Structural study and crystal chemistry of the first stage calcium graphite intercalation compound

A novel and efficient synthesis method concerning the preparation of the first stage calcium graphite intercalation compound is provided. It makes use of a reaction between liquid metallic alloy and pyrolytic graphite. From now on it is especially easy to obtain bulk CaC6 samples. Thanks to such samples, it was possible to study in detail the crystal structure of this binary intercalation compound. It has been entirely specified, so that we know that CaC6 crystal is rhombohedral and belongs to the image space group with the following parameters: image and image. The elemental unit cell contains one calcium atom and six carbon atoms. In this paper, we show also how the various MC6 structures evolve according to the size of the intercalated element and to the bond nature that appears in the final compound. CaC6 is unique, since all the other MC6 compounds exhibit a hexagonal symmetry.