Alkali metal intercalates of molybdenum disulfide

Abstract

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 K_0.4MoS₂ and Rb_0.3MoS₂ was achieved. The x‐ray results show insignificant changes in the a_o axis and considerable expansion of c_o axis after intercalation (Δc_o : 6.745, 2.704, 4.286, 4.899, and 7.312 Å for Li_0.4MoS₂, Na_0.3Mos₂, K_0.4MoS₂, Rb_0.3MoS₂, and Cs_0.3MoS₂, respectively). All intercalated crystals were superconducting (T_onset: 3.7, 4.1, 6.1, 6.25, and 6.30 for Li_0.4MoS₂, Na_0.3MoS₂, K_0.4MoS₂, Rb_0.3Mos₂, and Cs_0.3MoS₂, 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.