Equilibrium Values for High Pressure Transitions of Germanium and a New High Pressure Form of Germanium

摘要

Very long runs, by superpressure standards, of up to three weeks near 100 kbars have demonstrated the extreme sluggishness of some transitions in Ge and other semiconductor systems. This raises serious questions about the significance of the pressure values attached to various transitions and to the reality of some phase diagrams based on discontinuities observed in optical or electrical properties in an essentially dynamic system. The successful recovery of high pressure phases in semi-conductor systems by quenching to and working at 'dry ice' temperatures has been demonstrated. In the system Ge, a new high pressure polymorph, Ge-IV, has been synthesized above 110 kbars with a bcc structure analogous to Si. The equilibrium transformation pressure for the reaction Ge-I reversibly yields Ge-III(bct) has been revised downward from about 120 kbars to 40 kbars at 30C. The transition from the Ge-I diamond structure to the Ge-II white tin structure is always metastable. (Author)