The crystallite size of pyrolytic graphite

x-ray line broadening techniques have been used to determine both a- and c-direction crystallite sizes for a range of pyrolytic graphite samples whose effective formation temperature lay between 2330 and 3020°C. x-ray line profiles were analysed using the variance method. It is shown that if the proper allowance is made for the stacking fault contribution to the 110 line, the x-ray determination gives results for the a-direction crystallite size in good agreement with estimates obtained from the mobility and thermal conductivity of the samples. The a-direction crystallite sizes ranged from 0·01 to 3 μm and gave a thermal activation energy of 5·9 eV for a-direction crystallite growth. The crystallite size ratio L_a/L_c increased linearly with formation temperature in the range 2500 to 3020°C reaching a value of 36 at 3020°C.