Structural evolution mechanisms of amorphous and liquid As2Se3 at high pressures

The elusive structure of compressed, melt-quenched As 2 Se 3 was studied in both its liquid and amorphous form up to 4.4 and 30 GPa, respectively, by means of x-ray absorption spectroscopy and diffraction. The evolution of the short-range structure is studied by As and Se multiple K-edge extended x-ray absorption fine structure (EXAFS) refinement, while changes in intermediate-range ordering are revealed by x-ray diffraction and near-edge structures. In the liquid, at the nearest-neighbor length scales, a gradual disordering and slight elongation of the As-Se average distances is observed, preserving the local coordination upon increasing pressure, whereas substantial compression and disordering are observed at intermediate distances. Similarly, in the amorphous form we found a progressive slight elongation and disordering of the first-neighbor As-Se average distance R (from ̊ 2 ) upon increasing pressures up to 30 GPa. ̊ and bond variance σ 2 (from ∼0.004 to 0.008 A ∼2.42 to 2.44 A) On the other hand, gradual shortening of the second and farther neighbor distances, more evident below 15 GPa, are compatible with data analysis. No sign of crystallization and gradual metallization are observed for amorphous a-As 2 Se 3 up to 30 GPa. The emerging picture for the structure evolution under high pressures is a compaction mechanism involving mainly changes at intermediate distances, weakly affecting the first-neighbor bonding character.