Shubnikov-de Haas experiments on potassium-hydrogen graphite intercalation compounds (KHx-GIC's).

Abstract

Potassium-hydrogen-graphite ternary compounds (${\mathrm{KH}}_{\mathrm{x}}$-GIC, 0x1) are donor-type compounds containing an ionic intercalant ${\mathrm{K}}^{+}$${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$. Basically the effect of hydrogen addition is the uptake of electrons from the potassium so that fewer electrons are available for conduction in the graphite \ensuremath{\pi} bands. To obtain Fermi-surface information directly, Shubnikov--de Haas (SdH) measurements were carried out on stage-1, -2, and -4 ${\mathrm{KH}}_{\mathrm{x}}$-GIC's. The results are compared with the electronic properties of K-GIC's and ${\mathrm{KHg}}_{\mathrm{x}}$-GIC's. The observed oscillations are qualitatively modeled using the three-dimensional dilute-limit model. These Fermi-surface results are related to other experiments on ${\mathrm{KH}}_{\mathrm{x}}$-GIC's, such as magnetic susceptibility, electronic specific heat, Raman scattering, and superconductivity. For example, it is found that because of the strong electron affinity of hydrogen, the charge transfer to hydrogen and graphite in stage-2 ${\mathrm{KH}}_{\mathrm{x}}$-GIC's completely depletes the electrons in the potassium conduction band, consistent with the experimental specific-heat results. The basic conclusion that the uptake of hydrogen results in a lower electron concentration in the graphite \ensuremath{\pi} bands is supported by all experiments.