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

Abstract : 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 [BØ3]0 units, while the lead borate glass series exhibits a network based on trigonal [BØ2O]− and tetrahedral [BØ4]− metaborate units and a minor PbO-pseudophase (Ø = bridging oxygen and O = non-bridging oxygen). For both glass types, the addition of copper oxide results in a more homogenous network containing [BØ2O]− and [BØ4]− 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