Abstract
IR- transparent niobium substituted heavy metal oxide glass system in formula composition (100-x) BGO75- xNb2O5; 5 ≤ x ≤ 25 was fabricated by quenching and press molding technique. Glassy state was confirmed by XRD. Density ρexp varied 6.381 g/cc-7.028 g/cc ±0.06%. Modifying behavior of Nb2O5 was corroborated by rate of increase in theoretical volume Vth, measured volume Vexp and oxygen molar volume VMO -2 . Nb 5+ had larger cation radius and greater polarizing strength as compared to Ge 4+ ions. It replaced Ge 4+ sites introducing more NBOs in the network. Transformation temperatures Tg, Tx and Tp1 were 456 -469 o C ±2 o C, 516 -537 o C ±2 o C and 589 -624 o C ±2 o C respectively. In the range from room temperature to 400 o C the coefficient of linear thermal expansion α was 5.431±0.001*10 -6 K -1 to 7.333±0.001*10 -6 K -1 . ΔT = Tx-Tg and ΔTP1 = TP1-Tg varied collinearly with increase in niobium concentration and revealed thermal stability against devitrification. The direct bandgap Eg values lay in 3.24 -2.63 eV ±0.01 eV range and decreased due to impurity states of Nb 5+ within the forbidden band. Mobility edges obeyed Urbach law verifying amorphousness of the compositions. The IR-transparency window extended from 0.38 -6.1 μm in MIR which is wider than binary BGO glass as well as BGO single crystal.
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