Twins Diamond Crystals Grown at High Temperature and HighPressure from the Fe-Ni-C System

Twin diamond crystals grown at high temperature and high pressure (HPHT) in the presence of FeNi catalyst have been xamined by transmission electron microscopy (TEM). Direct observation by TEM shows that there are a large amount of twins which lie on the 111 planes in the HPHT-grown diamonds. The twins in the diamond may be formed and may extend into the inner crystal from the twin nucleus formed in the nucleation process. The twins can be formed due to the carbon atoms falling mistakingly into positions where a twin crystal can form during diamond growth, or condensation of supersaturated vacancies on the 111 plane. Some hexagonal dislocation loops related to supersaturated vacancies are found on the twins. The Moiré fringe image reveals that stacking faults terminate on intersecting twin boundary. This suggests that, at the temperature that the HPHT diamond is grown, the bordering partial has propagated by gliding up to the twin interface, which can be described by the reaction of a Shockley partial dislocation with a twin on the 111 plane.