Investigation of non-bridging oxygen formation and structural evolution in SrO-doped borosilicate glasses

Abstract This study investigates the structural modifications and crystallization behavior of glasses in the system xSrO–(40 − x)SiO 2 –30CaO–30B 2 O 3 (x = 0, 10, 20, 30, 35 mol%). The amorphous nature of as-prepared glasses was confirmed through X-ray diffraction analysis. Upon thermal treatment, controlled crystallization led to the formation of apatite, wollastonite, and strontium silicate crystalline phases, as evidenced by XRD and TEM analyses. The progressive substitution of SrO for SiO 2 resulted in increased concentration of non-bridging oxygen atoms (NBO) in both silicate (SiO 4 ) and borate (BO 4 ) structural units, as revealed by FTIR and NMR spectroscopy. The presence of NBOs promoted crystallization processes and facilitated the formation of nano-crystalline species. The formation of biocompatible crystalline phases, particularly wollastonite (CaSiO 3 ) and apatite (CaSrBO 4 ), suggests potential applications in orthodontic and orthopedic fields.