Manganese modified structural and optical properties of bismuth silicate glasses

• SiO2 is present in SiO4 tetrahedral structural units with two NBOs per silicon.
• Conversion of BiO3 structural units into BiO6 units with increase in MnO2.
• MnO2 acts as network modifier and exists in MnO6 structural units.
• On addition of MnO2, Bi–O–Si linkages are replaced by Bi–O–Mn linkages.

Glass system with compositions xMnO2–(60−x) Bi2O3–40SiO2 have been synthesized by standard melt quench technique. X-ray diffraction patterns confirm the amorphous nature of as-prepared glass samples. The values of density have been measured and molar volume determined is found to decrease with increase in MnO2 content. Theoretical calculations of crystalline volume (Vc) have also been made. The glass transition temperature (Tg) determined using differential scanning calorimetry (DSC) is observed to increase with increase in MnO2 content. The structural analysis has been carried out using FTIR and Raman spectroscopy. In the present glass system, MnO2 acts as network modifier and exists in MnO6 structural units. Bismuth acts both as network former with BiO3 pyramidal units as well as network modifier with BiO6 octahedral units in the present glass system. SiO2 exists in form of SiO4 tetrahedral structural units with two non-bridging oxygens (NBO’s). The optical band gap energy (Eg) has been estimated from Tauc’s plot for direct transitions, it decreases with increase in manganese content.

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