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

Abstract

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.