Super cold-crystallization of sodium iodine in selenium based chalco-halide glasses

Mechanical properties of a chalco-halide glass of the composition (0.72 GeSe2–0.28 Ga2Se3)75 NaI25 are studied during isothermal treatment below Tg (Tg-60 °C). The evolution of the Young's Modulus (E), the damping (Q−1) and the apparent viscosity (J−1, reverse of the creep rate) during heat treatment show that a structural rearrangement occurs in the glass below Tg. X-Ray diffraction and transmission measurements of the sample after heat treatment highlight the beginning of a super cold crystallization of cubic NaI within the glass after 1 month at Tg-60 °C. After 3 months of heat treatment, NaI crystals of about 31 nm size have been observed in the glass matrix by transmission electron microscopy.