Lonsdaleite formation in process of reverse phase transition diamond–graphite

Synthetic diamond powder of micron size was annealed in an argon atmosphere at 1900 K during 15 min. An incomplete phase transition diamond → graphite was studied by the TEM (transmission electron microscopy) methods. Disruption of (111) diamond planes packing and the lonsdaleite layers formation took place in the process of annealing. Particles contained fragments of graphite, diamond and layers with defect structure. Among the fringes with the interplanar spacing d111 = 0.206 nm, corresponding to {111} diamond planes, some areas with the doubled interplanar distances 2 d111 were found, which were formed as a result of some sp3 -bonds rupture during the heating.

► Synthetic diamond powder of micron size was annealed in an argon atmosphere at 1900K during 15 minutes. ► Ellipsoids, onions, and similar structures were found on the (011) diamond plane. ► Layers with doubled interplanar distance in the diamond have been observed. ► Reflections with streaks in the diffraction pattern indicate the formation of lonsdaleite in diamond.