Compositional design for SrTiO3 crystal precipitation from spinodal-type borosilicate glass containing large amounts of TiO2

B2O–SiO2 borosilicate glasses in a specific composition range show a spinodal-type phase separation by heat-treatment at around those glass transition temperatures, and porous glasses or porous glass-ceramics can be easily obtained via an acid treatment after the phase separation. We have studied preparation conditions of SrTiO3-precipitated porous glass-ceramics for a photocatalyst of hydrogen generation using solar energy. It was found that the SrTiO3 crystal was observed for a SrO–BaO–TiO2–SiO2 glass, while the SrTiO3 crystal disappeared from SrO–TiO2–B2O3–SiO2 glasses, which contain the B2O3 component necessary for the phase separation. For this problem, we found that co-doping of K2O and Al2O3 components is effective, and a SrTiO3 containing porous glass-ceramic was successfully obtained by the co-doping. Molecular dynamics (MD) simulations were performed to understand the migration of Sr2+ ions in SrO–TiO2–B2O3–SiO2 glasses with K2O and Al2O3 components. This paper is the first to describe the dynamics of alkali metal/alkaline earth metal ions in those glasses and the mechanism of SrTiO3 precipitation in borosilicate glasses.