Table 1: Synthesis conditions and experimental results.

(GPa) (°C) (min)PhasesOptical appearance

15230020C-dia, H-dia*Transparent
15180020Gr, H-dia, C-diaOpaque
15130020Gr, H-dia, C-diaOpaque
15100020Gr, H-dia, C-diaOpaque

Gr: graphite, H-dia: Hexagonal diamond, C-dia: cubic diamond, *: trace amount.