Lithium niobate undergoes a slow reaction with anhydrous HF at room temperature to give LiNbOF,, which is readily hydrolysed to give Nb205 as one product. This sequence of reactions is believed to be responsible for the superior performance of aqueous alkaline silica sol modified by the addition of [HFJfor the chemomechanical polishing of LiNbO, wafers, compared with silica sol alone.