Structure and dynamics of microcrystalline graphite, graphon, by neutron scattering

Abstract

The structure and dynamics of “graphon”, a carbon black, have been characterised by a combination of neutron diffraction and inelastic scattering experiments. The techniques employed were those of neutron diffraction, time-of-flight and beryllium-filter spectroscopy.

The dimensions of the unit cell were found to be: a= 2.47 ±(0.01)Å, c= 6.93 ±(0.01)Å, and the average dimensions of the layer lattice were estimated from high angle diffraction as L_a= 30 Å and L_c= 85 Å.

Well-defined average phonon groups were observed by inelastic scattering and used to construct an almost sinusoidal dispersion curve for longitudinal acoustic lattice vibrations along the c-axis. The stiffness constant C₃₃, found from the dispersion curve, was 3.00 ±(0.02)× 10¹¹ dyn cm^–2. The frequency distribution of the lattice vibrations shows singularities at energies qualitatively in agreement with those calculated by Young and Koppel from specific heat measurements on graphite.