Structure and mechanical properties of copper-lead and copper-zinc borate glasses

Copper-lead and copper-zinc borate glasses with different copper contents were prepared and studied for correlations between structure and mechanical properties, where the cations are used to tailor the intermediate-range speciation of borate groups. Structural characterization was done by optical absorption, electron spin resonance (ESR), Raman and infrared (IR) spectroscopy. The mechanical properties were investigated through in-depth instrumented indentation and mechanical resonance analyses. The zinc metaborate glass series shows a high disproportionation of metaborate into mainly trigonal pyroborate [B2O5](4-) and polyborate [Bempty set(3)](0) units, while the lead borate glass series exhibits a network based on trigonal [Bempty set(2)O](-) and tetrahedral [Bempty set(4)](-) metaborate units and a minor PbO-pseudophase(empty set = bridging oxygen and O = non-bridging oxygen). For both glass types, the addition of copper oxide results in a more homogenous network containing [Bempty set(2)O](-) and [Bempty set(4)](-) metaborate units. This induces an enhancement of the elastic moduli and hardness in the lead borate glass series, but a decrease of these properties in the copper-zinc borate glasses, whereby copper-zinc borate glasses are stiffer and harder than copper-lead borate glasses. (C) 2015 Elsevier B.V. All rights reserved.