Structural Properties and Nonstoichiometric Behavior of CeO

Dipartimento di Scienze e Tecnologie Chimiche, Universitd di Udine, via Cotonificio 108, 33100 Udine, Italy e-mail trovarelli dstc.uniud.it 

Reduced ceria results from the removal of O ions from the CeOj lattice, which generates an anion vacant site according to the following scheme  

Some complications were introduced into the system in this composition region by Ricken et al. and Riess et al. , who confirmed the previously suggested stoichiometries at n=7,10 and 11 but also found stable phases at an oxygen-cerium ratios of 1.808 (Pi) and 1.79 (P2). At the same time, Knappe and Eyring confirmed the existence of phases at n=7 and 11 (not 9 and 10) by electron microscopy and determined two new phases at n=19 ( 619034) and n=62 (06520,12) as well as a series of other less clearly defined phases in the range CeO, 1.76 x 1.79. These compositions closely correspond to the ones reported independently by Ricken et al.. Recently, the crystal structures of Ce70i2 and Cei,02o have been confirmed by refinement of syngle crystal neutron diffraction data.  

At an 0/Ce ratio lower than 1.714, the Ce02 phase diagram is dominated at high temperature by the presence of the a phase, a non-stoichiometric (Ce203+8) phase 

21 or 11.26 A calculated and found respectively for C-type 6303. In another study, the stabilisation of nanosize particles of ceria as cubic 6203 was suggested on the basis of calculation of the lattice parameter of ceria sols having diameter of a few nanometers. The decrease of particle size strongly stabilised Ce ion, and the extrapolation of lattice parameter values suggested that the C-type sesquioxide exists when constituted by nanoparticles of diameter less than 1.5nm, with most of Ce 

---