- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
BaWO4:Ce Single Crystals Codoped with Na Ions
摘要： Single crystals of BaWO4, BaWO4: 0.5 at. % Ce; BaWO4: 1 at. % Ce; BaWO4: 0.5 at. % Ce, 1 at. % Na; and BaWO4: 1 at. % Ce, 2 at. % Na were grown from an inductively heated iridium crucible by the Czochralski method on a Malvern MSR4 puller. They were investigated using Electron Paramagnetic Resonance (EPR) spectroscopy at helium temperatures. One isolated center of high (D2d or S4) symmetry was found and two or more other centers of lower symmetry were identified, depending on crystal doping. From the fitting using the EPR-NMR program, the following parameters of g-matrix for the high symmetry center were found: gx = 1.505, gy = 1.505, and gz = 2.731. The linewidth vs. temperature revealed an increasing exponential tendency with increasing temperature. It showed one phonon at the lower temperatures and a Raman + Orbach effect at the higher temperatures. Radioluminescence and pulse height spectra showed rather poor scintillation properties, without any contribution from cerium emission.
关键词： scheelite,EPR,local symmetry,roadmap,BaWO4,structural refinement
更新于2025-09-23 15:22:29
-
Electrochemical properties of the scheelite BaWO4 prepared by co-precipitation: Application to electro-photocatalysis of ibuprofen degradation
摘要： The scheelite BaWO4 elaborated by co-precipitation, is a wide band gap semiconductor crystallizing in the tetragonal symmetry. The oxide is identi?ed by X-ray di?raction and characterized by scanning electron microscopy and di?use re?ectance. The optical transition (2.95 eV) involves O2-: 2p orbital and W6+ eg: level, further direct transition occurs at 4.88 eV. The peaks in the Raman spectrum are assigned to symmetrical vibrations of tetragonal units [WO4]2-. The oxide shows an oxygen de?ciency and the conductivity follows a thermally activated hopping of lattice polaron with activation energy of 0.31 eV. The photo electrochemical analysis of BaWO4 at pH 5.5 gives a ?at band potential of 0.20 VSCE and electrons density of 1.8 × 1019 cm?3. The positive slope of the plot (capacitance?2 - potential) indicates n type conduction, a result con?rmed by chrono-amperometry. The frequency dispersion of the real/imaginary impedances is undertaken both in the dark and under illumination; the response is modeled by an equivalent circuit with a predominant bulk contribution. As application, the photo electrons in the conduction band (?0.11 VSCE) reduce oxygen into radicals O2?, allowing a partial mineralization of ibuprofen, one of the most consumed medicaments. The electro-photocatalysis i.e. combined electrocatalysis/electro-photocatalysis using TiPt as cathode and BaWO4 as anode (100 mA/25 V) shows a high conversion yield (75%), in aerated ibuprofen solution (20 ppm) in less than 6 h under UV light (12 mW cm?2). The reaction follows a pseudo-?rst order kinetic with a rate constant of 3.7 × 10?3 min?1, about twice higher than that obtained by electrocatalysis (50%, k = 1.9 × 10?3 min?1).
关键词： Electro-photocatalysis,Photo electrochemical,Scheelite BaWO4,UV light,Ibuprofen
更新于2025-09-09 09:28:46