Europhys. Lett, 44 (2), pp. 255-260 (1998)
Measurement of anisotropies of the kinetic energy and
pyrolytic graphite by neutron
A. L. Fielding 1, D. N. Timms 1 and J. Mayers 2
1 Division of Physics, Portsmouth University, St. Michael's Building
Portsmouth PO1 2DT, UK
2 ISIS Facility, Rutherford Appleton Laboratory
Chilton, Didcot, OX11 0QX, UK
(received 2 February 1998; accepted in final form 31 August 1998)
PACS. 81.05 - Specific materials: fabrication,
treatment, testing and analysis.
PACS. 32.80Cy - Atomic scattering, cross sections, and form factors; Compton scattering.
PACS. 78.70Nx - Neutron inelastic scattering.
Neutron Compton scattering (NCS) measurements of the anisotropy of the momentum distribution and the mean Laplacian of the interatomic potential have been performed using electron volt neutrons, with wave vector transfers between and . The measured momentum distribution of the atoms displays significantly more anisotropy than a calculation using a model density of states. We have observed anisotropies in for the first time. The results suggest that the atomic potential is harmonic within the graphite planes, but anharmonic for vibrations perpendicular to the planes.