Linking Defect-Controlled Grain Growth and Band-Edge Optical Response in Chymosin-Assisted Pechini-Derived CeO_2-δ...

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Chemistry

Background:

• Nanocrystalline cerium dioxide (CeO2-δ) exhibits unique properties due to its small grain size and defect chemistry.
• Understanding the relationship between structural evolution and optical properties is crucial for advanced applications.

Purpose of the Study:

• To investigate the impact of grain growth, strain relaxation, and vacancy chemistry on the optical response of nanocrystalline CeO2-δ.
• To establish a quantitative link between structural and optical characteristics.

Main Methods:

• Synthesis of CeO2-δ via a chymosin-assisted Pechini route.
• Rietveld line-profile analysis for crystallite size and microstrain determination.
• Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) for defect analysis.
• Diffuse-reflectance UV-Vis spectroscopy to assess optical properties and band gap evolution.

Main Results:

• Phase-pure CeO2-δ formed between 400-1000 °C with crystallite size increasing from 3.4 to 57 nm and microstrain decreasing.
• Interface-controlled grain growth followed a normal growth law (m=2, Q≈155 kJ mol-1).
• Spectroscopic methods revealed changes in Ce3+ fraction and vacancy populations with temperature.
• A blue shift in the apparent band gap (2.78 to 2.95 eV) correlated with crystallite coarsening and Urbach energy.

Conclusions:

• Grain growth and vacancy chemistry significantly influence the near-edge optical response of CeO2-δ nanoparticles.
• The study provides a quantitative connection between structural evolution (grain size, strain, vacancies) and optical properties.
• Findings are relevant for tailoring optical characteristics of cerium dioxide nanomaterials for specific applications.