Structural and electronic study of KHg and RbHg intercalated graphite

Abstract

We have shown that the potassium and rubidium amalgams, KHg and RbHg, intercalate into graphite forming very metal-rich ternary compounds of general formula MHgC 4 (first stage) and MHgC 8 (second stage). The reaction provokes a very high c axis dilation of the host graphite: 203% for KHg and 221% for RbHg in first stage products, attributed to the three-layer structure of the intercalant. Two planes of the alkali metal atoms are epitaxied on the carbon layers on either side of a mercury layer. These latter atoms occupy prismatic sites created by the strictly defined disposition of the former. A study of certain electronic properties has been undertaken. Room temperature values of electrical resistivity are higher than those of the corresponding alkali metal compounds: about 20 μ cm for first stage products and about 12 μ cm for second stage products. The variation with temperature down to 100 K has been measured yielding values smaller by a factor of about five than the ambient temperature values. The compounds possess a Pauli paramagnetic type of susceptibility, practically temperature independent from 4.2 to 300 K. The first stage compounds can give solid solutions, K x Rb 1− x HgC 4 for which the average magnetic susceptibility shows a quite pronounced minimum as a function of composition.