Mixed alkali effect in glasses containing MnO2

Glass systems of the composition xLi2O-(25-x)K 2O-70(0.4ZnO+0.6P2O5)+5MnO2 (x = 4,8,12,16 and 20 mol ) have been prepared by melt quenching technique. The thermal and mechanical properties of the glasses have been evaluated as a function of mixed alkali content. Glass transition temperature and Vickers's hardness of the glasses show a pronounced deviation from linearity at 12 mol Li2O. Theoretically estimated elastic moduli of the glasses show small positive deviations from linearity. MAE in these properties has been attributed to the localized changes in the glass network. The absorption spectra of Mn2+ ions in these glasses showed strong broad absorption band at 514 nm corresponding to the transition 6A1g(S) â4T1g(G), characteristic of manganese ions in octahedral symmetry. The fundamental absorption edge in UV region is used to study the optical transitions and electronic band structure. From UV absorption edge, optical band gap energies have been evaluated. Band gap energies of the glasses have exhibited MAE and shows minimum value for 12 mol Li2O glass. © 2013 American Institute of Physics

Elastic properties and structural studies on lead-boro-vanadate glasses

This paper describes elastic properties and spectroscopic studies on the xPbO-50B2O3-(50 - x)V2O5 (where x = 20, 25, 30, 35, 40, 45 and 49 mol%) glass system. Elastic moduli and spectroscopic parameters exhibit compositional dependent trends and the existence of characteristic borovanadate groups in these glasses. The bulk modulus and shear modulus increase with the concentration of [BO4/2]- and [B2V2O9]2- groups, which increases the dimensionality of the network. The scheme of modification of borate and vanadate groups has been explained by considering the Sanderson's electronegativity principle. Analysis of infrared(IR) and magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectra suggests the presence of characteristic diborovanadate groups also in these glasses. The results are examined in view of the structural groups formed due to the presence of PbO as a modifier