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Diamond crystals, with dimensions of about 0.5-0.6 mm, were synthesized in the presence of Fe-Ni and Fe-Ni-Si catalyst solvents under high-pressure-high-temperature (HPHT) conditions. The as-known dendritic pattern was clearly seen on the (111) or (100) planes of diamond single crystals grown using Fe-Ni as a catalyst solvent. However, the conventional dendritic pattern was not observed in diamonds grown in the presence of Fe-Ni-Si alloy catalyst. Trigonal-type, pyramid-type, polygonal-type and rectangular-type growth hillocks were clearly observed on the (111) and (100) surfaces of diamonds grown from the Fe-Ni-Si-C system, and the density of the hillocks is very high at some positions. Clear successive growth layers can also be found on the (111) planes of the high-pressure diamond single crystals grown in the presence of Fe-Ni-Si alloy catalyst. The growth hillocks distributed on the (111) and (100) planes of the diamonds generally occur on or near growth steps, and some of the hillocks terminate at certain solid inclusions and voids. Growth hillocks on the (111) and (100) surfaces directly indicate the spiral growth mechanism under HPHT. A possible formation process for growth hillocks is proposed.

Twin diamond crystals grown at high temperature and high pressure (HPHT) in the presence of FeNi catalyst have been examined 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 mistakenly 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 Moire fringe image reveals that stacking faults terminate on the 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.

Diamond growth instability at high temperature and high pressure (HPHT) has been elucidated by observing the cellular interface in diamond crystals. The HPHT diamond crystals grow layer by layer from solution of carbon in the molten catalyst. In the growth of any other crystals from solution, the growth interface is not stable and should be of the greatest significance to understand further the diamond growth mechanism. During the diamond growth, the carbon atoms are delivered to the growing diamond crystal by diffusion through a diamond crystal-solution boundary layer. In front of the boundary layer, there is a narrow constitutional supercooling zone related to the solubility difference between diamond and graphite in the molten catalyst. The diamond growth stability is broken, and the flat or planar growth interface transforms into a cellular interface due to the light supercooling. The phenomenon of solute trails in the diamonds was observed, the formation of solute trails was closely associated with the cellular interface.

Nucleation and growth of diamond in the catalyst alloy Ni70Mn25Co5, wt% have been observed at high temperature and pressure.

The morphology of recrystallized graphite in the presence of catalytic elements has been studied and it revealed a relationship between recrystallized graphite and diamond growth.