Hall effect in potassium-hydrogen-graphite intercalation compounds and their conduction mechanism.

Abstract

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 ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ 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 ${\mathit{R}}_{\mathit{H}}$ and conductivity tensor ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{y}}$ 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 \ensuremath{\pi} electrons. The scattering mechanism for the ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ 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 ${\mathrm{K}}^{+}$${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ intercalate layers below 80 K, in addition to a low-energy optical-phonon scattering, which is operative mainly at higher temperatures.