Effect of small additions of Li 2 O on phase separation and crystallization of barium‐silicate glasses

It is known that the addition of Li 2 O to 33.3BaO‐66.7SiO 2 glass, whose composition is the same as BaSi 2 O 5 , promotes crystallization of BaSi 2 O 5 . In this study, in order to clarify the effect of a smaller amount of Li 2 O, x Li 2 O‐(30‐ x )BaO‐70SiO 2 [mol%] ( x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high‐BaSi 2 O 5 and low‐BaSi 2 O 5 which transformed from high‐BaSi 2 O 5 . It is found that the introduction of only 0.2 mol% and 0.5 mol% Li 2 O significantly changes the crystallization behavior. In the composition without Li 2 O, only high‐BaSi 2 O 5 was formed after heat treatment even for 24 h. For compositions containing Li 2 O, low‐BaSi 2 O 5 was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li 2 O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si‐rich droplet phases and Ba‐rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi 2 O 5 , suggesting a significant change in crystallization behavior.