Elastic Neutron Scattering Studies of H₂ and D₂ Physisorbed Stage 2 Graphite-Potassium

Abstract

The stage 2 MC₂₄ (M=K,Rb,Cs) compounds exhibit low temperature physisorption for a variety of gases (H₂,CH₄,N₂,etc.) [1]. Physisorption of gases such as these has also been observed in the Cs-intercalated layer-chalcogenide Cs-ZrS₂ [2]. A particularly striking feature of hydrogen physisorption occuring in the GIC systems is that hydrogen isotopes are physisorbed more readily than hydrogen itself [3,4,5]. In K-graphite, to accomodate the adsorbate species within K-intercalant layers, the interlayer separation between carbon bounding layers expands by ~.30Å. This is in contrast to stage 2 Rb- and and Cs-graphite where no expansion is observed due to the larger diameter of the Cs⁺ and Rb⁺ ions.