Pressure-induced crystallization and phase transformation of amorphous selenium: Ramanspectroscopy and x-ray diffraction studies

Abstract

High-pressure Raman spectroscopy studies have been carried out on amorphous Se (a-Se)at room temperature in a diamond anvil cell with an 830 nm exciting line. Raman evidencefor the pressure-induced crystallization of a-Se and the coexistence of the unknownhigh-pressure phase with the hexagonal phase is presented for the first time. Furtherexperimental proof of high-pressure angle-dispersive x-ray diffraction studies for a-Seindicates that the unknown high-pressure phase is also a mixture phase of the tetragonalI41/acd and Se IV structure. Our Raman and x-ray diffraction results suggest that hexagonal Se Iundergoes a direct transition to triclinic Se III at about 19 GPa, which is in good agreementwith the theoretical prediction.