Structure and synthesis of the ternary alkali graphite intercalation compound KCsC16, an ideal layered heterostructure

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Abstract
We have prepared a stable two phase graphite intercalation compound (GIC) containing KC8 and KCsC16 by immersing CsC24 into liquid K at 70 °C. High resolution x‐ray diffraction studies reveal that the KCsC16, which exhibits a stage one c‐axis stacking sequence of ⋅⋅⋅ C K C Cs C K C Cs ⋅⋅⋅ is an ideal ternary heterostructure GIC with a c‐axis repeat distance of dH=11.27 Å and correlation range of 350 Å. The intensities of the (00l) x‐ray diffraction pattern calculated on the basis of the proposed c‐axis repeat sequence are in excellent agreement with the experimental observations. The KCsC16 in plane structure is a (2×2)R0 ° superlattice with an in plane correlation range of 140 Å. The ordered intercalant layers stack along the c axis with an α,β,γ,δ site sequence, where, e.g., α,γ=K and β,δ=Cs, and stacking faults occur on average every 30 Å.