黒鉛-ハロゲン残存化合物の電流磁気効果

抄録

By means of a precision dc-amplification technique, the halogen-dope effect on galvanomagnetic properties of a reactor-grade polycrystalline graphite has been investigated at liquid nitorogen temperature in the range of magnetic field intensity up to 10 kG. Br₂ and IC1 were chosen as dopants respectively.
When the halogen concentration was order of 10^-2 at. % or less, the transport properties were little affected by the presence of such impurities. This may imply that most parts of impurities precipitate probably to inter-crystallite boundaries in the form of clusters. As the concentration increases beyond 10^-1 at. %, the Hall coefficient changes its sign and the resistivity as well as the magnetoresistance tends to decrease by a factor of more than two; which means that halogens flood into the crystallites so as to change the electronic structure. In the X-ray diffraction study examined at the same time, it has been observed that the d (004)- spacing is subjected to little change but the crystallite size La to considerable decrease. Qualitative discussions are given of the data in terms the simple two-band scheme, which has led to a conclusion that the ionization efficiency of these halogen impurities is pretty low.