Polycrystalline molybdenum tri-oxide thin films were prepared using the spray pyrolysis
technique; a 0.1 M solution of ammonium molybdate tetra-hydrated was used as a
precursor. The samples were prepared on Corning glass substrates maintained at
temperatures ranging between 423 and 673 K. The samples were characterized through
micro Raman, X-ray diffraction, optical transmittance and DC electrical conductivity. The
species MoO3 (H2O)2 was found in the sample prepared at a substrate temperature of 423 K.
As the substrate temperature rises, the water disappears and the samples crystallize into
α-MoO3. The optical gap diminishes as the substrate temperature rises. Two electrical
transport mechanisms were found: hopping under 200 K and intrinsic conduction over
200 K. The MoO3 films’ sensitivity was analyzed for CO and H2O in the temperature range
160 to 360 K; the results indicate that CO and H2O have a reduction character. In all cases, it
was found that the sensitivity to CO is lower than that to H2O.