Composition/structure relationships in monolithic borophosposilicate glasses obtained by the sol-gel route

Monolithic borophosphosilicate glasses were prepared by the sol-gel route through xerogeldensification. Tetramethoxysilane (Si(OCH3)4), trimethylborate (B(OCH3)3), and trimethylphosphite (P(OCH3)3) were used as source compounds for Si, B, and P, respectively. Afterdrying, samples underwent thermal treatment up to 700 °C with alternating flowing oxygenand reduced pressure steps, resulting in transparent, monolithic glasses. The sample chemicalcomposition was analyzed by X-ray photoelectron spectroscopy (XPS). Densification wasinvestigated by vibrational spectroscopies (FT-IR, micro-Raman). The boron oxygen holecenters (BOHC) and phosphorus oxygen hole centers (POHC) paramagnetic defects generatedby X-ray irradiation of glasses were studied by electron paramagnetic resonance (EPR)spectroscopy. The results obtained on borophosphosilicate glasses showed that paramagneticdefects are not created by independent processes, as expected for randomly distributednoninteracting B and P doping elements. Diamagnetic precursors of BOHC and POHC arethus proposed to be spatially close together in the glasses.