On the intercalation of potassium sulfide into graphite: synthesis, structure and relation with the structure of the free sulfide.

A first stage purple graphite intercalation compound has been successfully synthesized, by heating at 400 degrees C for 3 days, in a stainless steel r eactor and under a very pure argon atmosphere, a pyrographite sample immers ed in liquid potassium previously mixed with a very small amount of sulphur . This compound is a ternary graphite-potassium-sulphur phase, with a repea t distance of 875 pm and the chemical formula KS0.25C3. One has shown that its intercalated sheets are three-layered, according to the [K-S-K] stackin g. Both potassium planes of each intercalated sheet are hexagonal and epita xially arranged in comparison with the adjacent graphene planes, but they a re superimposed according to the AB sequence. The sulphur atoms occupy part ially (50%) the octahedral sites, which appear in the central plane of the intercalated sheet. Moreover, the structure of this intercalated potassium sulphide slice exhibits similarities with the fluorite-like cubic structure of K2S.