A cubic form of Ce2O3 (C-type) might also coexist in the nanocrystalline form where the oxidation state of Ce is +3 rather than +2. This occurs due to the increased amount of oxygen vacancies (Vo) on lowering the dimension to the nanoscale. The percentage of Ce +3 and Vo gets intensified a lot at the nanoscale. There is an increase in the lattice parameter of CeO2 particles of different sizes as shown in the diagram (Fig2a) The unit cell of CeO2 with space group Fm-3m is given in the inset. The abnormality in the expansion occurs in a certain temperature range as shown by the blue region in which at about 50 o C, CeO2 of all dimensions show the same lattice parameter. The most intense peak in the diffraction pattern on ceria occurring with h k l value as (1 1 1) also changes its angle of occurrence with a change in temperature (Fig ). A reversible tetragonal (P42/nmc) to cubic (Fm-3m) phase transition in nanosized ceria, which triggers negative thermal expansion in the temperature range of (-25 °C-75 °C )has been reported [37-39].