Thermal evolution of sol–gel-obtained phosphosilicate solids (SiPO)

Amorphous phosphosilicate solid with P–O–Si linkages was obtained by a sol–gel process starting from tetraethoxysilane (TEOS) and H3PO4. The evolution of the structure of as-prepared gel was investigated as a function of the heat-treatment temperatures, by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectra (XPS) studies. XPS reveals that the surface of the particles is poorer in Si than the bulk at low temperatures. Heating the gel allows its crystallisation through the formation of Si–O–P linkages at the expends of the Si–O–Si and P–O–P networks, while an enrichment of silicium at the surface is detected.