Vickers nanoindentation hardness and deformation energy of transparent erbium tellurite nanocrystallized glasses

Transparent nanocrystallized glasses consisting of Er₂Te₅O₁₃ nanocrystals (∼100 nm size) have been prepared in 10BaO·10Er₂O₃·80TeO₂, and load/unload displacement curves at room temperature (humidity 53%) have been measured in the penetration depth of h_t=200-600 nm using a Vickers nanoindentation technique. The values (4.0-9.4±0.1 GPa) of universal (dynamic) hardness (H_u) in the nanocrystallized glasses are larger than those (H_u=2.7-6.5±0.1 GPa) in the precursor glass and are slightly smaller than those (H_u=4.4-9.7±0.1 GPa) in the opaque crystallized glass consisting of Er₂TeO₆ crystals. The elastic recoveries during unloading are 0.53-0.61, being almost the same as those in the precursor and opaque crystallized glasses. The elastic U_e and plastic U_p deformation energies at h_t=500 nm in the nanocrystallized glasses are estimated to be U_e=106 and U_p=91±3 kJmol^-1, respectively. These values are larger than those of the precursor glass (U_e=83 and U_p=57±3 kJmol^-1), suggesting that the deformation energy during loading in TeO₂-based glasses is largely increased due to nanocrystallization. The main origin of plastic deformation at h_t<600 nm is considered to be densification.