HALL-EFFECT IN POTASSIUM-HYDROGEN-GRAPHITE INTERCALATION COMPOUNDS AND THEIR CONDUCTION MECHANISM

The Hall effect and magnetoresistance were measured for stage-1 and -2 potassium-hydrogen-graphite ternary intercalation compounds (KH-GIC's) in the temperature range 1.4-250 K, in order to investigate their electronic structure and transport properties. The presence of two kinds of carriers was found: majority carriers in the graphitic pi* bands with electron character and minority hole carriers in the free-electron-like hydrogen 1s band. The hole carriers in the H 1s band are associated with the incomplete charge transfer to the hydrogen species. The Hall coefficient R(H) and conductivity tensor sigma(xy) component exhibit large temperature dependences, which are considered to be due to the different in-plane scattering mechanisms for the two kinds of carriers. The hole carriers were found to have high mobilities, comparable to the mobilities of the graphitic ir electrons. The scattering mechanism for the pi* bands can be explained in terms of an acoustic-phonon scattering process with small effective masses and a large deformation potential. On the other hand, that for the H 1s band is dominated by an acoustic-phonon scattering process, with a small deformation potential in the ionic K+H- intercalate layers below 80 K, in addition to a low-energy optical-phonon scattering, which is operative mainly at higher temperatures.