A study of the amplitude of vibration of carbon atoms in the graphite structure

Abstract

The changes with temperature in the integrated intensity of the 0004 and 0006 reflections from graphite specimens have been measured by means of an X-ray counter diffractometer, using a high temperature attachment developed originally for thermal expansion studies. Three varieties of graphite were examined, a spectroscopic material p≅0·2, a pyrolytic carbon of p≅0·1 and a pyrolytic carbon p≅0·8. The range of temperature between 1200 and 2500°C was covered. Values of the amplitude of vibration of carbon atoms normal to the layer planes were derived from the intensity measurements and a room temperature value of 0·099 Å was assumed. Tables and graphical representations of the results are presented. It is shown that the amplitude of vibration increases continuously with temperature for all the samples in the temperature range considered and at elevated temperatures the amplitude increases nearly as rapidly as the interlayer spacing; hence the mean “free space” between the layer planes decreases as temperature increases. The degree to which atomic movement is hindered in the graphite structure is a function of stacking disorder and not of the degree of preferred orientation of the graphite.