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Multi-doped bismuth ferrite thin films with enhanced multiferroic properties
摘要： Thin films of multi-doped bismuth ferrite, Bi0.97?xLaxSr0.03Fe0.94Mn0.04Co0.02O3 (BLxSFMC, x = 0.00–0.18), are synthesized on a fluorine-doped tin oxide (FTO)/glass substrate. The structure and multiferroic properties of the film samples are characterized and tested. The results indicate that on doping, the structure of the BLxSFMC film changes has been changed. The concentrations of both oxygen vacancies and Fe2+ are decreased. The BL0.18SFMC thin film exhibits Ohmic conduction, which reduces the influence of the built-in electric field Ebi of the space-charge region at the interface between an Au electrode and the BLxSFMC during polarization. The BL0.18SFMC thin film also exhibits enhanced ferroelectric properties than the undoped film, with a higher residual polarization of 188 μC/cm2 and a higher squareness ratio of 1.21. Meanwhile, the reduced number of oxygen vacancies also reduces the Fe2+/Fe3+ ratio, thereby enhancing the Dzyaloshinskii–Moriya interaction of Fe–O–Fe bonds, and so the BL0.18SFMC thin film exhibits enhanced ferromagnetism, with a saturation magnetization of Ms ≈ 3.94 emu/cm3. Thus, multi-ion doping can improve both the ferroelectric and ferromagnetic properties of BLxSFMC thin films.
关键词： Ohmic conduction,built-in electric field,oxygen vacancy,multiferroic
更新于2025-11-14 17:28:48
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Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution
摘要： This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO6 octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi4Ti2.98W0.01Nb0.01O12 possesses an optimum piezoelectric coefficient (d33) of 32 pC/N, a high Tc of 655 °C and a large resistivity of 3 × 106 Ω·cm at 500 °C. The maximum d33 reported here is approximately quadruple than that of pure BIT (~7 pC/N). Moreover, the d33 of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.
关键词： Bi4Ti3O12,Structure distortion,Piezoelectric properties,Oxygen vacancy,Temperature stability
更新于2025-09-23 15:23:52
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Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO <sub/>2</sub> Thin Films
摘要： Vanadium dioxide (VO2) is a strongly-correlated material with 3d-electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron-correlations. These ultrathin (~10 nm) epitaxial VO2 films were grown on NiO (111)/Al2O3 (0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies (x~0.20±0.02) into the VO2-x system via annealing under high vacuum (~5x10-7 Torr) and elevated temperature (450 oC). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V-V vibrational modes and stabilization of V-V dimers are observed in vacuum-annealed VO2 films providing conclusive evidence for stabilization of monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2-x thin films resulting in the metallic character at room temperature. With these results, we propose a defect engineering driven pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2.
关键词： Defect engineering,Oxygen Vacancy,Metallicity,Mott transition,Metallic monoclinic VO2,Charge doping
更新于2025-09-23 15:23:52
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CO and H2 activation over g-ZnO layers and w-ZnO(0001)
摘要： Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111) and their reactivities towards CO and H2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystal. The interaction and reaction between CO/H2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS) and Density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface towards CO and H2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared inert at below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces towards CO could be related to the formation energy of oxygen vacancy (EOvf), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.
关键词： CO oxidation,NAP-STM,ZnO,XPS,surface polarity,oxygen vacancy
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP) - Hiroshima (2018.5.27-2018.6.1)] 2018 IEEE ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP) - Control of Leakage Current through BaTiO<inf>3</inf> Film by Cumulative Cycle of Applied Voltage Scanning for ReRAM or Neuromorphic Application
摘要： We found a new phenomenon that shows a large change in leakage current through BaTiO3 (BTO) film with the maximum ratio of 107 to 109 observed in this work by changing cumulative cycle of voltage scan applied on the film capacitor. These leakage phenomena are thought to depend on several factors such as BTO film thickness, concentration of Vo+, bias voltage, its sweep rate and so on, because trapping/detrapping of carrier electron into/from oxygen vacancy would be a competition dependent on their rates and concentrations. These results imply that the leakage current can be controlled by some sequences or protocols of applied voltage scan, leading to use for ReRAM or neuromorphic applications.
关键词： ReRAM,leakage current,resistive switching,BaTiO3,oxygen vacancy
更新于2025-09-23 15:23:52
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Local structural changes due to the electric field-induced migration of oxygen vacancies at Fe-doped SrTiO <sub/>3</sub> interfaces
摘要： We report on our study of dc voltage-induced structural changes at reduced and oxidized Fe-doped SrTiO3 (Fe:STO) electrode interfaces using second harmonic generation (SHG) together with photoluminescence (PL) method. We show that oxygen vacancy defects play a critical role in determining the local electrical and structural properties of interfacial depletion regions at Schottky junctions. The SHG results show that the dc electric field causes oxygen ions and vacancies to displace toward the anode and cathode in the low field regime, respectively. This process forms electrostrictive distortions within local interfacial depletion regions which are described by Fe:Ti-O bond stretching and bending. Differences in the EFISHG responses from the oxidized and reduced crystal interfaces are explained according to local oxygen vacancy concentrations and dynamics and their effects on the Schottky barrier heights and depletion region widths at each interface. These results are further supported by our PL measurements. Oxygen ion migration towards the Fe:STO surface leads to enhanced fluorescence intensities from in-gap acceptor states. We demonstrate that SHG and PL measurements are well suited for understanding and resolving the underlying causes of dielectric breakdown processes and device failure brought on by dc electric field and ionic defect migrations in perovskite-type electroceramics.
关键词： Photoluminescence,Oxygen Vacancy,Electroceramic,Second Harmonic Generation
更新于2025-09-23 15:23:52
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Removal of tetracycline by BiOBr microspheres with oxygen vacancies: Combination of adsorption and photocatalysis
摘要： Oxygen vacancy-containing BiOBr microspheres with dual functions of adsorption-photocatalysis were synthesized by a simple solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR) and UV–vis diffuse reflectance spectroscopy (DRS). BiOBr microspheres with oxygen vacancies exhibited a higher adsorptive and photocatalytic activity for the removal of tetracycline (TC) than that of defect-deficient BiOBr microspheres. After adsorption for 30 min and visible light irradiation for 90 min, about 94 % of TC was removed by oxygen vacancy-containing BiOBr microspheres, and TC removal efficiency performed effectively in a wide pH range from 3.1 to 11.00. Almost all inorganic anions, such as Cl?, SO2?4, PO3?4, CO2?3 and NO?3, inhibited the removal of TC by BiOBr microspheres and their inhibition effects followed the order of PO3?4 > SO2?4 > CO2?3 > Cl? > NO?3. The surface hydroxyl groups had no effect on TC adsorption, and the adsorption of TC on BiOBr was mainly through the anion exchange process. The existence of oxygen vacancies facilitated the generation of superoxide radicals (O2??), which were the dominant reactive oxygen species for TC degradation in BiOBr suspension. The adsorptive and photocatalytic performance of oxygen vacancy-containing BiOBr decreased to different degrees after three cycles mainly due to the formation of surface complex.
关键词： Mechanism,Photocatalysis,Oxygen vacancy,Adsorption,BiOBr microspheres,Tetracycline
更新于2025-09-23 15:23:52
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Improved charge separation of NiS nanoparticles modified defect-engineered black TiO2 hollow nanotubes for boosting solar-driven photocatalytic H2 evolution
摘要： NiS nanoparticles (NPs) modified black TiO2 hollow nanotubes (NBTNs) are successfully synthesized via surface hydrogenation and facile solvothermal method. The unique structure with intensified surface and interface characteristic endow NBTNs with more catalytic sites, and increase charge carrier separation efficiency with a extended charge lifetime, overwhelmingly promoting its photocatalytic performance. The resultant NBTNs possess a relatively high surface area and pore size of ~89 m2 g-1 and ~9.8 nm, respectively. The resultants NBTNs exhibit an excellent solar-driven photocatalytic hydrogen rate (3.17 mmol h-1 g-1), which almost as high as that of Pt as cocatalyst, in which the apparent quantum (AQE) yield of 5.4 % (420 nm) is recorded for the NBTNs sample. Moreover, the turnover number (TON) can be up to 116000 within 48 h. And the turnover frequency (TOF) is 2400 for NiS. This novel strategy could provide a better understanding of cocatalyst photocatalytic mechanism, and a scheme simultaneously regulating the morphology and structure of photocatalyst for promoting H2 generation.
关键词： Mesoporous TiO2 nanotube,Oxygen vacancy defect,NiS cocatalyst,Photocatalysis,Ti3+ self-doping
更新于2025-09-23 15:23:52
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Enhanced Solar Conversion of CO <sub/>2</sub> to CO Using Mn-doped TiO <sub/>2</sub> Based on Photo-thermochemical Cycle
摘要： Photo-thermochemical cycle (PTC) is a promising method to converting CO2 to solar fuels. To study the mechanism of CO2 reduction based on PTC, sol-gel synthesized titanium dioxide (ST) and Mn-doped TiO2 (MT) films were produced and applied to the PTC under simulated solar light irradiation. Commercial P25 (PT) was used as a reference. Experiments show that Mn-doped TiO2 produced more CO than undoped TiO2 and P25. The average CO production of 1.0 wt% MT by the PTC was 32.19 μmol?m?2?h?1, 4.36 times than that of ST and 3.63 times that of PT. Various characterization methods were conducted to investigated the effect of Mn ions doping on the photo-response and charge transfer of samples. Density functional theory (DFT) calculations were also performed to verify the analysis and enhance the PTC mechanism. In conclusion, several key factors that Mn ions promote CO2 conversion have been clarified.
关键词： Oxygen vacancy,Mn doping,DFT calculation,CO2 reduction,Photo-thermochemical cycle
更新于2025-09-23 15:22:29
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Hierarchical porous TiO2 single crystals templated from partly glassified polystyrene
摘要： Hierarchical macro-mesoporous anatase TiO2 single crystal is one-pot synthesized in an EtOH-H2O system using polystyrene (PS) as the single porogen both for macropore and mesopore and TiF4 as the titanium precursor. The key to the simultaneous growth of single crystal and the introduction of hierarchical pores is the assembly of PS and titania at the glassification temperature of PS (100 °C). During the hydrolytic polymerization of TiF4, PS is encapsulated inside titania and gradually glassified. The interference from elastic PS on the oriental growth of TiO2 crystallite is thus minimized and the final removal of PS through calcination leaves interconnected macropore and mesopore inside the single crystal. According to XPS, EPR and fluorescence analyses, abundant oxygen vacancies are formed on the hierarchical porous single crystal, which presents extraordinary photocatalytic activity and stability in degrading organic pollutants under simulated sunlight irradiation using Rhodamine B as the model. The improved photocatalytic activity is a synergistic effect of improved separation of charge carrier and facilitated interfacial charge transfer benefitting from highly accessible porous single crystal structure.
关键词： Oxygen vacancy,Photocatalysis,Single crystal,Charge transfer,Hierarchical porous TiO2
更新于2025-09-23 15:22:29