We describe a simple, non-destructive method, in situ thermală ellipsometry analysis (TEA), for understanding the different processesă (decomposition of organics, crystallization, and sintering) occurringă upon heating hybrid organic-inorganic films. According to these studies,ă a thermal treatment was tailored in order to obtain robust,ă nanocrystalline inorganic mesoporous 100-150 nm thick films withă efficiently connected porosity surrounded by a crystalline inorganică network. Polymodal porous, nanocrystalline NiO/Gd-doped Ceria compositesă or Ni/Gd-doped Ceria films, interconnected network of open pores rangingă from macro- to micro-pores, have been synthesized. The inorganic networkă is built from connected crystalline nanoparticles with mean diameters ofă 12 +/- 3 nm, whose small size is still preserved even at 800 degrees C.ă We also show that the thermal ellipsometry analysis is readilyă extendable to MO/Gd-doped Ceria with M - Cu, Ni, Co, etc., thereforeă demonstrating the interest of this technique in understanding thermală phenomena in complex ceramic and composite systems. This is trivial foră designing electrodes with efficient microstructure.