Indentation Behavior of Zinc Tellurite Glasses by Using a Knoop Indenter.

Knoop hardness and the shrinkage behavior of Knoop indentation were investigated for zinc tellurite glasses. A minimum in Knoop hardness was observed at around the composition of 20ZnO⋅80TeO2. This anomalous compositional dependence originated from a decrease in coordination number of both Te and Zn with increasing in ZnO content. The decrease of four-coordinated Te results in the breakage of Te-O network. In turn, the increase of ZnO4 tetrahedra leads to the increase in covalent bonding character of the glass network. It is considered that these two effects cause the minimum of Knoop hardness. On the other hand, shrinkage of Knoop indentation in zinc tellurite glasses was observed only for the compositional range >20mol% ZnO. Considering the shrinkage of Knoop indentation as the result of a densification recovery in the glass, this compositional dependence suggests that ZnO4 tetrahedra in this glass system remarkably contribute to densification under the sharp indenter.