Nanocrystalline CeO<inf>2</inf> with different particle sizes has been studied under high pressure using Raman spectroscopy techniques and diamond anvil cell at room temperature. The pressure shift of the first-order Raman frequency for each particle sizes was measured. Linear dependence of the first order Raman frequency on pressure for each particle sizes has been observed. We found that the first order Raman frequency decreases with the decreasing particle sizes under ambient condition and the lattice constant increases with the decreasing particle size. The increasing molar fraction of oxygen vacancies with the decreasing particle size is responsible for the lattice expansion.
