Determination of the Critical Points for Intercalating Systems by the EMF Method Concerning Foreign Metal

The work is devoted to the study of the possibility of determining the critical points of phase diagrams by measuring the EMF of electrochemical cells relative to a metal that is not part of the test substance. The measurement results of the concentration dependences of the EMF for the Cu_xTiS₂ system in the electrochemical cells Na|Na⁺|Cu_xTiS₂ and Cu|Cu⁺|Cu_xTiS₂ in the concentration range 0 < x < 0.7 are compared. It was determined that the chemical potential of the ion is independent of x in a satisfactory approximation. The EMF difference in the given cells is close to the standard electrode potentials difference for respective metals. It is concluded that the dependences E(x) for both types of cells are similar and correlated. Therefore, one can choose any convenient metal for measurements of this kind. Using the example of measuring EMF in electrochemical cells for the Fe_xTiSe₂ system concerning sodium and lithium, we showed that the elastic contribution to free energy is constant over the entire concentration range 0 < x < 0.5.

Specific features of the electronic structure of CoxTiSe2 according to the resonant photoemission data

The effect of atomic ordering in the Co sublattice on the electronic structure of the Co_xTiSe₂ compounds has been studied using a complex of spectral techniques – XPS, XAS, and ResPES, along with theoretical calculations of the total and partial DOS.

Chemical bonds in intercalation compounds CuxTiCh2 (Ch = S, Te)

A thorough study of the chemical bonding between intercalated copper and host lattice TiCh₂ (Ch = S, Te) was performed. In order to separate the contributions of the copper, titanium, and chalcogen states into the electronic structure of the valence band, photoelectron spectroscopy in nonresonant and resonant (Cu 3p-3d and Ti 2p-3d) excitation modes was used. It is shown that the ionicity of the chemical bond between copper and host lattice is decreased in the TiS₂ → TiSe₂ → TiTe₂ row. In Cu_xTiS₂, copper atoms form the chemical bond with TiCh₂ host lattice, while in Cu_xTiTe₂ directly with tellurium atoms.

Thermal stability of the layered modification of Cu0.5ZrTe2 in the temperature range 25-900 °C

The thermal stability of the layered modification of the Cu_0.5ZrTe₂ polycrystalline intercalation compound, synthesized at room temperature, has been studied in the temperature range 25-900 °C. A change in the occupation of the octahedral and tetrahedral coordinated sites in the interlayer space of the zirconium ditelluride was observed using in-situ time-resolved synchrotron X-ray powder diffraction experiments. The formation of the rhombohedral CuZr₂Te₄ phase, which is stable in the temperature range 300-700 °C, has been observed. The copper intercalation at room temperature leads to the formation of a phase in which the Cu atoms occupy only octahedral sites in the interlayer space. At temperatures above the decay temperature of the rhombohedral CuZr₂Te₄, a layered phase with Cu atoms uniformly distributed between octahedral and tetrahedral sites in the interlayer space is stable. The changes in the crystal structure independent of temperature are in agreement with the previously proposed model, according to which the stability of the layered or the rhombohedral phase is determined by the entropy factor associated with the distribution of the intercalated atoms between the octahedral and tetrahedral sites in the interlayer space.

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.

Electronic structure of VxTi1-xSe2 in wide concentration region (0.06 ≤ x ≤ 0.9)

An experimental study of the electronic structure of V_xTi_1-xSe₂ system in a wide range of vanadium concentrations (x = 0.06-0.9) using x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy has been performed. The partial charge transfer from the VSe₂ to TiSe₂ structural fragments is experimentally observed, and the most part of the charge is localized on the vanadium atoms in the VSe₂ structural fragments.

Electronic structure of NixTiSe2 (0.05 ≤ x ≤ 0.46) compounds with ordered and disordered Ni

The electronic structure of the Ni_xTiSe₂ 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 Ti⁴⁺ into Ti³⁺ occurs, while the symmetry of the crystal lattice is lowered from the hexagonal to the monoclinic one.

The electronic structure formation of Cu(x)TiSe2 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 = 0.04-0.8) 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.

Resonant photoemission at the L3 absorption edge of Mn and Ti and the electronic structure of 1T-Mn0.2TiSe2

Resonant valence band x-ray photoelectron spectra (ResPES) excited near the 2p(3/2) core level energies, 2p x-ray photoelectron spectra (XPS) and L(3,2) x-ray absorption spectra (XAS) of Ti and Mn in single crystals of 1T-Mn(0.2)TiSe(2) were studied for the first time. The ionic-covalent character of the bonds formed by the Mn atoms with the neighboring Se atoms in the octahedral coordination is established. From the XPS and XAS measurements compared with the results of atomic multiplet calculations of Ti and Mn L(3,2) XAS, it is found that the Ti atoms are in the ionic state of 4 + and the Mn atoms are in the state of 2 +. In ResPES of Mn(0.2)TiSe(2) excited near the Ti 2p(3/2) and Mn 2p(3/2) absorption edges the Ti 3d and Mn 3d bands at binding energies just below the Fermi level are observed. According to theoretical calculations of E(k) the Ti 3d states are localized in the vicinity of the Γ point and the Mn 3d states are localized along the direction K-Γ-M in the Brillouin zone of the crystal.