Sol-gel synthesis of humidity-sensitive P2O5-SiO2 amorphous films

The sol-gel synthesis of silicophosphate gels using phosphoryl chloride and tetraethoxysilane as molecular precursors is reported and discussed. Gel-derived glasses and films having the molar compositions 10P(2)O(5) . 90SiO(2) and 30P(2)O(5) . 70SiO(2) have been obtained. The structure of the dried gels as well as the structural modifications that occurs during the transformations in gel-derived glasses are analyzed by Fourier transform infrared spectroscopy (FTIR). It has been found that the evidence of the P-O-Si linkages begins to appear only on the FTIR spectra of the bulk gels heat treated up to 400 degrees C while they are well resolved on the FTIR spectra of the bulk gel samples heated up to 1000 degrees C indicating that at this temperature the transformation in the corresponding gel-derived glasses occurs. The humidity sensitive properties of the gel-films have been evaluated by electrochemical impedance spectroscopy (EIS). The phosphorous content as well as the temperature of the heat treatments strongly affect the sensitivity to RH of the gel-derived films.