  Diamond single crystals showing Infra-red features of pressurized CO2-I phase
were studied using Transmission Electron Microscopy (TEM) and tomography.
Numerous O-containing precipitates with sizes up to 45 nm are observed. The
absolute majority of these precipitates decorate dislocation loops or are
located inside them; individual scattered precipitates are also present.
Morphology of the precipitates varies from quasi-isometric octahedra to highly
flattened elongated ones. Close association of the precipitates with the
dislocation loops implies their formation by exsolution of oxygen impurity from
diamond lattice; the size distribution of the precipitates suggests that the
equilibrium state is not yet reached. Presumably, the morphology and precise
chemical composition depend on P-T-t evolution of the diamond crystal and
corresponding changes in oxygen supersaturation in the lattice. The
CO2-containing diamonds often contain micron-sized hexagonal lamellar
inclusions. TEM investigation of a lamellae reveals that it consists of high
quality graphite showing partial epitaxial relation with comprising diamond.
The gap between the graphite and diamond may be enriched with oxygen impurity.
