Neutron diffraction and small-angle scattering studies of graphite-nickel chloride intercalation compounds

Intercalation of graphite with metal chlorides leads to compounds for which chemical analyses give non-integer stoichiometric coefficients. In particular, an excess of chlorine is observed with respect to free metal chlorides. For NiCl2 intercalated graphite, the composition of the second-stage compound corresponds to the formula: Csub(11.3)NiClsub(2.13). This chlorine excess was accounted for by assuming the existence of small islands of intercalated chloride. As NiCl2-graphite compounds are known to undergo a magnetic phase transition at about 20 K, neutron scattering and diffraction experiments were carried out in order to provide evidence for the islands and to specify the magnetic ordering at low temperature. From the small-angle scattering data collected below and above the magnetic transition, the first experimental evidence for the presence of intercalated islands has been obtained. The mean size of the islands is about 150 A, as previously assumed. From diffraction experiments, it has been shown that the spins of Ni2+ ions in the magnetic phase are aligned ferromagnetically within the intercalant layer. (Auth.)