Precursors for sol-gel preparations

Precursors used for the synthesis of oxide systems by the sol-gel method are reviewed and their role in the various stages of the process is discussed. Emphasis is given to alkoxide precursors and to their physical and chemical properties. In particular, the following topics are discussed: degree of oligomerization, volatility, viscosity, reactions with alcohol, molecular association between alkoxides, hydrolysis, stabilization against hydrolysis. Some information about preparation methods, commercial products and availability is also given. Among non-alkoxide precursors, nitrates, carboxylates, acetylacetonates, chlorides and other inorganics are described from the point of view of their use in sol-gel preparations. They are compared, when possible, with the corresponding alkoxides.