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.sub.(1-x)Ti.sub.(x)O.sub.2, 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.sub.(1-y)Ce.sub.(y)O.sub.2, where y is .ltoreq.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. The agglomerates can be used as an abrasive material in chemical mechanical polishing compositions to remove film layers during the fabrication of integrated circuit devices.