Final Activity and Management Report Summary - POLYAMORPHIC SYSTEMS (High-pressure phase transitions inpolyamorphic systems of semiconducting elements) The effect of pressure on amorphous Ge was probed by Raman spectroscopy combined with molecular dynamics simulations. A large jump occurs in Raman peak position at 11-12 GPa and 7-5.5 GPa respectively during increasing/decreasing pressure runs. This effect is due to a transition between the Low density amorphous semiconductor (LDA) and a metallic high density (HDA) modifications of amorphous germanium. We measured the superconducting transition temperature (Tc) using magnetic susceptibility measurements in the diamond anvil cell. The Tc for the HDA modification was found substantially higher than that for the beta-Sn structured Ge-II crystalline phase.Our results demonstrate that HDA form of Ge contains atoms in higher average coordination than the tetrahedrally-bonded LDA polyamorph. During compression the LDA-to-HDA transformation occurs at P app. 8-12 GPa, while a reverse transformation occurs between P app. 5.5-6.5 GPa indicating hysteresis characteristic for the first order-like transition as observed previously for a-Si at slightly higher pressure. We expect that the LDA-HDA transformation in amorphous Ge is linked to a density-driven liquid-to-liquid phase transition that is predicted theoretically to occur in the supercooled liquid state of Ge.
