EXAFS study of amorphous selenium under pressure

Extended X-ray absorption fine structures (EXAFS) of amorphous solids selenium (a-Se) under pressures from 0 to 10 GPa and liquid Se at 10 GPa were studied. Structure of a-Se changed gradually with pressure until crystallization was induced at 10 GPa. In spite of the compression, the covalent bond length of a-Se increased slightly with pressure and rapidly just before the crystallization. The correlation between interchain atoms in a-Se was much weaker than that in crystalline Se at low pressures. It became prominent under higher pressure before the crystallization. EXAFS spectrum of liquid selenium at 10 GPa was successfully measured. The weakening of covalent bond upon melting under high pressure was observed.