ATR/FTIR analysis subsequent to thermal treatment showed an evolution of the absorption bands. Heating eliminates organics residues, because the peaks at 3400 cm−1 appear as a shoulder superimposed on the O–H band. They disappear above 673 K - peak at 1700 cm−1 (j). The absorption band from 500 to 772 cm−1 decreases with the change in intensity of its components (a, b). The SnO2 modes can be seen, with the Sn-O-Sn mode at 636 cm−1, while a lattice mode of SnO2 appears at 772 cm−1.