Alkali metal intercalates of molybdenum disulfide

Natural molybdenite and single crystals of MoS2 grown by chemical vapor transport were intercalated with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Stoichiometries and x-ray data of all intercalates were determined and a complete indexing of the x-ray patterns of K0.4MoS2 and Rb0.3MoS2 was achieved. The x-ray results show insignificant changes in the ao axis and considerable expansion of co axis after intercalation (Δco : 6.745, 2.704, 4.286, 4.899, and 7.312 Å for Li0.4MoS2, Na0.3Mos2, K0.4MoS2, Rb0.3MoS2, and Cs0.3MoS2, respectively). All intercalated crystals were superconducting (Tonset: 3.7, 4.1, 6.1, 6.25, and 6.30 for Li0.4MoS2, Na0.3MoS2, K0.4MoS2, Rb0.3Mos2, and Cs0.3MoS2, respectively). The superconductivity is believed to be due to an electron transfer from the alkali metal to an empty band of MoS2, resulting in an increase in electron density as well as in the density of states at the Fermi surface.