Structure of intermediate carbon phase formed under shock compression of ultradispersed graphite materials

Abstract

We have studied the structure of the products of high-temperature shock compression of wood charcoal by x-ray diffractometry and transmission electron microscopy. We have shown that as a result of phase transformations at high pressures (30 GPa) and temperatures (above 2500 K), besides nanocrystalline diamond we see formation of an amorphous carbon phase having a density intermediate between the densities of the original charcoal and diamond. Based on comparison of the observed diffraction patterns with the patterns calculated for different models for amorphous carbon, and also considering the intermediate value of the density for the amorphous phase, we have concluded that this phase has the short-range order of the hypothetical H-6 structure, characterized by a three-dimensional framework of sp2 bonds. The amorphism of the intermediate phase is due to both the crystallographic nature of the H-6 structure and the disorder of the original structures, the regular rearrangement of which to form crystalline structures is not possible.