Hardness, toughness, and scratchability of germanium-selenium chalcogenide glasses
Résumé
Ge-Se chalcogenide glasses are characterized by relatively low hardness (0.39-2.35 GPa) and low fracture toughness (0.1-0.28 MPa.m(1/2)). Actually, the hardness of chalcogen-rich glasses is low enough so that the brittleness parameter, B = H/K-c, is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge20Se80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness.