Effect of TiO2 substitution on optical and structural aspects of phosphate glasses

• Incorporation of TiO2 leads to depolymerisation of POP network, thus forming more stable and strong POTi bonds.
• The increase in TiO2 content improves the strength of phosphate glass network.
• Q1 structural units increase at the expense of Q2 structural units with substitution of TiO2.

Transparent bubble free phosphate glass samples having composition 50P2O55Al2O320CaO(25 − x)Na2OxTiO2 with x varying from 0 to 12.5 mol% were synthesized using conventional melt quench technique. X-ray diffraction patterns confirmed the amorphous nature of prepared glass samples. The density and hence the strength of the prepared glasses increases with the doping of TiO2 at the expense of Na2O while the molar volume follows the reverse trend. The direct and indirect optical band gap energies were found to decrease with the addition of TiO2 and the refractive index as calculated from the Lorentz equations was observed to follow the opposite trend. This trend shows that these glasses are potential candidates for non linear optical devices. FTIR and Raman spectra depicts that the main structural units present in the prepared glasses are (PO2)−, (PO3)2−, (PO4)3−. With the addition of TiO2, Q1 dominates the glass network and is accompanied with a few Q0 and Q2 tetrahedral units. Addition of TiO2 to the host glass composition creates a stronger POTi bonding to substitute POP and OPO bonds as is evidenced by the Raman spectra. Thus addition of TiO2 in the glass composition shows a systematic trend in the enhancement of glass network.

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