Effect of niobium doping on physical, thermal, and spectral parameters of infrared transmitting BGO70 glasses

Abstract

Heavy metal oxide glasses doped with 2d transition metal niobium were casted through normal melt-quench technique in the formula composition (100−x) [3Bi2O3–7GeO2 (BGO70)]−xNb2O5 where 5 ≤ x ≤ 25. Experimentally measured values of density dexp were 6.737–7.149 g/cc ± 0.06 %. Corresponding molar volume Vm exp had values 29.677–31.550 cc ± 0.04 %, Vpyc varied 32.28–34.71 cc ± 0.03 % and oxygen molar volume \( V_{{{\text{mO}}^{2-} }} \) increased linearly from 17.761 to 20.467 cc ± 0.06 %. Thermal coefficient of linear expansion was between 5.316 ± 0.001 × 10−6 and 8.033 ± 0.001 × 10−6 K−1. Glass transition temperature Tg, onset of crystallization temperature Tx, and the stability factor ΔT were noted from DTA curves. Direct allowed energy gap Eg was between 1.809–2.988 eV and Urbach energy had value 0.32–1.49 eV. Maximum transmission efficiency was 74 % for glass BGO70-Nb10. FTIR spectra revealed that lattice vibration modes were active in 400–1,300 cm−1 range. A modifying behavior was assigned to Nb5+ ion in the system.