A new compound was identified, in the Al2O3-A4C3-AlN system, which crystallized in a diamond-related structure. The compound had a rhombohedral structure (R3m) with a = 0.5891nm and  = 55.15. The compound had a very limited phase width with respect to the molar C/O ratio and the Al content. The electron diffraction results were in agreement with the structure which was determined by means of X-ray powder diffraction. High-resolution transmission electron microscopy revealed the existence of twin defects in the (100) plane (hexagonal description).

W.A.Groen, M.J.Kraan, P.F.Van Hal, A.E.M.De Veirman: Journal of Solid State Chemistry, 1995, 120[2], 211-5