Mechanical and elastic properties of transparent nanocrystalline TeO2-based glass-ceramics

Mechanical and elastic properties of transparent TeO2-based glass-ceramics (15K2O · 15Nb2O5 · 70TeO2) consisting of nanocrystalline particles (each particle size: 40–50 nm) and showing optical second harmonic generation were evaluated by means of usual Vickers indentation and nanoindentation tests. The precursor glass has Vickers hardness H v of 2.9 GPa, Young's modulus E of 54.7 GPa, the fracture toughness K c of 0.25 MPam1/2 and Poisson's ratio of 0.24. The transparent nanocrystalline glass-ceramic heat-treated at 420°C for 1 h has H v = 3.8 GPa, E = 75.9 GPa and K c = 0.34 MPam1/2, and the opaque glass-ceramic heat-treated at 475°C for 1 h has H v = 4.5 GPa, E = 82.9 GPa and K c = 0.68 MPam1/2, demonstrating that poor mechanical and elastic properties of the precursor TeO2-based glass are improved through sufficient crystallization. The fracture surface energy, brittleness and elastic recoveries (about 44%) after unloading (the maximum load: 30 mN) of transparent nanocrystalline glass-ceramics are almost the same as those of the precursor glass, implying that the interaction among nanocrystalline particles is not so strong.