STABILITY AND CRYSTAL-STRUCTURE OF BC8 GERMANIUM

It is found that samples of crystalline germanium brought rapidly ( < 1 s) to ambient pressure from 14 GPa transform to the so-called BC8 st ructure rather than to the ST12 structure that is found on slower pres sure decrease. The BC8 phase is unstable at atmospheric pressure, but we have been able to record angle-dispersive powder patterns within le ss than 30 minutes of pressure release using an image-plate detector o n a synchrotron source. The refined crystal structure of BC8-Ge is ver y similar to that found previously for BC8-Si.