Pressure-induced crystallization and metallization in glassy As20Se80

As20Se80 glass (g-As20Se80) was studied under static high pressure using in situ Raman spectroscopy, x-ray diffraction, and electrical measurements. With increasing pressure, g-As20Se80 shows a breakdown of intermediate-range ordering around 6 GPa and then becomes metallic above 9 GPa. It subsequently undergoes a pressure-induced crystallization, towards the β-Po-type crystal structure (c-AsSe4 phase), above 20 GPa. Crystalline c-AsSe4 remains in this structure up to at least 35 GPa. This structure is identical with the one observed for pure c-Se, albeit at much higher pressures. The pressure-induced metallization and crystallization are fully reversible upon pressure release, with considerable hysteresis. The results are discussed in comparison with the general structural phase diagram of c-Se under pressure and the implication of pressure-induced crystallization towards understanding the nature of the glass transition.