Hexagonal starting material was mechanically milled in order to introduce lattice defects, before its conversion to the cubic phase. The synthesis of the latter was then greatly facilitated due to a mechanochemical effect. Under 7.7GPa, the formation of the cubic phase began at 1250C in pre-milled powders, and at 1450C in non-milled powders. High-resolution transmission electron microscopy confirmed that various defects formed in the hexagonal phase during milling. The hexagonal phase changed to wurtzite-type material upon compression in the c-direction, and a slight tilt in the interface between (00•2)hexagonal and (00•2)wurtzite partially compensated for the lattice misfit between the basal planes of both phases. Characteristic stacking faults appeared in the hexagonal phase upon heating under high pressures. They were replaced by the formation of wurtzite-type material during compression and were nucleation sites for the cubic phase.

Facilitated Synthesis of Cubic Boron Nitride by a Mechanochemical Effect. S.Horiuchi, J.Y.Huang, L.L.He, J.F.Mao, T.Taniguchi: Philosophical Magazine A, 1998, 78[5], 1065-72