Mixing the starting reagents together in solution.
Removal of the solvent, leaving behind an amorphous or nano-crystaline mixture of cations and one or more of the following anions: acetate, citrate, hyroxide , oxalate, alkoxide , etc.
Heat the resulting gel or powder to induce reaction to the desired product.
The following case studies illustrate some examples of actual syntheses carried out using precursor routes.
Example:
Co-precipitation Synthesis of ZnFe2O4
Mix the oxalates of zinc and iron together in water in a 1:1 ratio. Heat to evaporate off the water, as the amount of H2O decreases a mixed Zn/Fe acetate (probably hydrated) precipitates out.
Fe2 ((COO)2) 3 + Zn(COO)2 → Fe2Zn((COO)2 )5* xH2O
After most of the water is gone, filter off the precipitate and calcine it (1000°C).
Fe2Zn((COO)2 )5 → ZnFe2O4 + 4CO + 4CO2
This method is easy and effective when it works. It is not suitable when
Reactants of comparable water solubility cannot be found.
The precipitation rates of the reactants is markedly different.
These limitations make this route unpractical for many combinations of ions. Furthermore, accurate stoichiometric ratios may not always be maintained.