Dislocations and plasticity of experimentally deformed coesite

Dislocation microstructures have been characterized by transmission electron microscopy in polycrystalline coesite deformed experimentally at 4 GPa, 1200°C. Burgers vectors have been determined by large-angle convergent-beam electron diffraction. Sample orientation was assisted by precession electron diffraction to overcome difficulties arising from pseudohexagonal symmetry. The results are explained by using a pseudo-hexagonal setting. We found that most dislocations observed are of the 1/3 <2110> type. No clear glide plane was identified, suggesting that climb is activated under these conditions. This conclusion is supported by the observation of numerous subgrain boundaries. We have also observed some [0001] dislocations. Finally, the C12/c1 space group to which coesite belongs being centred, an additional slip system is observed: 1/6[1213](0111) (1/2[110](110) in the monoclinic setting).