the remnant polarisation charge of ferroelectric ?lms at the nanoscale is proposed. It is based on current measurement by an atomic force microscope and imposes a capacitive correction in order to extract the signal from the noise, several orders of magnitude higher than the signal to be measured. A remnant charge of 4.2 fC could be measured on a PbZrTiO3 thin ?lm. Solutions to decrease the noise are proposed.
关键词： ferroelectric materials,remnant polarisation,nanoscale current measurement,Atomic Force Microscopy
更新于2025-09-10 09:29:36
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P-12.2: Active Matrix Field Sequential Color Electrically Suppressed Helix Ferroelectric Liquid Crystal for High Resolution Displays
摘要： In this article, we disclose a 3-inch 250ppi active matrix field sequential color electrically suppressed ferroelectric liquid crystal (ESHFLC) display. ESHFLC’s ultra-fast response time (~10μs at 6.67V/μm) enables the display resolution to be tripled via field sequential color technique. Photo-alignment technology provides ESHFLC with optimal anchoring energy which contributes to a high contrast ratio over 10K:1. Specific 3T1C pixel circuit is designed to convert the analog signal to pulse width modulation. Thus the field sequential color ESHFLC display is achieved on LTPS TFT panel. With the delivered prototype, we successfully demonstrate the active matrix FSC ESHFLC integrated display system. We believe this display may replace IPS or FFS in the near future for portable mobile market. Moreover, high resolution FSC ESHFLC can find more applications in emerging virtual reality displays.
关键词： Active Matrix Field Sequential Color,Fast Response,Ferroelectric Liquid Crystal Displays,Virtual Reality
更新于2025-09-10 09:29:36
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Effect of cobalt substitution on the multiferroic characteristics of ferroelectric potassium sodium niobate (K0.5Na0.5NbO3) ceramics
摘要： The room-temperature multiferroic behavior of cobalt-substituted KNN [K0.5Na0.5Nb1?xCoxO3, 0.02 ≤ x ≤ 0.05] ceramics has been investigated. Both the X-ray diffraction and selected area electron diffraction analysis confirm that all the compositions found to be crystallized in the single phase (Orthorhombic, Amm2) without any formation of cobalt clusters and/or other secondary phases such as Co3O4. Co2+ oxidation state and the presence of oxygen vacancies in the samples have been studied through X-ray photoelectron spectroscopic measurements. The changes in the bandgap with the increase of Co concentration in KNN are noticed from UV–Visible absorption spectroscopy. Magnetic measurement on the samples reveals a dominant antiferromagnetic interaction attributed to the Co2+–Co2+ exchange interactions via F0-center and coupling between Co2+–Co2+ through O2?. The existence of exchange bias (EB) effect is also observed in KNaNb1?xCoxO3 (x = 0.03, 0.04, 0.05) samples from the magnetic measurements. In addition, it is found that defect complexes formed between Co′′′ Nb and oxygen vacancy lead to the enhanced dielectric, ferro, and piezoelectric properties of K0.5Na0.5Nb1?xCoxO3 ceramics.
关键词： Multiferroic,Cobalt-substituted KNN,Ferroelectric,Exchange bias,Antiferromagnetic
更新于2025-09-10 09:29:36
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Structural, bulk permittivity and impedance spectra of electronic material: Bi(Fe0.5La0.5)O3
摘要： In the present paper, fabrication and characterization (structural, electrical and ferroelectric properties) of a lead-free lanthanum (La) modified bismuth ferrite electroceramic having composition Bi(Fe0.5La0.5)O3 (BFLO) using various experimental techniques have been reported. BFLO has been synthesized by means of a high-temperature inter-diffusion of oxides method. This investigation mainly aims to correlate the phase formation and physical properties while the Fe-site of bismuth ferrite has partially been replaced by La. The surface micrograph shows the formation of the high dense ceramic sample. Analysis of data of various complex spectroscopies related to modulus and impedance exhibits the relaxation mechanism in this sample is of non-Debye type. The combined effect of grains and grain boundaries has been depicted from the Nyquist plot through the least-squares fitting of suitable circuit model along with the experimental data. The remnant polarization and coercive field decreases as temperature rises which was discerned from the ferroelectric loop obtained at different temperatures. The existence of ferroelectric nature in the sample was postulated from the polarization versus electric field plot.
关键词： Ferroelectric properties,Non-Debye relaxation,Lanthanum modification,Bismuth ferrite,Electroceramic
更新于2025-09-10 09:29:36
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Two-level hierarchical stripe domains and enhanced piezoelectricity of rapid hot-press sintered BiFeO <sub/>3</sub> ceramics
摘要： BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples.
关键词： ferroelectric,hot-press sintering,BiFeO3,multiferroic,domain structure,piezoelectric
更新于2025-09-10 09:29:36