Effects of mixed-alkali oxides on structural, thermal, AC conductivity, dielectric and optical properties of xNa2O-(20-x)K2O-30V2O5-50TeO2 glasses / Siti Juliana Japari

Tellurovanadate glasses containing sodium and potassium oxides with
compositions xNa2O-(20-x)K2O-30V2O5-50TeO2 (x = 0-20 mol%) were prepared by
melt-quenching method to investigate the effects of mixed-alkali oxide on structural,
thermal, AC conductivity, dielectric and optical properties. Structural analysis
revealed the presence of bridging oxygen (BO) and non-bridging oxygen (NBO).
Thermal analysis results showed decrease value of glass transition temperature
from 233 °C to minimum at 227 °C (x = 10 mol%) and then increased from 235 °C to
237 °C (x ≥ 10 mol%) as Na2O content increased. The variation of AC conductivity
showed a non-linear behaviour with Na2O at temperature 383K, where
increased from 7.15 10-10 Sm-1 to maximum value at 1.40 10-9 Sm-1 (x = 15 mol%) and shifted to 1.38 10-8 Sm -1
(x = 10 mol%) at temperature 463K. Meanwhile, dielectric constant showed increase in the frequency 0.01 Hz at 2.12
10-2 Fm-1 from to a maximum at 2.55 10-2 Fm-1 (x = 10 mol%) before decreasing value at 2.37 10-2 Fm-1 to 2.47 10-2 Fm-1
(x >10 mol%) at 383 K. The maximum in the value at x = 10 mol% coincided with the anomaly. Optical band gap
showed initially decrease from 2.33 to 2.30 eV (x ≤ 10 mol%) and then
increased from 2.31 to 2.39 eV for x >10 mol%, which is suggested to be related to the
changes in concentration of non-bridging (NBO). Urbach energy behaves
inversely with . In same region (x = 10 mol%), refractive index (n) also exhibited
a maximum value at 2.77 which similar behaviour with the dielectric anomaly
indicating that NBO is more polarizable on the properties.