Radiation-induced changes in some physical properties of graphites of various degrees of graphitization

Abstract

The absolute radiation-induced changes in electrical and thermal resistivities are, within the accuracy of the measurements, independent of the degree of graphitization. The relative changes in electrical resistivity and thermal conductivity are smaller for the less graphitized samples. The relationship between thermal conductivity and temperature indicates that the radiation-induced breakdown of the crystal lattice in graphite has the same effect on the propagation of thermal vibrations as the crystallite boundaries or impurities. The mechanism by which radiation affects the electrical conductivity of graphite appears to be that of forming additional traps for the current carriers. This suggestion is confirmed by the radiation-induced changes in the Hall coefficient which were observed previously. Swelling was practically absent in the experiments, which suggests that this phenomenon is due to less stable forms of radiation damage. It must be pointed out that if graphite is irradiated at room temperature, the swelling effect is quite stable, and is only removed by annealing at temperatures of at least approximately 2000 deg C. This suggests that radiation annealing occurred during the experiments. in virtue of the fact that certain crystal lattice defects are considerably less stable under the simultaneous action of heat and radiation than under themore » action of heat alone. (auth)« less