Low Temperature Electron-Irradiation Damage and Recovery in Pyrolytic Graphite

The electrical resistivity changes by electron irradiation at 5 K and the isochronal annealing of resistivities in the temperature range 5-85 K (Stage I) in pyrolytic graphite are studied in order to get information on point defects. Both the a -axis and the c -axis resistivity changes by irradiation are explained by the ordinary transport theory with defect scattering. Small recoveries in Stage I are shown to be composed of four substages: I A (5-15 K); I B (15-45 K); I C (45-65 K); and I D (65-85 K). Effects of the irradiating electron energy, the radiation-doping and the graphitization temperature of samples on these substages are also studied. Substages I A and I B may be caused by the correlated rearrangement of close Frenkel pairs, where interstitial atoms form loose coupling with their own vacancies. The activation energy for I A is roughly estimated to be 0.027±0.004 eV. In I C the long-range free migration of interstitial atoms seems to occur.