Characterization of semiconducting mixed electronic-ionic TeO2[sbnd]V2O5[sbnd]Ag2O glasses by employing ultrasonic measurements and Vicker's microhardness

Abstract

In this paper, silver tellurovanadate 40TeO2-(60-x)V2O5-xAg2O, 0 ≤ x ≤ 50 mol%, glasses (abbreviated as TVAgx) are prepared by melt-quenching to study the correlation between structural and acoustical properties of TVAgx resulting from the substitution of V2O5 by Ag2O. Elastic aspects of these glasses are investigated by measuring the longitudinal (UL) and shear (US) wave velocities using the pulse-echo overlap technique at a frequency of 5 MHz at room temperature. Ultrasonic velocities showed non-linear trends: increasing behavior for 0 ≤ x ≤ 20 mol% and decreasing trend for 20 < x ≤ 50 mol%. The structural elucidation was achieved by studying the ultrasonic wave velocities and material density at room temperature. Longitudinal modulus L, shear modulus G, Young's modulus E, bulk modulus K, Poisson's ratio σ as well as other physical properties such as Debye temperature ϴD have been determined and discussed up on the number of bonds per unit volume nb, oxygen ion packing density OPD and mean atomic volume V¯. All mentioned quantities are obtained as functions of Ag2O content, in which they show a behavior change at x = 20 mol% in excellent coincidence with the previously reported results of thermal stability (ΔT), optical band gap (Eg), and oxygen molar volume (VO*). The findings indicate the important role of non-bridging oxygens NBOs. The room temperature ultrasonic wave velocities, glass transition temperature and other mentioned quantities show a critical content of silver oxide as x = 20 mol%, indicating that the addition of a silver oxide modifier changes the compactness, rigidity and content of non-bridging oxygens (NBOs). Compositional dependence of all elastic and other mentioned properties, imply to two composition regions as: relatively strength structure for 0 ≤ x ≤ 20 and loose packing structure for 20 < x ≤ 50, which is attributed to the increase of NBOs in the second region. It is also inferred that the glass with x = 20 is more stable, in agreement with the data of calorimetric analysis. Moreover, the glass transition temperature Tg, crystallization temperature Tcr and thermal stability show a behavior change at x = 20, indicating that this glass as possess the highest thermal stability. Therefore, glass with x = 20 mol% of Ag2O has the a more rigid structure, the highest thermal stability, the highest elastic moduli, a narrower band gap, the highest OPD, and a lower VO*, which makes it an excellent and promising sample in optothermal and acousto-optic applications. Vickers microhardness of the samples vary with composition, indicating the highest value for the case of x = 20. The hardness testing results comply with those of acoustical, optical, thermal and structural tests. Also, the scanning electron microscopy (SEM) confirms the amorphous structure of the studied glasses and gives more light on their morphological aspects and their microhardness.