  In pyrocarbon materials, the width of the Raman D band (FWHMD) is very
sensitive to low energy structural defects (e.g., disorientations of the
graphene layers). The correlation between the two parameters, FWHMD and OA (as
derived from selected area electron diffraction: SAED), has allowed to
differentiate various pyrocarbons unambiguously. Furthermore, the optical
properties of pyrocarbons, i.e., the extinction angle, the optical phase shift
and the ordinary and extraordinary reflectance, have been accurately determined
at 550 nm by means of the extinction curves method. These results are completed
by in-plane and out-of-plane dielectric constant measurements by angular
resolved EELS. Moreover, the hybridization degree of the carbon atoms has been
assessed by the same technique. About 80% of the carbon atoms of the
pyrocarbons have a sp2 hybridization. The lack of pure sp2 carbon atoms, as
compared to graphite, might be explained by the presence of sp3-like line
defects.
