AMORPHIZATION FROM THE QUENCHED HIGH-PRESSURE PHASE OF SILICON AND GERMANIUM

The phase transitions from the quenched high-pressure phase, including amorphous state, have been investigated for crystalline silicon and germanium at various pressures. X-ray diffraction patterns have been measured at pressures up to 15 GPa and temperatures down to 90 K by an energy-dispersive method using synchrotron radiation and a diamond anvil cell. The quenched beta-Sn phase undergoes an amorphous phase transition when heated at 1.5 GPa for c-Si and 2.0 GPa for c-Ge. On the other hand, the quenched beta-Sn phase transforms into a metastable crystalline phase when heated at higher pressures. The phase behavior is discussed in relation to the pressure dependence of the height of potential barrier between the beta-Sn and amorphous phases and that between the beta-Sn and metastable crystalline phases. The coordination number for the pressure-induced amorphous germanium, obtained through amorphization, from the quenched high-pressure phase, is estimated to be about 4.