Potassium-phosphorus binaries are able to intercalate into graphite as potassium-oxygen or potassium-sulphur binaries, so that phosphorus behave as a classical electronegative element. But, it is able, on the other hand, to behave as a metal such as mercury. so that potassium-phosphorus and potassium-mercury binaries intercalate into graphite by very close synthesis routes. Phosphorus appears thus as a linking element between strongly and fairly electronegative species.