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Measurements of the electrical resistivity have been performed on MxTiSe2 compounds intercalated with 3d metals (M = Cr, Mn, Fe, Ni) up to x = 0.5. The charge density wave (CDW) transition which is observed in pure TiSe2 below ∼200 K disappears for 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 of the resistivity in the same temperature range where the CDW transition takes place in the pure TiSe2 compound. These anomalies in highly intercalated MxTiSe2 are associated with the reappearance of a superstructure formation and associated CDW state. For Mn0.33TiSe2, the structural phase transition was evidenced from both powder neutron diffraction measurements and specific heat data. The observed results are discussed in terms of the degree of deformation of Se–Ti–Se sandwiches, which we believe play a key role in the disappearance and reappearance of the CDW state in MxTiSe2 as a function of increasing M concentration. The change in the electronic structure due to the intercalation seems not to strongly influence the presence of the CDW.

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Intercalated NixTiSe2 compounds with Ni concentration up to x = 0.5 have been investigated using x-ray diffraction, magnetic susceptibility and specific heat measurements. A set of peculiarities caused by the intercalation, such as a significant decrease of the gap between Se–Ti–Se trilayers and depletion of the low-frequency phonons due to the stiffening of the lattice as well as an enhancement of the density of electronic states at low Ni content (x < 0.33), is attributed to hybridization of the Ni 3d states with TiSe2 bands and formation of covalent-like links between Se–Ti–Se trilayers via the inserted Ni ions. NixTiSe2 compounds with intercalant content up to x = 0.5 show a paramagnetic behaviour unlike MxTiSe2 compounds intercalated by other 3d metals (M = Cr, Mn, Fe, Co). The Ni magnetic moment in NixTiSe2 is suggested to be of an itinerant nature. A pronounced correlation between the change of the lattice parameter c0 and the value of the effective magnetic moment, which is observed in NixTiSe2 as well in MxTiSe2 systems intercalated by other 3d metals, indicates that the magnetic moment on the inserted atom is controlled by the hybridization degree of M 3d states with TiSe2 bands.