The use of mixed cerium-containing synthetic solid abrasive materials in chemical mechanical polishing slurries can provide better selectivity, better substrate removal rates, or lower defect rates than conventional ceria slurries. The slurries have abrasive particles that include a plurality of solid cerium-containing phases selected from CeO.sub.2, Ce.sub.2O.sub.3, cerium-nitride material, cerium-fluoride material, and cerium-sulfide material, where different cerium-containing materials are present in different particles or on the same particles.