KNbGeO 5 (i.e., 25K2O-25Nb2O5-50GeO2) glass with the glass transition 622 °C and crystallization onset 668 °C temperatures shows prominent nanocrystallization, giving K3.8Nb5Ge3O20.4 nanocrystals with the size of ∼30 nm. Dielectric, elastic and mechanical properties of transparent nanocrystallized KNbGeO5 glasses are examined using some techniques such as polarizability analysis, cube resonance spectra and Vickers nanoindentation. Electronic polarizability, shear modulus, bulk modulus, Young’s modulus (E), Debye temperature (θD), Vickers hardness, and deformation energies during nanoindentation increase largely due to the nanocrystallization, e.g., E=64.1 GPa and θD=500 K for the base glass and E=85.5 GPa and θD=575 K for a transparent nanocrystallized glass. The values of Poisson’s ratio and fractal bond connectivity of nanocrystallized glasses are the same as those of the base glass, suggesting that relative arrangements of constituent ions (K+, Nb5+, Ge4+) in nanocrystallized glasses are basically similar to those in the base glass. The present study suggests that nanocrystallization in glass results in not only more compact atomic arrangements but also in an increase in interatomic strength.
Transparent surface crystallized glasses consisting of c-axis oriented nonlinear optical Ba2TiGe2O8 crystalline layers (~10 μm)at the surface of 40BaO·20TiO2·40GeO2 glass are prepared, and their deformation behaviors are examined from the load/ unload displacement curves obtained with the Vickers nanoindentation technique. It is found that the surface crystalline layers deform easily in small loadings during Vickers nanoindentations in comparison with the precursor glass with a homogeneous random glass structure. The surface crystalline layers subjected to the penetration depth of h = 0.5 μm show a large elastic recovery of ~70% compared with that (49%) in the precursor glass. The sliding (displacement) of about 0.02 μm is observed immediately after the stop of the loading with a loading speed of 5 μm/s in the surface crystallized samples. The present study suggests that the deformation behaviors of the surface Ba2TiGe2O8 crystalline layers in the crystallized glass might be closely related to the assemblage state of highly oriented crystals, in particular, the bonding (i.e., the degree of the adhesion ) among c-axis oriented crystals might be weak.
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