Impurity-Dope Effects on the Anelasticity of Graphite

Abstract

By means of a resonant bar technique, the impurity-dope effects on the anelastic properties of various graphites have been investigated at temperatures ranging from 290°K down to 4.2°K. A pronounced peak in the internal friction vs. temperature diagram for polycrystalline graphite has been found to grow up, with stepwise bromination up to 0.25% Br/C, and to shift toward higher temperature side from the original position around 50°K. Also for the pyrolytic graphite boronated to 0.5 at. % a similar relaxation peak was found around 80°K. As to the background component, an analysis in the framework of the Granato-Lücke theory was examined on the resonant frequency vs. temperature relationship, and has yielded the activation energy values for thermal depinning of dislocations as follows; 0.04 eV and 0.03 eV before and after the bromination respectively, and 0.006 eV for the boronateds. An interpretation of these observations is given, based on the duplex role of impurities in graphite, viz. pinning function and viscous drag effect to dislocations.