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The influence of the selective distortion of the Se and Ti sublattices on the stability of the charge-density-wave (CDW) state has been studied. The selective distortion has been obtained in two ways: by Mn or Cr intercalation, which differ in the selective hybridization between Mn 3d/Se 4p and Cr 3d/Ti 3d orbitals, and by the plastic uniaxial deformation of the TiSe 2 single crystals. Plastic deformation generates defects in the Se sublattice, which create the difference between the nearest neighbor positions. It is found that the distortions of the Se sublattice make impact up to 1000 times more on the CDW state stability than those of the Ti sublattice. The effect is related to the distortion of the spatial coherence of the Se 4p-orbitals. The critical size of the coherence area, below which the CDW becomes unstable structure and loses a long-range-order, has been estimated. It is found that such a kind of suppression does not change the temperature of the CDW transition but gradually decreases its amplitude. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the charge transfer characteristics and electronic structure of ferrocene-intercalated TiSe2. The spectroscopic results revealed that an intercalation of metallocene molecules leads to changes in the ionic valence of Fe atom in ferrocene molecule and the band gap, which is in accordance with electrical resistivity measurements showing metallic conductivity. Our analysis of 57Fe Mössbauer and Fe 2p XAS spectra suggested that the suppression of charge-density-wave state in TiSe2 and an appearance of metallic conductivity are attributed to charge transfer of electrons from ferrocene intercalant to the dichalcogenide host material. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

The comparison of the electronic structure modifications of intercalation materials at intercalated metal ordering has been performed depending on the degree of metal d-shell filling using the Fe x TiSe 2 and V x TiSe 2 . The crystal and electronic structure of the V x TiSe 2 compounds has been studied for the first time. The electronic structure based on experimentally obtained atomic parameters has been calculated by the first principle approach. Obtained results are discussed taking into account an order of both intercalated atoms and vacancies. It has been shown that ordering leads to the formation of additional bands, the energy and orbital symmetry of which are determined by the electronic configuration of the intercalated metal ion. [ABSTRACT FROM AUTHOR]

The structure, electrical resistivity, thermopower, and magnetic susceptibility of titanium diselenide intercalated with nickel (NxTiSe2) are studied systematically in the nickel concentration range x = 0–0.5. In accordance with a model proposed earlier, strong hybridization of the Ni3d/Ti3d states is observed, giving rise to suppression of the magnetic moment because of delocalization of the nickel d electrons. It is shown that the strain caused by the Ni3d/Ti3d hybridization does not change the local coordination of a titanium atom. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The electronic structure of the single-crystalline solid solutions Nb 1-x V x Se 2 has been studied using soft X-ray photoelectron, resonant photoelectron, and absorption spectroscopy. A charge transfer between VSe 2 and NbSe 2 sublattices was observed. This charge transfer makes the octahedral coordination of the Nb atoms by Se atoms preferable as compared to the trigonal-prismatic coordination in undoped NbSe 2. • Nb 0.9 V 0.1 Se 2 and Nb 0.4 V 0.6 Se 2 single crystals were studied using synchrotron radiation spectroscopy. • The NbSe 2 -and VSe 2 -based structural fragments are being formed within both single crystals. • The charge transfer occurs from NbSe 2 to VSe 2. • The observed charge transfer may be responsible for the change of the coordination of the Nb atoms by the Se ones. [ABSTRACT FROM AUTHOR]

A low-temperature layered phase Cu x TiS 2 (0 ≤ x ≤ 0.7) has been prepared. The occupation of both octahedral and tetrahedral sites by the copper atoms in the interlayer gap of the TiS 2 lattice is revealed. The presence of two concentration regions of 0 ≤ x ≤ 0.3 and 0.5 ≤ x ≤ 0.7, which differ in the concentration dependence of the unit cell volume, has been observed. In the first region the unit cell volume increases with x, in the second region it decreases. This difference may be associated with the competition between Cu-Ti and Cu-S covalent centres. The electrical and magnetic properties of the materials are in a good agreement with this assumption. The electronic structure of Cu x TiS 2 in the low copper concentrations region has been studied using X-ray photoelectron, resonant photoelectron and absorption spectroscopy techniques. It was found that, in the low copper concentrations region, the charge transfer from Cu to the conduction band of TiS 2 along with the formation of covalent centres is observed. [ABSTRACT FROM AUTHOR]

The electronic structure of the novel intercalation compound Cu 0.3 ZrTe 2 was analyzed using the X-ray photoelectron spectroscopy, resonant photoelectron spectroscopy and DFT calculations. The resonant photoemission enhancement of the valence band features of Cu 0.3 ZrTe 2 at the Zr 3p→4d and Cu 3p→3d photo absorption thresholds was studied. The tetrahedral coordination of the Cu atoms by the Te atoms was shown to be responsible for the strong chemical bonding of the Cu atoms within the ZrTe 2 lattice through the Cu 3d/Te 5p hybridization. These findings were confirmed by theoretical density of states (DOS) calculations performed for Cu x ZrTe 2 (x = 0.25 and 0.5) with the Cu atoms tetrahedrally and octahedrally coordinated by Te atoms. It was concluded that the substitution of atoms in the Cu x TiSe 2 system with heavier and polarizable ones (Se→Te, Ti→Zr), i.e. an increase in the lattice polarizability, destabilizes the octahedral coordination of the Cu atoms by the Se/Te ones. This limits the stability of the phases characterized by quantum states with a charge density wave and superconductivity. • The crystal structure of CuxZrTe2 is similar to the structure of delafossite-type multiferroics. • The electronic structure of the Cu0.3ZrTe2 single crystal was studied by the XPS, XAS, ResPES methods. • It has been established that the copper chemical bond is formed by selective hybridization of the Cu3d/Te5p states. • It has been established that Cu3d/Te5p hybridization does not lead to the formation of localized states. [ABSTRACT FROM AUTHOR]

[Display omitted] • Composite single crystals of (Fe,Ni) 4 Se 5 and Ti 3 Se 4 on bi-intercalated crystal (Fe,Ni) 0.25 TiSe 2 are grown. • The morphology of these composite crystals has been studied by SEM, AFM and SPEM. • The electronic structure of the inclusions (Fe,Ni) 4 Se 5 in coherent coupling with TiSe 2 was studied. • Mechanism for the formation of such composite crystals has been proposed. • Thermodynamic modeling of the Ti3Se4 and (Fe, Ni) 4Se5 inclusions stability in the composite has been performed. A nanocomposite material consisting of (Fe,Ni) 4 Se 5 and Ti 3 Se 4 nanocrystals coherently bounded with the (Fe,Ni) 0.25 TiSe 2 substrate was obtained during the synthesis of the (Fe, Ni) x TiSe 2 bi-intercalation compound from the mixture of Fe 0.25 TiSe 2 and Ni 0.25 TiSe 2. The morphology of these composite crystals has been studied using optical, scanning electron and atomic force microscopy. The electronic structure of the inclusions was studied using X-ray scanning photoelectron microscopy (SPEM). We have shown that (Fe,Ni) 4 Se 5 and Ti 3 Se 4 inclusions grow simultaneously with (Fe,Ni) x TiSe 2 substrate crystal on its (0 0 1) plane. The lateral growth of the (Fe,Ni) x TiSe 2 crystal is accompanied by the "capturing" of the (Fe,Ni) 4 Se 5 and Ti 3 Se 4 inclusions by the (Fe,Ni) 0.25 TiSe 2 substrate resulting in the formation of the composite crystal. [ABSTRACT FROM AUTHOR]

Influence of the covalence, octahedral distortion and the translation symmetry of the chromium ions in octahedral coordination on the electronic structure for compounds under investigation was clarified. Cr L 2,3 and Ti L 2.3 X-ray absorption spectra (XAS) along with atomic multiplet calculations and resonant Ti 2p-3d and Cr 2p-3d photoelectron spectra of valence band (RXPS) in the intercalated titanium dichalcogenides Cr x TiX 2 (X = Se, Te) and in the substitution compound Ti x Cr 1− x Se 2 show the charge transfer between chromium and titanium sublattices. [ABSTRACT FROM AUTHOR]

A systematic study of the crystal and electronic structure of the intercalation compound Ag x ZrTe 2 in the Ag concentration range of x = 0–0.37 has been performed. It was found that the Ag atoms occupy the sites in the interlayer gap that are tetrahedrally coordinated by the Te atoms. The chemical bond is provided by the Ag 4d/Te 5p hybridization. The comparison of the studied electronic structure with the available data on the electrochemical measurements of Ag x ZrTe 2 in the temperature range of 200–400 °C indicates the formation of covalent centers accompanied by the formation of the half-filled band of Ag 4d/Te 5p hybridized states. The shape of the phase diagram in the region of low Ag concentrations coincides with that observed for Ag x TiTe 2 , in which the stability of the covalent centers is confirmed by the Ag 5s/Ti 3d hybridization. This indicates the universal character of the influence of the localized or extended states of conduction electrons on the phase diagram of intercalation compounds. • The crystal structure of low-temperature and high-temperature synthesized Ag x ZrTe 2 (x = 0–0.37) was studied using XRD. • Single crystals of Ag x ZrTe 2 were studied using electron spectroscopic methods. • The electronic structure and electric resistivity were studied. • The data obtained suggest the Te 5p/Ag 4d hybridization. [ABSTRACT FROM AUTHOR]

The morphology of the heterogeneous Cr x Ti 1-x Se 2 and Cr x Ti 1-x S 2 single crystals has been studied using X-ray scanning photoemission microscopy (SPEM) and angular resolved photoemission spectroscopy (ARPES). A direct method of SPEM provided us the insight into the origin of the blurred ARPES images for Cr 0.78 Ti 0.36 Se 2 single crystal. Using SPEM, we confirmed the formation of the CrSe 2 -based structural fragments inside the Cr x Ti 1-x Se 2 single crystals with x ≥ 0.75. The chemical composition of the forming structural fragments depends on the chalcogen (S, Se) forming the crystal lattice. [Display omitted] • Cr x Ti 1-x Ch 2 (Ch = S, Se) single crystals have been studied using SPEM • Structural fragments with different composition are formed in both Se and S systems • The fragments can be in coherent relation with each other • The fragments in Cr 0.78 Ti 0.36 Se 2 are TiSe 2 -based and CrSe 2 -based solid solutions • The fragments in Cr 0.34 Ti 0.66 S 2 are Cr x Ti 1-x+y S 2 -based solid solutions with different concentration y of superstoichiometric Ti [ABSTRACT FROM AUTHOR]

Abstract: Intercalation of Cu and Mn between the layers of TiSe2 leads to the charge transfer from the doped atom to Ti atoms, electronic states of which form the conduction band of TiSe2. This situation drastically differs from another one being observed during intercalation of other transition metals into TiSe2 that leads to the formation of covalent complexes consisting of intercalated atom and nearest neighborhood of the host lattice. Substitution of Ti by Cr in the host lattice positions does not show both charge transfer nor formation of covalent complexes. [Copyright &y& Elsevier]

Abstract: Scanning tunneling microscopy (STM) and X-ray photoelectron diffraction (XPD) are applied to study the surface of layered dichalcogenide 1T-TiSe2. XPD pattern simulation for the 1T-TiSe2 surface is performed in the approach of electron multiple scattering within the EDAC code: considered are models of structural defects in the 1T-TiSe2 lattice, relaxation contraction (expansion) of surface layers and van der Waals gap, and deviation of the 1T-TiSe2 surface geometry from the basal plane (001). The atomic structure of 1T-TiSe2 surface layers is reconstructed from the XPD pattern on Se(LMM) and Ti2p core level using the photoelectron holography scattering pattern extraction algorithm with maximum entropy method (SPEA-MEM). The results of the 3D reconstruction are in agreement with the XPD pattern simulation data. In both cases, the TiSe2 surface corresponds to 1T polytype; an increase is observed in the parameter a 0 and in the van der Waals gap between two surface slabs. It is assumed that similar structural distortions of the 1T-TiSe2 lattice lead to the formation of an energy gap between the valence band and the conduction band of titanium diselenide, which was observed earlier by photoemission spectroscopy and follows from the theoretical calculations. [Copyright &y& Elsevier]

Abstract: The crystal structure and transport properties of TiS3 whiskers in the plane of layers (ab) have been studied. Maxima of the logarithmic derivative of resistance, dln R/d(1/T), are observed at 17, 60 and 120K both along and across the chains. Strong nonlinearity of the current–voltage characteristics has been revealed in both directions. Nonlinear conductivity along the chains is observed up to T=60K, while in the transverse direction it is observed up to T=130K. The results indicate possible phase transitions of electrons to collective states, probably, charge density waves. [Copyright &y& Elsevier]

Abstract: We synthesize Cr x Ti1−x Se2 (x =0–0.83) and Cr x Ti1−x S2 (x =0.3–0.4) systems and study the structure of these materials on mono- and polycrystalline samples. It appeared that an increase in chromium content leads to inversion of titanium diselenide intercalated with chromium to chromium diselenide intercalated with titanium. The XPS of core levels and valence bands of 1T-Cr x Ti1−x Se2 and Cr x Ti1−x S2 was also investigated and it was shown that in in-layer and inter-layer positions the atoms of chromium and titanium are characterized by a slightly differing oxidation state. Chromium LDOS model calculations were carried out and the results being in agreement with the experimental data show that the Cr 3d density of electronic states of chromium in Ti-positions in the host lattice displays half-metallic properties, while the Cr 3d density of electronic states of intercalated chromium is far from being half-metallic. [ABSTRACT FROM AUTHOR]

[Display omitted] • A layered phase Cr x ZrTe 2 in concentration range 0 < x ≤ 0.3 were synthesized. • Crystal structure was refinement. • The magnetic properties of the materials were measured. • Occupation by Cr atoms of the tetrahedral sites along with octahedral was observed. • Formation of a chemical bond due to the Cr3d/Zr4d–hybridization states can be assumed. New intercalation compounds Cr x ZrTe 2 were synthesized in the Cr concentration range of x = 0–0.3. A thorough study of the crystal and electronic structure has been performed. It was found that there is competition in the distribution of the Cr atoms over the octa- and tetrahedral sites in the van der Waals gap, depending on the Cr content. The ordering of the Cr atoms was found at x ≥ 0.25; at the same time, the lattice symmetry decreases from trigonal P-3m1 to monoclinic F2/m. This ordering stabilizes the octahedral coordination of the Cr atoms by Te atoms. The analysis of the experimental data on the electronic structure and DOS calculations showed that the Cr 3d states are spin-split. However, these Cr states are still overlapped by non-spin-split Zr and Te states. [ABSTRACT FROM AUTHOR]

We report the high-resolution angle-resolved photoelectron spectroscopy (ARPES) experiments and X-ray emission Cr L2,3 and X-ray absorption (XA) spectra of metallic Cr and Ti in Cr1/3TiTe2, 1T-TiTe2, obtained with the use of linearly polarised synchrotron radiation. The emission spectra are studied at the excitation threshold and beyond it. For the case of beyond-the-threshold excitation, additional bands have been detected. Their origin is discussed on the basis of a model of semi-metallic state of the polarons. Our analysis of angle-resolved photoelectron spectra of Cr1/3TiTe2 with those of 1T-TiTe2 indicates a formation of narrow and practically dispersionless band situated approximately 1 eV below the Fermi level. [Copyright &y& Elsevier]

A new laser medium — Yb,Tm:KY(WO[sub 4])[sub 2] — for diode pumped solid state laser applications operating around 1.9 to 2.0 μm has been investigated and the main laser characteristics are presented. Diode pumping at 981 nm and around 805 nm was realised. For 981-nm pumping, the excitation occurs into Yb[sup 3+] ions followed by an energy transfer to Tm[sup 3+]ions. A slope efficiency of 19% was realised. For pumping around 805 nm, the excitation occurs directly into the Tm[sup 3+] ions. Here a maximum slope efficiency of 52%, an optical efficiency of 40%, and output powers of more than 1 W were realised. Using a birefringent quartz plate as an intracavity tuning element, the mnability of the Yb,Tm:KY(WO[sub 4])[sub 2] laser in the spectral range of 1.85-2.0 μm has been demonstrated. The possibility of laser operation in a microchip cavity configuration for this material has also been shown. [ABSTRACT FROM AUTHOR]

Absorption and emission spectra as well as 2F5/2(Yb3+) and 3H4,3F4(Tm3+) excited state relaxation of Yb:Tm-doped potassium yttrium tungstate (KY(WO4)2) crystal were measured. The intensities of the electronic transitions were analyzed from the point of view of further application of this crystal for diode pumped solid-state lasers. The processes of energy transfer between Yb and Tm ions under 980-nm excitation in this medium are discussed. [Copyright &y& Elsevier]

The crystal structure of Fe 0.5 TiSe 2 has been studied in-situ by means of X-ray diffraction technique using synchrotron radiation upon heating in the temperature range 20–1000 °C. It was found that the iron sublattice undergoes a second order transition at a temperature of about 420 °C without affecting the TiSe 2 sublattice. This phase transition has been described using an order parameter, the behavior of which is close to that for a 2D model. It was established that this transition is not related to the first-order transition, associated with the extraction of metallic iron. • The crystal structure of the intercalation compound Fe 0.5 TiSe 2 was studied in the temperature range 25–1000 С. • An order-disorder transition was revealed in the sublattice of the intercalated iron at a temperature of 420 C. • Transition is the transition of the second order and it is described by an order parameter typical for 2D materials. • Order-disorder transition in the Fe sublattice is not associated with the retrograde solubility of Fe in this material [ABSTRACT FROM AUTHOR]

We present a diode-pumped Yb:KYW microchip laser. The passive Q-switched and CW regimes of operation for the Yb:KYW microchip laser have been investigated. An efficiency for CW operation of up to 10% with regard to incident pump has been obtained. Raman self-frequency conversion in the Q-switched regime has been observed. [ABSTRACT FROM AUTHOR]