Synchrotron X-ray diffraction observation of phase transformation during annealing of Si processed by high-pressure torsion

In situ observation of a phase transformation during annealing of Si containing diamond-cubic (dc) and metastable phases has been performed using synchrotron X-ray diffraction. Metastable body-centred-cubic (bc8) and rhombohedral (r8) phases were formed by high-pressure torsion. These metastable phases gradually disappeared when increasing the annealing temperature to ∼ 180°C while another metastable phase having a hexagonal diamond (hd) structure appeared at ∼ 190°C. High-resolution transmission microscopy analysis revealed that hd and dc grains were present after annealing at 200°C. The results indicate that a phase transformation, mainly from bc8 to hd, occurred during annealing.