研究目的
The specific objectives of this work are the determination of (i) the effect of oxygen activity on the valence of segregating chromium species and (ii) the effect of bulk composition on the segregation-induced enrichment factor of chromium in polycrystalline Cr-doped TiO2 using X-ray photoelectron spectroscopy (XPS).
研究成果
Annealing of Cr-doped TiO2 in controlled oxygen activity modifies the valence of chromium ions in the surface layer, with reducing conditions favoring Cr3+ and oxidizing conditions leading to comparable Cr3+ and Cr6+ concentrations. A theoretical model explains the segregation mechanism driven by surface charge and electric fields, highlighting the potential for tailoring surface properties for photocatalytic applications.
研究不足
The surface sensitivity of XPS for low-concentration solutes is limited, requiring complementary techniques like SIMS. The study focuses on polycrystalline specimens, and results may differ for single crystals. Defect interactions at the surface are complex and not fully characterized.
1：Experimental Design and Method Selection:
The study involves annealing Cr-doped TiO2 specimens at controlled temperatures and oxygen activities to investigate chromium segregation and valence changes. XPS and SIMS are used for surface analysis, PIXE for bulk analysis, and SEM for morphology. Theoretical models based on defect equilibria are applied.
2：Sample Selection and Data Sources:
Polycrystalline Cr-doped TiO2 specimens with chromium concentrations of 0.05, 0.15, and 1.50 at% Cr were prepared using the sol-gel method. They were sintered and annealed under various oxygen activities (e.g., pure oxygen, argon-oxygen mixtures, argon-hydrogen mixtures).
3：05, 15, and 50 at% Cr were prepared using the sol-gel method. They were sintered and annealed under various oxygen activities (e.g., pure oxygen, argon-oxygen mixtures, argon-hydrogen mixtures).
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes XPS instrument (Thermo Scientific, UK), SEM (Zeiss Ultra Plus), PIXE setup with Si(Li) detector, zirconia electrochemical oxygen probe, and materials like titanium isopropoxide and chromium chloride hexahydrate.
4：Experimental Procedures and Operational Workflow:
Specimens were annealed at 1273 K or 1373 K for specified durations in controlled oxygen environments. After annealing, surfaces were analyzed using XPS for chromium valence and concentration, SIMS for surface composition, PIXE for bulk composition, and SEM for grain size and morphology.
5：Data Analysis Methods:
XPS data were deconvoluted using casaXPS software to determine chromium species concentrations. PIXE data were analyzed with GUPIXWIN software. Statistical analysis was performed on multiple measurements to determine errors.
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