A. S. Shkvarin

Electronic structure of titanium dichalcogenides TiX 2 (X = S, Se, Te)

The electronic structure and the chemical bond in titanium dichalcogenides TiX2 (X = S, Se, Te), which are promising electrode materials for lithium batteries, are studied experimentally and theoretically. It is found that the X-ray photoelectron spectra of the valence bands and the core levels of titanium and its X-ray L2, 3 absorption spectra demonstrate a change in the ionic and covalent components of the chemical bond in these compounds. The densities of states in these compounds are calculated by the full-potential augmented-plane-wave method, and multiplet calculations of the X-ray L2, 3 absorption spectra of titanium are performed. It is shown that, in the row TiS2-TiSe2-TiTe2, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

Localization of charge carriers in layered crystals MexTiSe2 (Me = Cr, Mn, Cu) studied by the resonant photoemission

The probability of charge transfer in layered titanium diselenide between monolayers containing Cr, Mn, and Cu with different concentrations and host lattice TiSe2 is estimated according to the resonant photoemission data. For this purpose, the Raman-Auger contributions and narrow bands just below the Fermi energy were separated in the valence band spectra. These contributions provide the information about charge transfer. It is shown that the localization of the 3d electrons is typical for Cr and Cu atoms and strongly depends on theirs concentration. In MnxTiSe2, Mn 3d electrons are delocalized and the probability of the charge transfer is the greatest as compared with other compounds under investigation.

Resonant photoemission and absorption spectroscopy of the CuxTiSe2 compound

Single crystals of the CuxTiSe2 compound with x = 0.05, 0.09, and 0.33 have been grown. Resonance photoelectron Cu 3p-3d and 2d-3d spectra of the valence bands, the spectra of the core levels, and the L absorption spectra for titanium and copper have been obtained. It is shown that the degree of oxidation of titanium atoms is +4 and the state of copper atoms is close to the state of free copper ions. It is found that the spectra of the valence bands obtained under the Cu 3p and 2p resonance conditions radically differ. For the spectra in the Cu 2p excitation regime, several bands corresponding to different decay channels of the excited state are observed. According to calculations of the density of states, the 3d states of copper are filled incompletely; the occupancy of the 3d band of copper is 9.5 electrons per atom.

An X-ray spectrscopy study of the electronic structure of TiS3

X-ray photoemission and absorption spectra of TiS3 are studied. The temperature dependence of the magnetic susceptibility is measured and the electron density of states is calculated. Titanium ions in different oxidation states are found to coexist.

The electronic structure formation of CuxTiSe2 in a wide range (0.04 < x < 0.8) of copper concentration

An experimental study of the electronic structure of copper intercalated titanium dichalcogenides in a wide range of copper concentrations (x = 0.05 - 0.6) using the x-rays photoemission spectroscopy, resonant photoemission and x-rays absorption spectroscopy has been performed. Negative energy shifts of the Ti 2p and Se 3d core levels spectra and a corresponding decrease of the photon energy in Ti 2p absorption spectra with increasing concentration of copper have been found. Such sign-anomalous shifts may be explained by the shielding effect of the corresponding atomic shells as a result of the dynamic charge transfer during the formation of a covalent chemical bond between the copper atoms and the TiSe2 matrix.An experimental study of the electronic structure of copper intercalated titanium dichalcogenides in a wide range of copper concentrations (x = 0.04-0.8) using x-ray photoelectron spectroscopy, resonant photoelectron spectroscopy, and x-ray absorption spectroscopy has been performed. Shift towards low energies of the Ti 2p and Se 3d core level spectra and a corresponding decrease in the photon energy of Ti 2p absorption spectra with the increase in copper concentration have been found. These sign-anomalous shifts may be explained by the shielding effect of the corresponding atomic shells as a result of the dynamic charge transfer during the formation of a covalent chemical bond between the copper atoms and the TiSe2 matrix.

Studying the electronic structure of CrxTi1−xSe2 by X-ray resonance and absorption spectroscopy

CrxTi1 − xSe2 (x = 0–0.83) solid solutions have been synthesized. Single crystals have been grown in the range of concentrations x = 0–0.83. Structural studies of samples have revealed that chromium atoms substitute titanium in the TiSe2 matrix. The X-ray photoelectron spectra of the core levels, the resonance spectra of the valence bands in 1T-CrxTi1 − xSe2, and the X-ray absorption spectra of titanium and chromium are studied. The titanium and chromium atoms are shown to have oxidation numbers of +4 and +3, respectively, in an identical octahedral environment. The local density of chromium states has been calculated. The results of the calculation agree well with the experimental data and indicate that the electronic 3d states of chromium substituting titanium in the matrix are spin-polarized and the density of chromium states is halfmetal magnet in behavior.

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS2, TiSe2, and TiTe2 dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS2 and TiTe2. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS2, TiSe2, and TiTe2 compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS2 is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe2 is caused by occupation of the 3d band in Ti.

MxTiSe2 (M¼Cr, Mn, Cu) electronic structure study by methods of resonance X-ray photoemission spectroscopy and X-ray absorption spectroscopy

Electronic structure and chemical bonding in TiX2 (X=S, Se, Te), TMxTiSe2 (TM=Cr, Mn, Cu) and CrxTi1-xSe2 were studied by x-ray resonance photoemission and absorption spectroscopy. These methods are detected to be strong sensitive to chemical bonding. Charge transfer from the intercalated atoms to Ti 3d band is detected. Narrow Ti 3d and Cu 3d bands are observed under Fermi level in CuxTiSe2.

Resonant photoemission and absorption spectroscopy study of the Cr x Ti 1− x Se 2 electronic structure

Solid solutions of 1T-CrxTi1−xSe2 (x = 0−0.83) were synthesized for the first time. To study the electronic structure of CrxTi1−xSe2 monocrystals, photoemission spectra of core levels, resonance spectra of valence bands, and absorption spectra of Ti and Cr were obtained. Titanium and chromium atoms were found to have the oxidation state 4+ and 3+, which is supported by atomic multiplet calculations for Ti and Cr in the octahedral environment. According to calculation of the local density of chromium electronic states, the Cr3d electrons are spin-polarized, and the density of chromium states is of half-metal nature. The calculation agrees well with the experimental data.

Electronic structure of ZrX2 (X = Se, Te)

The electronic structure of the ZrX2 (X = Se, Te) compounds has been studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray absorption spectra, and density of electronic states. It was found that the absorption spectra and valence band spectra are influenced by the chalcogen type. The results of the multiplet calculation of the Zr4+ atom show that the change in the splitting in the crystal field, which is described by the 10Dq parameter, is due to the change in the ratio of covalent and ionic contributions to the chemical bond. The resonance band near the Fermi level in the valence band spectra is observed for ZrTe2 in the Zr 3p-4d resonant excitation mode. The extent of photon energy indicates the charge localization on the Zr atom. Similar resonance band for ZrSe2 is absent; it indicates the presence of a gap at the Fermi level.