Electronic structure of Ni_xTiSe₂ (0.05 ≤ x ≤ 0.46) compounds with ordered and disordered Ni

Abstract

The electronic structure of the NiTiSe intercalation compounds with disordered and ordered Ni atoms is studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray spectra and density of electronic states. The increase in the covalent component of the chemical bond of Ni and Ti with the nearest neighbour was found with increasing nickel concentration and its ordering. A significant charge transfer from the Ni atoms to the host lattice resulting in the transformation of Ti into Ti occurs, while the symmetry of the crystal lattice is lowered from the hexagonal to the monoclinic one.

Electronic and crystal structure of bi-intercalated titanium diselenide CuxNiyTiSe2

“…11) are not observed upon Ti 2p-3d and Ni 2p-3d resonance excitation, although the intensity of this peak changes noticeably. Based on the results of density of states (DOS) calculations for M x TiCh 2 (M = 3d transition metal, Ch = S, Se, Te), 19,25,26,28,36 it can be assumed that the band corresponding to the T peak is formed mainly by the Se states hybridized with the Ti and Ni states. The R peak is clearly visible (Fig.…”

“…Both of these peaks are typical for the Ni x TiSe 2 system. 19 One can see that the intensity of the T peak increases with Ni concentration. The intensity of the R peak also increases with Ni concentration but does not depend on the Cu concentration (Table 4).…”

“…Details of their synthesis have been reported elsewhere. 19,20 The synchrotron radiation X-ray photoelectron (XPS), X-ray absorption (XAS) and resonant X-ray photoelectron (ResPES) spectra for Ni 0.14 TiSe 2 , Cu 0.13 Ni 0.43 TiSe 2 and Cu 0.2 Ni 0.25 TiSe 2 were obtained on the CNR IOM BACH beamline 21 at the Elettra synchrotron facility (Trieste, Italy). Linearly-polarized X-rays with a polarization vector 601 off the surface plane were used.…”

“…According to ref. 19, two Ni concentration ranges can be distinguished in Ni x TiSe 2 , in which the Se 3d binding energy slightly changes: low Ni concentrations (at x o 0.25 the Ni atoms can be considered as isolated ones), and high Ni concentrations (above x = 0.25, which corresponds to the percolation threshold of the Ti atoms coordinated by Ni). As it can be seen in Fig.…”

“…They are similar to those for the Ni y TiSe 2 system. 19 The second (with higher binding energy) Ti state appears due to the presence or absence of intercalated atoms in the second coordination sphere of Ti atoms. This is in a good agreement with the fact that the change in the Cu concentration in Cu x TiSe 2 did not affect the Ti 2p spectra.…”