Possible reappearance of the charge density wave transition inMxTiSe2 compounds intercalated with 3d metals

Abstract

Measurements of the electrical resistivity have been performed onMxTiSe2 compounds intercalatedwith 3d metals (M = Cr,Mn, Fe, Ni) up to x = 0.5. The charge density wave (CDW) transition which is observed in pureTiSe2 below∼200 K disappearsfor intercalation x>0.1, while a further increase of the intercalant content(x≥0.25,M = Cr, Mn or Fe) leads to the appearance of pronounced anomalies in the temperature dependences ofthe resistivity in the same temperature range where the CDW transition takes place in the pureTiSe2 compound. These anomalies in highly intercalatedMxTiSe2 are associated with the reappearance of a superstructure formation and associated CDW state. ForMn0.33TiSe2, the structural phase transition was evidenced from both powder neutron diffractionmeasurements and specific heat data. The observed results are discussed interms of the degree of deformation of Se–Ti–Se sandwiches, which we believeplay a key role in the disappearance and reappearance of the CDW state inMxTiSe2 as a function of increasing M concentration. The change in the electronic structure dueto the intercalation seems not to strongly influence the presence of the CDW.