Effects of V2O5 on elastic, structural, and optical properties of mixed ionic–electronic 20Na2O–20CaO–(60 − x)B2O3–xV2O5 glasses

Abstract

Glass samples [20Na2O–20CaO–(60 − x)B2O3–xV2O5, where 0 ≤ x ≤ 2.5 mol%] were prepared using melt-quenching method to study the mixed ionic–electronic (MIE) effect on the elastic and optical properties of the glasses. Ultrasonic velocities, elastic moduli, hardness, and Debye temperature decreased to a minimum at x = 1.5 mol%. The initial decrease in the elastic moduli may have been caused by the increase in the number of non-bridging oxygen (NBO). In this process, V2O5 acted as a modifier at low vanadium concentration but changed to a network former at x > 1.5 mol%. The FTIR spectra showed the presence of VO4, VO5, BO3, and BO4 vibration groups, and this result confirmed that V2O5 played a dual role in the glass network. Considerable decrease in dc conductivity (x = 1.5 mol%) signified a blocking effect on the ionic current in the MIE glasses. Interestingly, the observed anomaly in the elastic moduli coincided with the dc conductivity minima, indicating possible influence of the MIE effect on the elastic anomaly. Quantitative analysis using ideal bulk compression and ring deformation models showed a decrease in Kbc/Ke at x > 1.5 mol% which implies that ring deformation was reduced in the region. Furthermore, the MIE effect also influenced the optical properties of the investigated glasses. The optical band gap (E opt) and refractive index exhibited minimum and maximum values, respectively, at x = 1.5 mol%. The increase in concentration of NBOs and the defect states elucidated the significant changes in the E opt of the glasses.