2. Experimental procedure
All reagents were used as received. Hafnium chloride (HfCl4), cerium nitrate (Ce(NO3)3⋅6H2O), citric AC 45594 (C6H8O7) and ethylene glycol (C2H6O2) were obtained from Aldrich.
2.2. Preparation of Ce-doped HfO2 nanoparticles
Pure and Ce-doped HfO2 nanoparticles with different Ce content (2.5–10% in weight) were prepared using the solgel technique. The preparation of the nanoparticles was as follows: appropriate amount of citric acid was dissolved in distilled water to prepare a clear solution. To this solution, proper amounts of hafnium chloride and cerium nitrate were added with constant stirring and ensuring a total dissolution of salts. Then, ethylene glycol was added into the mixed solution with citric acid:ethylene glycol molar ratio of 1:4. The mixture was stirred continuously at room temperature until a sol formed. The sol was evaporated 80 °C and then dried at 130 °C for 24 h in an oven to form a precursor resin. The precursor resin was transferred into a porcelain crucible and calcined at 500 and 700 °C for 2 h to decompose the organic matter completely and form the pure and Ce-doped HfO2 nanoparticles.