Transport and Raman studies of the group IV layered compounds and their lithium intercalates: LixTiS2, LixTiSe2, LixZrS2, LixZrSe2, LixHfS2 and LixHfSe2

Resistivity and Hall coefficient measurements have been made on the lithium intercalation complexes, LixMX2, of various group IV transition-metal dichalcogenides, MX2, both during the intercalation process and after intercalation has ceased. Results for equilibrated samples are presented as a function of temperature and lithium concentration. In some materials, metallic behaviour is observed over the whole range of lithium concentration 0 < x < 1, while in others it is only observed above some critical lithium concentration. At high lithium concentrations, weak transport anomalies are seen in some materials at low temperatures, which may be related to lithium ordering or to an intralayer periodic lattice distortion (PLD). The absence of a strong PLD which exists in the isoelectronic group V material IT-TaS2 does not appear to be related to lithium-induced phonon stiffening since only small shifts in the frequencies of the Raman-active phonons are observed on intercalation.