<p>This study examines the long-term devitrification of selenium over 25 years, examining structural, thermal, electrical, and mechanical changes. XRD analysis reveals an increase in crystallinity, accompanied by an apparent reduction in coherent diffraction domain size (CDDS) from 83.1 ± 4.1 nm in the fresh sample to 30.1 ± 1.5 nm after 25 years of ageing, accompanied by an increase in microstrain and dislocation density. The surface texture reveals surface roughening, microvoids, and cracks, indicating degradation. A narrowed glass transition and dual crystallization peaks suggest phase separation; the crystallization activation energy increases with ageing. The augmentation in ε‘ to 29.8 and ε“ to 14.04 in aged samples is due to dipolar and space charge polarization. Microhardness decreases from 84.6 to 45.6 kgfmm⁻², accompanied by an increase in microvoid volume and a reduction in modulus and yield strength. Hence, the slow devitrification as a sign of physical ageing in selenium glasses leads to structural relaxation, increased crystallinity, and compaction at the atomic scale, resulting in improved thermal and electrical behavior but compromised mechanical resilience. These insights are crucial for predicting the long-term performance and stability of chalcogenide glasses in technological applications.</p>