- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Oxygen vacancy induced photoconductivity enhancement in Bi <sub/> 1- <i>x</i> </sub> Ca <i> <sub/>x</sub></i> FeO <sub/>3-δ</sub> nanoparticle ceramics: A combined experimental and theoretical study
摘要： Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca2+ at Bi3+ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi1-xCaxFeO3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca2+ concentration which signi?es the role of OV. A signi?cant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that OV at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2–4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk OV are nearly ?at, degenerate, and discrete, the defect states due to surface OV are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to signi?cant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells.
关键词： density functional theory,BiFeO3,spark plasma sintering,Ca doping,oxygen vacancies,photoconductivity
更新于2025-09-11 14:15:04
-
Synthesis Structural and Optical Properties Of (Co, Al) co-doped ZnO Nano Particles
摘要： We prepared (Co, Al) co-doped ZnO nanostructures using the method chemical co-precipitation successfully, at room temperature using PEG (Poly ethylene glycol) as stabilizing agent. Samples are prepared with different concentrations by keeping aluminium at 5 mol percent constant and varying the concentration of cobalt from 1 to 5 mol percent. After the preparation all the samples are carefully subjected to characterizations such as XRD, SEM with EDS, TEM, PL and UV-VIS-NIR. XRD pattern shows that all the samples possess hexagonal wurtzite crystal structure having no secondary phases pertaining to Al or cobalt, which shows successful dissolution of the dopents. TEM results shows the accurate size of particles and is confirmed the XRD data. SEM images of all the samples shows that particles are in nearly spherical shape, EDS spectrum reveals that incorporation of cobalt and aluminum in host lattice. PL spectrum shows that all the samples containing two prominent peaks centered at 420 nm and 446 nm. UV-VIS-NIR spectra has shown three absorptions peaks in the range of wavelength 550 nm to 700 nm, which are ascribed as typical d-d transitions of cobalt ions.
关键词： UV-VIS-NIR,Zinc vacancies,Oxygen vacancies,Local transitions and Poly ethylene glycol.
更新于2025-09-10 09:29:36
-
Photocatalytic decomposition of methanol-water solution over N-La/TiO2 photocatalysts
摘要： Manuscript focuses on the role of N-doping on photocatalytic behaviour of N-La/TiO2 materials in decomposition of methanol-water solution. N-La/TiO2 materials were prepared with approximately the same amounts of La (0.14–0.16 wt%) and di?erent amounts of N (0.33–0.97 at. % of surface nitrogen). Addition of small amount of surface nitrogen signi?cantly increased the amount of hydrogen produced for N-La/TiO2 photocatalysts in contrast to TiO2 and La/TiO2. The chemical composition (XRF, AAS, XPS), structural (XRD, Raman, XPS, TEM), textural (N2-adsorption) and optical properties (DRS) were studied. N-La/TiO2 materials showed approximately the same speci?c surface area and crystallite size, with values ranging for La/TiO2 and N/TiO2 photocatalysts. For studied N-La/TiO2 photocatalysts, the photocatalytic activity increased with the increasing amount of surface nitrogen (interstitial positions, XPS), and subsequently with increasing amount of oxygen vacancies (Raman spectroscopy) and decreasing amount of surface oxygen species (surface lattice O species and hydroxyl groups evidenced by XPS).
关键词： Surface oxygen species,N-La/TiO2,Oxygen vacancies,Hydrogen production
更新于2025-09-10 09:29:36
-
Influence of Oxygen Vacancy Density on the Polaronic Configuration in Rutile
摘要： Polaronic con?gurations that were introduced by oxygen vacancy in rutile TiO2 crystal have been studied by the DFT + U method. It is found that the building block of TiO6 will expand when extra electron is trapped in the central Ti atom as polaron. With manually adjusting the initial geometry of oxygen vacancy structure, a variety of polaronic con?gurations are obtained after variable-cell relaxation. By calculating different sizes of supercell model, it is found that the most stable con?guration can be in?uenced by the density of oxygen vacancy. With increasing interaction between vacancies, the most stable polaronic con?guration change from small polaronic con?guration to mixed con?guration.
关键词： DFT + U,rutile,electronic structure,oxygen vacancies,polarons
更新于2025-09-10 09:29:36
-
Enhanced Photocatalytic Response of N Doped Niobium Titanates Prepared by Ion Exchange Process
摘要： Herein we report the homogeneous and effective substitution of O by N in the layered titanates. The resultant materials HTiNbO5-xNx (350°C, 30 min) unveiled extraordinary band-to-band excitation and intensity (induced by oxygen vacancies). Upward shift of valence band maximum by N 2p states is confirmed by photoelectron spectroscopy and is concluded as the source of band-to-band visible light excitation. The electrons generated upon visible light excitation in the conduction band of HTiNbO5-xNx (350°C, 30 min) had strong reduction ability, reducing O2 into active O2?- radicals during photocatalysis. These findings are the clear evidence for the substantial role of doped N in achieving band-to-band visible-light photon excitation in layered titanates. The new physical insights into substitutional N in layered titanates with hydrogen bond (weak bond energy) gained here may have important implications for developing other efficient visible light photocatalysts by nonmetal doping.
关键词： Oxygen vacancies,Band-to-band excitation,Active O2?- radicals,Substitutional N
更新于2025-09-10 09:29:36
-
Visible-light-driven CeO2/black phosphorus heterostructure with enhanced photocatalytic performance
摘要： CeO2/black phosphorus (BP) heterostructure nanocomposite was synthesized via a two-step assembly method. The structure and optical property of the prepared composites were characterized by X-ray diffraction, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Photocatalytic degradation of bisphenol A (BPA) in simulated waste water was performed by using CeO2/BP nanocomposite as catalyst. Results indicated that the degradation rate of BPA reached 82.3% within 180 min, which was remarkably improved compared with pure CeO2 and BP due to the formation of indirect Z-scheme heterostructure intermediated by oxygen vacancies originated from CeO2. The unique heterostructure facilitated the charge transfer and preserved the high redox potential leading to improve the photocatalytic degradation performance.
关键词： photocatalytic degradation,heterostructure,bisphenol A,oxygen vacancies,CeO2/black phosphorus
更新于2025-09-10 09:29:36
-
Role of oxygen vacancies in Co/Ni Substituted CeO2: A comparative study
摘要： Single phase Co/Ni substituted CeO2 nanoparticles reveal the importance of oxygen vacancies on the electronic properties of the materials. The effect of Co/Ni substitution on the structural, optical, and photoluminescence properties of CeO2 have been studied systematically. Lattice shrinks and hence strain increase owing to incorporation of Co/Ni in CeO2. Optical absorption analysis shows a red shift in band-gap with Co/Ni substitution. Photoluminescence studies reveals increase in defect concentration which causes quenching of PL emission. Vibration-modes at ~460 cm-1 in Raman spectra indicates incorporation of Co/Ni in CeO2 lattice whereas a broad peak appearing at ~ 540-640 cm-1 with substitution depicts the defects related to the increase in oxygen vacancy. X-ray absorption (XAS) studies show that Co/Ni substitution maintains local structure while Ce4+ → Ce3+ concentration increases to preserve the charge neutrality in lattice.
关键词： Oxygen vacancies.,Strain,Bandgap,Urbach energy,Cerium oxide
更新于2025-09-10 09:29:36
-
Effect of SrTiO <sub/>3</sub> oxygen vacancies on the conductivity of LaTiO <sub/>3</sub> /SrTiO <sub/>3</sub> heterostructures
摘要： In this work, we report the formation of a conductive layer through oxygen vacancies in an underlying SrTiO3 (STO) layer due to the growth of LaTiO3 (LTO) and the resulting LTO thickness-dependent conductivity of the LTO/STO system. Crystalline LTO films were grown by molecular beam epitaxy on TiO2-terminated STO(001) single-crystal substrates and 8-unit-cell (u.c.) STO template layers grown on Ge(001), under partial pressures of molecular oxygen ranging from 10?10 to 10?7 Torr. Film crystallinity was studied by in situ reflection high-energy electron diffraction, ex situ X-ray diffraction, and ex situ transmission electron microscopy. Film composition and the existence of oxygen vacancies were confirmed by in situ X-ray photoelectron spectroscopy. LTO films grown on STO substrates at oxygen partial pressures of 10?10 Torr were optimally oxidized (1:1:3 La:Ti:O). However, LTO films grown on 8-u.c. templates of STO on Ge with oxygen partial pressures less than 10?7 Torr showed extensive reduction of the Ti oxide and desorption of Sr/SrO in the STO layer. LTO films began to over-oxidize when grown on STO single-crystal substrates at oxygen partial pressures greater than 10?10 Torr but were nearly optimally oxidized when grown on STO templates on Ge at oxygen partial pressures of 10?7 Torr. Electrical characterization showed a dependence of conductivity on the thickness of the LTO films, with sheet carrier densities reaching ～5 × 1016 cm?2 for 20-u.c. (8-nm-thick) LTO/STO grown at 10?10 Torr of oxygen, suggesting that significant conduction occurred throughout the STO substrate due to the formation of oxygen vacancies.
关键词： oxygen vacancies,conductivity,SrTiO3,molecular beam epitaxy,LaTiO3/SrTiO3 heterostructures
更新于2025-09-10 09:29:36
-
Effects of ultraviolet photon irradiation and subsequent thermal treatments on solution-processed amorphous indium gallium zinc oxide thin films
摘要： Effects of exposure to ultraviolet (UV) photons and thermal treatments on solution-processed amorphous indium gallium zinc oxide (a-IGZO) films were investigated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. As a result, oxygen vacancies obviously become more abundant in the films sintered at 250 or 300 ?C by the exposure to 7.21 eV photons and less abundant by the subsequent thermal treatment at 250 ?C in air. The drain current also clearly becomes smaller in a thin film transistor fabricated using the IGZO film in a manner opposite to the abundance of oxygen vacancies. That is, the drain current becomes smaller by the UV irradiation and returns to the original high value by the subsequent thermal treatment. This indicates that oxygen vacancies act as trapping centers or scattering centers of electrons. In addition, the reversible change of the drain current with the cycle of UV irradiation and the thermal treatment opens the possibility of the use of the IGZO films as a UV sensor.
关键词： oxygen vacancies,amorphous indium gallium zinc oxide,thin film transistor,UV irradiation,thermal treatment
更新于2025-09-10 09:29:36
-
Electronic Structure and Band Alignment of LaMnO <sub/>3</sub> /SrTiO <sub/>3</sub> Polar/Nonpolar Heterojunctions
摘要： The behavior of polar LaMnO3 (LMO) thin films deposited epitaxially on nonpolar SrTiO3(001) (STO) is dictated by both the LMO/STO band alignment and the chemistry of the Mn cation. Using in situ X-ray photoelectron spectroscopy, the valence band offset (VBO) of LMO/STO heterojunctions is directly measured as a function of thickness, and found that the VBO is 2.5 eV for thicker (≥3 u.c.) films. No evidence of a built-in electric field in LMO films of any thickness is found. Measurements of the Mn valence by Mn L-edge X-ray absorption spectroscopy and by spatially resolved electron energy loss spectra in scanning transmission electron microscopy images reveal that Mn2+ is present at the LMO surface, but not at the LMO/STO interface. These results are corroborated by density functional theory simulations that confirm a VBO of ≈2.5 eV for both ideal and intermixed interfaces. A model is proposed for the behavior of polar/nonpolar LMO/STO heterojunctions in which the polar catastrophe is alleviated by the formation of oxygen vacancies at the LMO surface.
关键词： oxygen vacancies,LaMnO3,SrTiO3,polar/nonpolar heterojunctions,valence band offset
更新于2025-09-09 09:28:46