Elastic and structural changes of xNa2O–(35 − x)V2O5–65TeO2 glass system with increasing sodium

• Elastic properties and structure of xNa2O–(35 − x)V2O5–65TeO2 glasses were studied.
• Ultrasonic velocities and related elastic moduli showed large decrease for x > 15 mol%.
• Polaronic–ionic transition was earlier reported in the same region.
• Raman spectroscopy showed large increase in non-bridging oxygen.
• Ratio of Kbc/Ke indicates main mechanism is isotropic compression.

Sodium vanadotellurite glass system with composition xNa2O–(35 − x)V2O5–65TeO2; (x = 5–25 mol%) was prepared by melt-quenching method. Elastic moduli and structural changes were studied by measuring ultrasonic shear and longitudinal velocities using the pulse-echo–overlap technique and Raman spectroscopy, respectively. Both shear and longitudinal velocities showed small steady decrease with addition of Na2O from x = 5 mol% to x = 15 mol% followed by large decrease at x > 15 mol%. Longitudinal modulus (CL), shear modulus (μ), Young's modulus (Y), Hardness (H) and Debye Temperature (θD) also showed similar behaviour to the ultrasonic velocities. The decrease in elastic moduli is suggested to be due to weakening of network rigidity of the glass system with increase in formation of non-bridging oxygen, NBO as revealed by Raman spectroscopy. Additional analysis using bulk compression and ring deformation models showed that ratio between theoretical bulk modulus, Kbc and experimental bulk modulus, Ke was around 2.1 for x = 5–20 mol% before an increase to around 2.4 for x > 20 mol% indicating that the main compression mechanism is ideal isotropic compression.