Long-term natural physical aging in glassy Ge5Se95 as probed by combined NMR and PAL spectroscopy

Structural rearrangements associated with long-term natural physical aging in glassy Ge5Se95 are studied using combined methods of solid state 77Se nuclear magnetic resonance and positron annihilation lifetime spectroscopy. Ab initio quantum chemical calculations with RHF/6-311G⁎ basis set was performed to justify the character of the observed destruction-polymerization transformations possible during long-term natural storage of Ge5Se95 glass. It is shown that some amount of directly corner-shared GeSe4/2 tetrahedrons present in as-prepared glasses slowly transform under prolonged physical aging in a more uniform glassy network composed by nearly-equal Se chains between neighboring GeSe4/2 tetrahedrons. These transformations are accompanied by atomic shrinkage with character fragmentation of free-volume voids typical for chalcogen-rich glasses. The observed effect in Ge5Se95 glass is compared with similar changes in long-term aged As-Se glasses having short (As30Se70) and long (As10Se90) selenium chains.