Novel alkali-niobic bismuth germanate glass system

Abstract

Equimolar Nb2O5:Li2O co-doped BGO70 (Bi2O3:GeO2 = 30:70) glasses were prepared via melt–quench method. Their XRD pattern and nonlinear variation in thermo-physical parameters revealed structural rearrangement with increasing concentration of doped oxides and indicated ceramization of BGO glasses. Density ρ varied by 6.813–6.674 ± 0.001 g cm−3; molar volume V M (20.35–18.79) cm3 and oxygen molar volume \(V_{{{{\rm MO}}^{ - 2} }}\) (16.80–15.60) cm3 decreased monotonically. The glass transition temperature T g was between 449 and 457 ± 2 °C. Onset of crystallization temperature T x was raised from 502 to 511 ± 2 °C. Their DTA scans exposed two crystalline phases in the temperature range 25–800 ± 2 °C. The values for T p1 and T p2 observed were in the ranges 548–567 ± 2 and 671–720 ± 2 °C, respectively. Peak apex temperatures T p1, T p2 increased nonlinearly with increasing mol% of Li2O and Nb2O5 in the system. Thermal stability factor ΔT x = T x − T g indicated that all the glasses in the system are equally stable. The difference ΔT p1 = T p1 − T g resistance against crystallization had values 96–113 ± 4 °C. The thermal coefficient of linear expansion (TCE or α) for these glasses corroborated that their thermal shock resistance was increased.