S. G. Titova

Charge carriers localization in intercalation compounds based on dichalcogenides of titanium

Abstract X-ray photoemission study for FexTiTe2 and investigation of thermodynamic functions for AgxTiTe2 were carried out. It was shown that intercalation of Ag and Fe into TiTe2 leads to a rising of a narrow band at the Fermi level, probably due to appearance of the covalent “bridges” between the host lattice layers.

Determination of the polaron shift in titanium diselenide-based intercalation compounds

A study is reported of the dependence of the TiSe2 lattice constants on the concentration of an intercalated metal in various valence states and external pressure. The strain energy and the polaron shift created in the intercalation of TiSe2 with metals in various valence states have been determined. The position of the polaron band is shown to decrease linearly with the increasing intercalant ionization potential.

Hierarchy of percolation thresholds and the mechanism for reduction of magnetic moments of transition metals intercalated into TiSe2

The concentration dependences of the effective magnetic moment of transition metal atoms intercalated into TiSe2 are analyzed in the framework of the percolation theory. It is shown that, depending on the degree of localization of impurity states, the effective magnetic moment is determined by the overlap of 3d orbitals of transition metals or orbitals of titanium atoms coordinated by impurity atoms.

The influence of intercalation on the phonon spectrum of titanium dichalcogenides

A systematic investigation of the inelastic neutron scattering spectra is carried out for intercalation titanium diselenide compounds of the general formula MxTiSe2 (M = Cr, Fe, Ni, Ag). It is shown that the effect of intercalation on the phonon spectrum of the material is determined primarily by the modification of the host lattice due to the formation of Ti-M-Ti covalent centers. It is established that the lattice can undergo a substantial softening when the impurity band coincides with the Fermi level.

Mechanism of thermal decomposition of the nonstoichiometric compound YBa2Cu3O6.8

Thermal decomposition of the nonstoichiometric high-temperature superconductor YBa2Cu3O6.8 at a temperature of 200°C in air has been investigated using the full-profile analysis of X-ray diffraction lines. Two mechanisms of decomposition are revealed. The first mechanism, i.e., separation into two phases with a different oxygen content, occurs continuously. The second mechanism, i.e., disordering of the heavy atoms Y, Ba, Ba, Y along the crystallographic axis c, begins to occur after a 20- to 35-h annealing and progresses with a further annealing.

Deformation-intensified atomic separation in bcc Fe–Mn alloys

The deformation-intensified atomic Mn-related separation of the bcc solid solution has been found in Fe100–xMnx alloys (x = 4.5–9.9) subjected to ball milling using Mössbauer spectroscopy. In the near surrounding of iron atoms, the atomic separation is similar to that observed upon the annealing of the alloys in a temperature range of 400–500°С. It has been found that the deformation-intensified atomic separation leads to the stabilization of the bcc phase with regard to the α → γ transformation, as well as to the expansion of the field of the existence of the bcc phase during heating.

Structural and Physical Properties of Cobalt-Intercalated Titanium Diselenide and Ditelluride Compounds

A complex investigation of the structural, electrical, and magnetic properties of cobalt-intercalated titanium diselenide and ditelluride compounds at different intercalant concentrations and temperatures is performed for the first time. The influence of the matrix on the physical characteristics of the intercalation materials is analyzed.

Localization of charge carriers in materials with high polaron concentration

The influence of polaron concentration on the type of transition from band to activate conductivity has been investigated. For a single polaron in the crystal lattice or for material with polaron concentration higher than the percolation threshold, such a transition is continuous, in accordance with theory. However, for intermediate cases this process becomes step-like, because the rapid increase of density of states at Fermi level leads to a change of polaron characteristics. These suppositions are illustrated by experimental results (XPS-spectra, crystal structure analysis, DC conductivity) for intercalation compounds based on titanium dichalcogenides.

Thermal stability of nonstoichiometric ceramic YBa2Cu3O6.8 at 200°C in a dried air

The behavior of the nonstoichiometric ceramic YBa2Cu3O6.8 has been investigated during annealing at a temperature of 200°C in an atmosphere excluding the penetration of water into the sample. It has been found that, under these conditions, the separation into two phases with different oxygen contents proceeds extremely weakly. The previously observed disordering of Y and Ba atoms along the crystallographic axis c occurs under the effect of the OH− group formed on the crystallite surface as a result of dissociation of water in the case of treatment in the undried atmosphere.

Synthesis and investigation of titanium diselenide intercalated with ferrocene and cobaltocene

Single crystals and polycrystals of titanium diselenide TiSe2 intercalated with ferrocene Fe(η5-C5H5)2 and cobaltocene Co(η5-C5H5)2 are synthesized. The magnetic susceptibility and electrical resistivity of the intercalation compounds are measured. The results obtained demonstrate that the intercalation brings about the formation of an impurity band with a temperature-dependent width.