Abstract
Studies of the x-ray diffraction pattern from different potassium graphites have shown that intercalation of graphite by potassium is accompanied by an expansion of the carbon layers. This expansion is uniform within a single layer and is constant for all n carbon layers separating successive intercalate layers in the stagen compound of composition C12nK (n > 1). Preferred values of the C-C bond length for stages 1 to 6, derived from the value of the a-axis parameter extrapolated to θ = 90° are:
| Stage 1 | 1·43204 (3) Å |
| 2 | 1·42592 (3) |
| 3 | 1·4240 (1) |
| Stage 4 | 1·42305 (7) Å |
| 5 | 1·42267 (6) |
| 6 | 1·4221 (1). |
Lower accuracy in stages 3 and 6 is due to slight variation between samples, attributed to deviations from the ideal stoichiometry. Before intercalation, the C-C bond length of the pyrolytic graphite was 1·42114 (3) Å.
The bond-length expansion is consistent with electron transfer from potassium to the antibonding orbitals in the upper π band of the graphitic region between successive intercalate layers. The discontinuous change of bond length with stage can be approximately represented by the relation: C-C (stagen) = (1·4203+0·0113/n)Å.