**2.4 Freeze-drying technique**

In the freeze drying method, standardized nitrate solutions were mixed according to the stoichiometry of the final products: Nd0.8Sr0.2(Mn1-xCox)O3 (x = 0.1, 0.2 and 0.3). The starting materials were Nd2O3 (99.9%) which had to be dissolved in diluted nitric acid before the addition of the other compound; Sr(NO3)2 (99%); Co(NO3)2.6H2O (99%) and Mn(C2H3O2)2.4H2O (99 %).

The mixture for freeze-drying method was frozen drop-by-drop under liquid nitrogen and subjected to freeze drying at P = 5.10-2 mbar. Thermal decomposition was achieved by slow heating in air up to 600ºC. The pure phases were obtained after repeated heatings at 850ºC (with intermediate grindings), each of 10 h, under nitrogen atmosphere. A flow chart for this method is shown in Figure 1d.
