The influence of germanate anomaly on elastic moduli and Debye temperature behavior of xLi2O-(100 − x)[0.65GeO2·0.35PbO] glass system

Alkali-germanate glass composed of xLi2O-(100 − x)[0.65GeO2·0.35PbO] (x = 0 mol% to 40 mol%) were prepared using the melt-quenching method. The increase in density to a maximum at x = 10 mol% before decreasing indicates presence of the germanate anomaly. Both longitudinal and shear velocities, as well as both independent longitudinal (CL) and shear (μ) moduli, also showed similar non-linear behaviors, with maximum values at x = 10 mol%. The increase in independent moduli at x < 10 mol% is suggested to be related to the germanate anomaly, in which formation of smaller three-membered GeO4 rings connected to [GeO6]2− units leads to an increase in the rigidity and stiffness of the glass network. Meanwhile, the decrease in the elastic moduli for x > 20 mol% is suggested to be due to weakening of the glass network by progressive depolymerization of three-membered GeO4 rings in the germanate network through formation of non-bridging oxygen. In addition, bulk modulus, Ke, Young's modulus, and Debye temperature also showed similar behaviors as CL and μ. Analysis using bulk compression and ring deformation models showed the ratio of theoretical Ke over experimental Kbc and average ring size were also affected by the germanate anomaly, and the closest to ideal isotropic compression was at x = 10 mol%.