Tuning Oxygen Vacancies and Microstrain in CeO2 Nanoparticles: A Raman-Based Synthesis–Property Map for Rare-Earth Catalysis

Cerium oxide (CeO2) is a key rare-earth material for catalysis and energy applications, yet quantitative links between synthesis parameters, morphology, and defect chemistry remain scarce. Using three selected conditions from a broader synthesis matrix with octadecylamine (ODA) concentration (0.01–0.2 M) and ethanol/water ratio (α = 0.3–3.0), we obtained three distinct morphologies: spherulites (CeO2-AA), short nanorods (CeO2-BB), and long rods (CeO2-MM). CeO2-BB nanorods exhibit the highest BET surface area (79.9 m2/g), Ce3+ content (30.2%), and Odef/Olat ratio (0.99), while CeO2-MM shows an Odef/Olat ratio of 0.80. A controlled comparison with commercial 25 nm CeO2 (similar crystallite size, 21.3 nm, but 60× lower microstrain) reveals that, within the investigated sample set, microstrain and defect-related disorder are the dominant contributors to Raman F2g broadening, rather than phonon confinement. The ID/IF2g ratio correlates strongly with Ce3+ content (R2 = 0.94), supporting Raman as a sensitive indicator of defect-related disorder or oxygen-vacancy-associated defects. Qualitative inspection of the data suggests that ODA concentration has a more pronounced influence on aspect ratio, Ce3+ content, and bandgap than the ethanol/water ratio, although the limited number of synthesis conditions precludes definitive statistical ranking. This integrated framework enables rational design of CeO2 nanostructures with tailored defect chemistry for catalysis and rare-earth-based applications.