Ceria-zirconia
Ceria-zirconia is a solid solution of cerium(IV) oxide and zirconium oxide.
Crystal Structure and Stability
The crystal structure adopted by ceria-zirconia depends on the Zr/Ce ratio and temperature. At very low Zr concentrations, ceria-zirconia exhibits the cubic fluorite structure, which is common to both pure ceria and cubic zirconia. However, at higher Zr contents, other crystal structures are formed, including two different tetragonal phases at intermediate Zr concentrations, and a monoclinic phase at very high Zr concentrations.There is both experimental and theoretical evidence showing that the decomposition of ceria-zirconia into Ce-rich and Zr-rich oxides is thermodynamically favorable in a wide range of solid solution compositions, indicating that ceria-zirconia is metastable with respect to phase separation.