Abstract: The present invention provides substantially spherical composite ceria/titania particles, a method of forming the same, and chemical mechanical polishing compositions comprising such particles. The substantially spherical particles include a substantially crystalline core portion including one or more crystallites having a cubic lattice structure including Ce(1-x)Ti(x)O2, where x is <0.25, and a substantially amorphous cladding covering at least a portion of the substantially crystalline core portion, the substantially amorphous cladding including Ti(1-y)Ce(y)O2, where y is ?0.50. The method of forming the particles includes combusting an organic solvent including a cerium salt of a carboxylic acid and a titanium (IV) chelate in a combustion supporting gas and collecting agglomerates comprising two or more substantially spherical particles.