Characterisation of Si III and Si IV, metastable forms of silicon at ambient pressure

Two crystalline phases of silicon: Si III (BCC) and Si IV (hexagonal diamond) are known to be metastable at ambient. Pure, single phase, microcrystalline samples of both varieties may be prepared by high-pressure synthesis above 18 GPa at 300 K. The authors report on high-resolution electron microscopy, kinetics of the temperature driven phase-change from Si III to Si IV, and Raman scattering measurements performed on these samples. Results are compared with those obtained by other characterisation methods and/or published in earlier works.