Influence of temperature and point defects on the X-ray diffraction pattern of graphite

The atomic structure of pure and defective graphite has been modelled using classical many body potentials from which simulated powder X-ray Diffraction (XRD) patterns were produced using the Debyer software. The changes in the XRD patterns due to both heating and the inclusion of defects were investigated. After heating, the results show a shift in the 004 Laue peak in qualitative agreement with experiment. The c parameter is shown to increase over the temperature range 0 – 1000 K but there is a slight reduction in the a parameter over this range. The scattering angle for the 004 peak reduces with the introduction of defects up to ≈ 5% defect concentration for both vacancies and interstitials with a larger reduction in the case of interstitials. The intensity of the scattering peak is reduced with increasing interstitials (25% reduction at 5% concentration), but remains relatively constant with increasing vacancies. The introduction of a small percentage of interstitials causes an increase in both the a and c parameters but vacancies cause a reduction in the a parameter.