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

• Copper–lead and copper–zinc borate glasses are studied for relations between structure and mechanical properties.
• Cations are used to tailor the intermediate-range speciation of borate groups.
• Zinc metaborates show a high disproportionation tendency of the metaborate group.
• In both glass types, the addition of copper oxide results in a more homogenous network of [BØ2O]- and [BØ4]-metaborate units.

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.