Suppression and inducement of the charge-density-wave state in Cr x TiSe2

The x-ray diffraction, electrical resistivity and thermal expansion measurements have been employed to study how the intercalation of Cr atoms into TiSe2 matrix affects the crystal structure, formation of the charge density wave (CDW) and electrical properties. The intercalation of a small amount of Cr atoms (up to x ~ 0.03) is observed to suppress the CDW formation. The electrical resistivity of Cr x TiSe2 compounds with the Cr concentrations 0.03  ⩽  x  ⩽  0.20 shows a metallic-type behavior; while in the concentration range 0.25  ⩽  x  ⩽  0.5, the resistivity shows an anomalous behavior indicating the reappearance of the transition to a CDW-like state; further growth of the Cr content up to x  =  0.6 again leads to the metallic-type resistivity. For the compound Cr0.25TiSe2, the phase transition below 160 K together with abnormal change in the electrical resistivity is found to be accompanied by anomalies in the lattice parameters and thermal expansion behavior; this transition is classified as first-order type. It has been found that despite the intercalation of Cr atoms some Ti-Se bonds in the Se-Ti-Se tri-layers of Cr x TiSe2 with x  ⩽  0.5 have nearly the same lengths as in the host lattice TiSe2, which apparently allows the transition to be returned to the CDW-like state.