2H-MoS2 is a semiconductor with a hexagonal layered structure. Each Mo atom is prismatically coordinated by six S atoms. Our in situ X-ray diffraction results indicate that, upon intercalation, the MoS2 host lattice undergoes a first order phase transition in which the Mo coordination changes from trigonal prismatic to octahedral (1T structure). The driving mechanism for this structural change is discussed in terms of a charge transfer from the lithium to the host and in terms of the respective energy-band diagrams for 2H and 1T polytypes. Intercalation-induced reversals in the relative stability of trigonal–prismatic and octahedral phases may also be expected in other semiconducting hosts.

We describe powder X-ray diffraction experiments on lithium intercalation compounds. Using a unique electrochemical cell which incorporates a beryllium X-ray window we are able to monitor changes in the host lattice which occur when the lithium concentration is altered electrochemically. The detailed design of the cells and experimental problems which arise when using the in situ X-ray diffraction technique are discussed. Results of experiments on LixTiS2 are reported for 0 ≤ x ≤ 2.

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