Effect of melt temperature on the structure of BaO–TiO2–GeO2 glass

We have examined the dependence of the structure of BaO–TiO2–GeO2 (BTG) glass on the temperature at which the BTG glass melt is held in the molten state (called the “melt temperature” in the present paper). The absorption coefficient and refractive index of the BTG glass increase with increasing melt temperature because of the reductive conditions. During melting at 1550 °C, Ti3+ and GeE′ centers are generated together with the formation of TiO5 units. We conclude that the yellow coloration observed in the BTG glass prepared at higher melt temperatures is due to the generated Ge2+. It is expected that the local structures of the glass generated at high melt temperatures will affect the crystallization behavior to increase the second-order optical nonlinearity of the glass–ceramic material.