Ti 3s Research Articles

Solid-state electronic structures of intercalation compounds: The system Mg(Ti 3S 4) 2

The electronic band structure of the intercalation system Mg(Ti 3S 4) 2 is investigated by a three-dimensional (3D) self-consistent-field (SCF) Hartree-Fock (HF) crystal orbital (CO) approach based on an INDO (intermediate neglect of differential overlap) all-valence Hamiltonian. The band-structure properties of Mg(Ti 3S 4) 2 are correlated with those of the binary matrix as well as the dichalcogenide TiS 2 where the transition-metal is in a higher oxidation-state. The calculated electronic-structure data of Mg(Ti 3S 4) 2 and TiS 2 are compared with available results of experimental measurements. For TiS 2 the present computational findings are furthermore compared with previous band-structure calculations. The formation of charge-density-wave (CDW) solutions in Mg (Ti 3S 4) 2 and Ti 3S 4 are analyzed. The CDW condensation is caused by fluctuating valences (i.e. deviations of an orbital occupancy around its average value) in the Ti sublattice. Some associated many-body effects are discussed. Mg(Ti 3S 4) 2 is a system where electronic and ionic conductivity are both operative. A first-order phase-transition of the insulator-semimetal type is predicted for the ternary system as a function of the spatial localization of the intercalant-atoms in the 1D van der Waals channels. Electronic reorganization-processes between the intercalant and the Ti 3S 4 matrix accompanying this phase-transition are analyzed. It is shown, that the rigid band-model is nonvalid for the interpretation of the band-structure properties of the intercalation compound. The results of frequently used methods in band-structure theory of intercalated transition metal chalcogenides are critically reviewed. The present findings render possible a reinterpretation of some electronic consequences of intercalation. Variations of the one-electron energies in intercalated materials were incorrectly predicted by methods employed conventionally in solid-state theory.

Novel low temperature synthesis of titanium sulfide

Amorphous titanium sulfides were synthesized by the direct reaction between dry organic sulfurizing agents and TiCl 4. A detailed discussion is given about the reactivity of TiCl 4 with each sulfurizing agent. All of the usual crystalline titanium sulfides phases (Ti 3S 4, TiS 2, TiS 3) were also synthesized by simply heating the obtained amorphous powder or by heating this powder in the presence of sulfur. These reactions occurred very rapidly and allowed for the simple synthesis of all the crystalline phases.

Catalytic dissociation of H 2O by SrTiO 3(100) step sites

The adsorption of H 2O on fractured and planar surfaces of SrTiO 3(100) has been studied using photoemission spectroscopy. Valence region spectra evidence molecular adsorption on the planar surface and dissociative adsorption on the fractured surface. Features arising from surface Sr (Ti) atoms on the SrO (TiO 2) terraces of SrTiO 3(100) have been resolved in core-level photoemission spectra: the surface Sr 3d (Ti 3s) features lie to lower (higher) initial energy of the bulk-derived peaks by ca. 1.0 eV (1.7 eV). These results are consistent with the expected enhancement of covalent bonding in the TiO 2-terrace surface. From the valence and core level spectra we deduce that step-sites, which connect the two types of terrace, act as catalytic centres for H 2O dissociation.

H 2O dissociation by SrTiO 3 (100) catalytic step sites

The adsorption of H 2O on fractured and planar surfaces of SrTiO 3(100) has been studied using photoemission spectroscopy. Valence region spectra evidence molecular adsorption on the planar surface and dissociative adsorption on the fractured surface. Features arising from surfaces Sr (Ti) atoms on the SrO (TiO 2) terraces of SrTiO 3(100) have been resolved in core-level photoemission spectra: the surface Sr 3d (Ti 3s) features lie to lower (higher) initial energy of the bulk-derived peaks by ca 1.0 eV (1.7 eV). These results are consistent with the expected enhancement of covalent bonding in the TiO 2-terrace surface. From the valence- and core-level spectra we deduce that step-sites, which connect the two types of terrace, act as catalytic centres for H 2O dissociation.

Formation of local magnetic moments in (V, Ti) 3S 4

The system of V 1−xTi xS 1.40 has been studied through magnetic susceptibility and NMR measurements. The Curie constant increases with quadratic dependence on the composition x within the V 3S 4 phase (0 ≤ x ≤ 0.6) and then, rapidly decreases toward the Ti 2S 3 phase (0.8 < x ≤ 1.0). The NMR absorption from V 51 nuclei with itinerant delectrons rapidly decreases with increasing Ti content in the former phase. These phenomena may indicate that local magnetic moments are formed in this system under a particular environment of vanadium atoms proposed. Metal distribution of V and Ti is also discussed.

Molecular orbital study of satellites in XPS spwctra of BaTiO 3 and TiO 2

XPS satellites of the main peaks (Ti 2p 1 2 ,Ti 2p 3 2 ,Ti 3s. Ti 3p, Ba4d. etc ) are observed in both BaTiO 3 and TiO 2 spectra near 5.0, 6.2, 13.2 and 25 eV The contributions or charge transfer transitions (shake-up) to the peaks at 6.2 eV and 13.2 cV are pointed out (1t 2g-2t 2g and 3e g-4e g, respectively) while energy losses are involved in the four peaks.

An electron microscope study of some titanium sulphides

Crystals of titanium sulphides of nominal composition Ti 1.25S 2 (Ti 5S 8), Ti 1.50S 2 (Ti 3S 4), and Ti 1.60S 2 (Ti 4S 5) have been prepared and studied by transmission electron microscopy. Lattice fringe resolution has shown faulting to be commonplace in the Ti 1.25S 2 and Ti 1.50S 2 compositions, but infrequent in the Ti 1.60S 2 material. In all crystals, repeat distances between lattice fringes have been found which do not correspond to previously reported titanium sulphides and are considered to arise from new structures. Diffraction evidence supports this view. Although it is likely that the existence of these new structures is due to different titanium to sulphur stoichiometries, the possibility that they are polytypes or due to impurities is also considered.

The system titanium-sulfur. II. The structures of Ti 3S 4 and Ti 4S 5

The crystal structures of rhombohedral Ti 3S 4 and hexagonal Ti 4S 5 were determined by X-ray powder diffraction methods. The structures are based on close packings of sulfur atoms of the types ( chchchh) 3 and ( chchh) 2, respectively; the metal atoms lie in part of the octahedral holes of these packings. The occupancies of the various metal positions were determined; they can be described by occupation waves. Correlations of the compositions of titanium sulfides in the range Ti 2S 3TiS with the observed interatomic distances, stacking sequences and occupation waves are given and discussed.