Radial Distribution Function of amorphous silicon oxycarbide compounds

The short-range order in silicon oxycarbide materials was investigated after extraction of the Radial Distribution Function from X-Ray diffraction patterns (MoK alpha, lambda = 0.7107 Angstrom). The samples were made by sol-gel method, using a mixture of two precursors: methyldiethoxysilane HSi(OEt)(2)CH3 (MDES) and triethoxysilane HSi(OEt)(3) (TREOS). After drying, the gels were pyrolysed at 1000 degrees C under inert atmosphere to form a single amorphous phase. The structural evolution according to three different compositions was investigated: i) a silicon oxycarbide network with excess of C; ii) the stoichiometric SiCxO2(1-x) where x = 0.3, and iii) the silicon oxycarbide network poor in C, i.e., with excess of Si. The results obtained from glasses were compared to RDF of amorphous compounds in the system Si-C-O. The examination of the short-range order in the first neighbor shell showed that the main network is made of SiO4 and SiCO3 tetrahedral units with an average first nearest neighbor distance around 1.65 Angstrom and an average bond angle near to 134 degrees.