Electrical and magnetic properties of titanium diselenide intercalated with cobalt

This paper discusses experimental studies of the temperature dependence of the magnetic susceptibility, electrical conductivity, and Seebeck coefficient of the compounds Co_xTiSe₂ (0.1⩽x⩽0.5), along with the structural behavior exhibited by these compounds. For Co_0.5TiSe₂, the observed temperature dependence of the magnetic susceptibility is characteristic of an antiferromagnet with a Néel temperature of 510 K. The data obtained on the structural characteristics and physical properties of the intercalated phases are interpreted using a model that assumes the formation of bands of localized states near the Fermi level. Fiz. Tverd. Tela (St. Petersburg) 39, 1618–1621 (Sepember 1997)     

Magnetic susceptibility of titanium diselenide intercalated with copper

The temperature dependence of the magnetic susceptibility of Cu _x TiSe₂ polycrystalline samples has been measured. The electron density of states near the Fermi level N(E _F) in the Pauli model of paramagnetism has been calculated and discussed. The concentration dependences of the density of states N(E _F) and the unit cell parameter in the direction perpendicular to the layers in Cu _x TiSe₂ correlate with the concentration of centers V-Ti-Cu and Cu-Ti-V (V is the vacancy).     

Anomalies in the structure and properties of titanium diselenide intercalated by iron

The transition between the heavy and localized polaron modes in the Fe _x TiSe₂ compounds used as an example is studied by methods of thermal analysis, neutron diffraction, and dc conductivity. It is found that the transition under investigation is accompanied by an anomaly in the behavior of the crystallographic parameters. The changes observed in the character and magnitude of the electrical conductivity at a higher temperature, as well as the thermal effect, are attributed to thermal broadening of the polaron band. The difference between the data for Fe _x TiSe₂ and the previously obtained results for Ag _x TiTe₂ correlates with the difference in the binding energies of the polaron bands in these materials.     

Structural characteristics and physical properties of manganese-intercalated titanium diselenide

This paper reports on an experimental study of the concentration and temperature dependences of the structural parameters, as well as of the electrical and magnetic properties, of manganese-intercalated titanium diselenide. The effect of manganese on the properties of the compounds produced by its intercalation between Se-Ti-Se layers is shown to differ strongly in character from those of other guest 3d elements. The results obtained are interpreted with account taken of the specific features of the manganese electronic structure.     

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.     

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.     

Kinetics of reactions in interlayer space of titanium diselenide intercalated with iron

Decomposition of a homogeneous intercalation compound with the formation of inclusions in the interlayer space of a matrix lattice has been directly observed. In full compliance with previously advanced theoretical concepts, it has been shown that the decomposition is accompanied by metallic iron extraction, which then gradually transforms into iron selenide due to the interaction with gaseous selenium.The hierarchy of diffusion mobilities of various defects in Fe_xTiSe₂ intercalation compound has been determined. It has been found that the largest mobility is inherent to intrinsic defects of the TiSe₂ lattice, i.e., vacancies in Ti and Se sublattices. The phenomenon of dissociation pressure oscillations as a function of time has been detected. This phenomenon has been explained by the existence of a slow decomposition stage, i.e., intercalated iron diffusion during the formation and dissolution of its inclusions as an individual phase.     

Dependence of the physical properties of pure and lithium intercalated zirconium diselenide on the host lattice stoichiometry

X-ray, conductivity, susceptibility and NMR measurements have been performed on pure and lithium intercalated zirconium diselenide Li_xZrSe_y in the stoichiometry range 1.85 < y < 1.95. It is shown that the pure host conductivity behaves as metallic for y < 1.90 and as semiconducting for y > 1.91. Occurence of lattice expansion upon intercalation for a threshold x value has been confirmed by neutrons diffraction measurements with y = 1.95 and it is found that this threshold x value depends on the stoichiometry y of the host matrix. Previous works are discussed in view of these results which give evidence for interactions between the intercalated lithium and the stoichiometry defects.     

Structure and physical properties of gallium selenide laser-intercalated with nickel

Intercalated crystals of indium and gallium selenide are prepared. It is shown that laser intercalation of nickel into GaSe samples leads to a giant magnetoresistive effect whose magnitude and sign depend on the concentration of the guest component. The giant magnetoresistive effect in the InSe intercalation compounds is considerably weaker and does not exceed 5%. The experimental data obtained are explained in terms of magnetic delocalization (localization) of charge carriers with the participation of states of intercalated magnetically active atoms in the vicinity of the Fermi level.     

Phase transitions in titanium diselenide intercalated with cobaltocene at high pressures of up to 20 GPa

The pressure dependences of the kinetic properties of TiSe₂ intercalated with cobaltocene (biscyclopentadienyl-cobalt, CoCp ₂) and cobaltocene itself were measured. Anomalies are revealed in the pressure dependences of the resistance and thermopower (for the intercalated material), which are interpreted as pressure-induced structural phase transitions. The main effect of pressure on the molecules of cobaltocene as an individual compound and in the intercalated state is suppression of the intramolecular motion in the form of rotation of the cyclopentadienyl rings. The general character of the pressure effect on the kinetic properties of (CoCp ₂) _x TiSe₂ agrees well with the assumption that the bonding of the organic molecules to the host lattice is covalent.     

Structure and properties of the bronze laser alloyed with titanium

The paper describes the microstructure and properties (microhardness and wear resistance) of the bronze laser alloyed with titanium. The laser alloying was done using a pulsed Nd:YAG laser with a generated beam energy of 25-35 J. A very fine microstructure was formed under such rapid solidification conditions like laser treatment. The high chemical homogeneity and fine structure of the melted zone were attributed to high cooling rates due to the short interaction time with Nd:YAG pulsed laser radiation and relatively small volume of the melted material. The structure obtained in the surface layer after laser alloying permits to get a high level of hardness and an improved wear resistance.     

Anomalous properties of cobalt diselenide

From N.M.R. and X-rays experiments we show that the anomalous temperature dependence of the bulk magnetic susceptibility of cobalt diselenide which was first attributed to the occurence of antiferromagnetism is rather due to some structural instability. This is supported by an observed anomaly in the thermal variation of the lattice parameter and a (Tm-T)${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ thermal variation of the ⁷⁷Se N.M.R. linewidth (Tm ～ 50K is the temperature at which the instability occurs). Such behaviour has already been observed in CuS₂ and layered NbSe₂ where structural instabilities are known to occur. Some off-stoichiometry effects are     

Structure and physical properties of liquid crystals

In writing this review article on the “state of the art” in liquid crystals we assume that the reader has an acquaintance with the fundamentals of the subject. For those who may wish to start with more elementary and general material we cite two articles.     

Structure and properties of the physical vacuum

The structure and properties of the vacuum medium are investigated on the basis of the random flight of elementary particles along space quanta. It is shown that on the whole the vacuum medium, being the basis of the forming and propagation of electromagnetic waves, constitutes an incompressible two-component superfluid having positive and negative mass densities. A system of equations is set up describing the properties of this fluid; the energy and temperature characteristics of the vacuum medium are introduced. The structure of the space quantum is determined as Cooper electron-positron pairs, the energy of this bond and, consequently, the creation energy of elementary particles, is determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 60–65, January, 1985.     

The effect of intercalation by 3d elements on the structure and physical properties of titanium diselenide MxTiSe2 (M=Cr, Fe, Co)

The dependences of the structural parameters and the electrical and magnetic properties of titanium diselenide, intercalated by chromium, iron, and cobalt on the intercalant concentration and temperature were studied experimentally. The possibility of the involvement of d electrons in the formation of interlayer covalent bonds in relation to the 3d-shell filling of intercalated ion is discussed.     

High-pressure synthesis and physical properties of new iron (nickel)-based superconductors

We have utilized a high-pressure (HP) technique to synthesize a series of newly-discovered iron (nickel)-based superconductors. For the LnFeAsO-based superconductors (Ln = lanthanide), we show that the introduction of oxygen (O)-deficiency in the LnO layers, which is achievable only through HP process, is an effective way to dope electron carriers into the system, which results in yielding the superconducting transition temperature (T_c) comparable with those for F-substituted counterpart. The effect of O-deficiency, variation of Ln ions, and the external pressure on T_c are examined. All the experimental data indicate strong correlation between the crystal structure and the superconductivity of the oxypnictide superconductors. Upper critical field measurement on single crystalline sample of PrFeAsO_1?y shows the superconducting anisotropy of 5, which is smaller than cuprates. We also demonstrate that HP technique is applicable for the so-called ‘122’ systems, by showing the results on polycrystalline (Ca, Na)Fe₂As₂, (Ba, K)Fe₂As₂, as well as single crystal BaNi₂P₂ samples.