Morphology of diamond crystals grown in magnesium-based systems at high temperatures and high pressures

• We studied the growth of diamond crystals on seeds in magnesium-based systems.
• Inhibition of the growth of the {100} faces occurs when the Mg content is 45–50 at%
• Plane-faceted crystals are transformed into antiskeletal forms.
• Diamond growth inhibition is associated with supply of oxygen from materials of the cell.

A series of experiments on diamond growth in the Mg45Cu55–C, Mg50Ni50–C, Mg50Cu25Ni25–C, Mg50Ag25Ni25–C and Mg25Cu25Ni50–C systems at a pressure of 6.3 GPa in the temperature range of 1550–1650 °C was conducted. The morphology of diamond crystals and the features of their growth were studied. The {111} and {100} faces, with the cube faces playing the dominant role, were found to be the plane-faced forms of diamond crystal growth. If the magnesium content in the system is 45−50 at%, crystal growth occurs in the regime of inhibition of the {100} faces with the formation of antiskeletal crystals. In case of a constant intensity of the face inhibition up to its complete growing out, the quasi-faces of trapezohedron {311} are formed with striations in the [110] direction. The inhibition of face growth and formation of antiskeletal crystals are related to oxygen inflow from the cell parts and are accompanied by crystallization of magnesium oxide on the diamond surface. A reduction in the magnesium content in the system from 50 to 25 at% or an increase in the temperature leads to the cessation of {100} face inhibition and promotes growth of plane-faced crystals.