Graphite Intercalated with Potassium and Ammonia—A Metal-Ammonia Solution in Two Dimensions

Abstract

Several decades ago Rudöff and his coworkers [1] showed that graphite could be readily intercalated by metal-ammonia solutions (M-NH₃ where M = alkali metals, rare earth metals, etc.) if the host material was directly immersed into the deep blue liquid. Recently, we have shown using highly-oriented pyrolytic graphite (HOPG) host material that distinctly different M-NH₃ graphite intercalation compounds (GIC’s) are obtained when for instance an alkali binary GIC such as KC₂₄ is exposed to NH₃ vapor [2]. In the limited space of this brief report we will discuss the novel features of the room temperature absorption isotherm of K(NH₃)_xC₂₄, and its implications for the two-dimensional character of the K-NH₃ layer in the GIC. We will also present in-plane diffuse x-ray scattering results of the saturated (at P_{NH 3} ≅ 10 atm) compound K(NH₃)_4.33C₂₄. These results also support the 2-D nature of the intercalated metal-ammonia solution.