Structure, elastic properties and strength of amorphous and nanocomposite carbon

We study theoretically the equilibrium structure, as well as the response under external load, of characteristic carbon-based materials. The materials considered include diamond, amorphous carbon (a-C), ``amorphous diamond'' and nanocomposite amorphous carbon (na-C). A universal bulk-modulus versus density curve is obeyed by all structures we consider. We calculate the dependence of elastic constants on the density. The strength of a-C was found to increase in roughly a linear manner, with increasing concentration of four-fold atoms, with the maximum stress of the strongest a-C sample being about half that of diamond. The response of na-C to external load is essentially identical to the response of the embedding a-C matrix.