Formation of an amorphous product phase during the solid state reaction between a vitreous SiO2 thin film and a (001) BaTiO3 substrate

The solid state chemical reaction of a thin SiO2 film with a single-crystal (001) BaTiO3 substrate has been investigated as a model system for processes occurring during the sintering of BaTiO3 ceramics with the sintering additive SiO2. Thin amorphous SiO2 films on (001) BaTiO3 substrates react with the substrate during annealing at 1000°C for 5 to 15 min. Transmission electron microscopy (TEM) has revealed the formation of a glassy reaction product after 5 min of heating. The composition of this glass has been analyzed by energy dispersive X-ray spectrometry (EDX), showing mainly SiO2 and about 16 at.% of BaTiO3. The Ba:Ti ratio of the glass is 1:1. During prolonged heating, or if the initial BaTiO3 surface is decorated with Pt markers, the reaction product crystallizes, with the fresnoite Ba2TiSi2O8 forming as the dominant crystalline phase.