The invention provides compositions and methods for planarizing or polishing a surface. One composition comprises about 0.01 wt. % to about 20 wt. % α-alumina particles, wherein the α-alumina particles have an average diameter of 200 nm or less, and 80% of the α-alumina particles have a diameter of about 500 nm or less, an organic acid, a corrosion inhibitor, and water. Another composition comprises α-alumina particles, an organic acid, dual corrosion inhibitors of triazole and benzotriazole, wherein the wt. % ratio of the triazole to benzotriazole is about 0.1 to about 4.8, and water.