text: One of the best studied graphite intercalation compounds, , is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite.  is a superconductor with a very low critical temperature T = 0.14 K. Heating  leads to the formation of a series of decomposition products as the K atoms are eliminated:
  Via the intermediates  (blue in color), , , ultimately the compound  results.
  The stoichiometry  is observed for M = K, Rb and Cs. For smaller ions M = , , , , , and , the limiting stoichiometry is . Calcium graphite  is obtained by immersing highly oriented pyrolytic graphite in liquid Li–Ca alloy for 10 days at 350 °C. The crystal structure of  belongs to the Rm space group. The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524 Å, and the carbon-carbon distance increases from 1.42 to 1.444 Å.
  With barium and ammonia, the cations are solvated, giving the stoichiometry ((stage 1)) or those with caesium, hydrogen and potassium ((stage 1)).
  In situ adsorption on free-standing graphene and intercalation in bilayer graphene of the alkali metals K, Cs, and Li was observed by means of low-energy electron microscopy.
  Different from other alkali metals, the amount of Na intercalation is very small. Quantum-mechanical calculations show that this originates from a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same group of the periodic table. The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table. However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation. A complex magnesium(I) species has also been intercalated into graphite.