**2.5 Pechini method**

Pechini method is a widely used method consisting of the mix of metal nitrate solution of the starting materials with a stoichiometric amount of citric acid. The resulting solution is stirred on a hot plate and the temperature stabilized at about 90ºC, at which point ethylene glycol is added at a mass ratio of 40:60 with respect to citric acid. The temperature is maintained constant up to the resin formation, which polymerizes at about 300ºC. The precursor powders are heated for several hours at various temperatures.

This method, as a soft-chemistry one, leads to homogeneous and low crystalline products at relatively low temperatures, but they usually require expensive initial compounds and/or complicated synthesis procedures.
