A theoretical study of photoelectron spectra of NbO2, MoO2 and RuO2 by cluster models

DV-Xα calculations have been applied to various small clusters of rutile-family dioxides (NbO₂, MoO₂ RuO₂). It appears that by taking into consideration the potential due to the atomic charges, the density, the ionization cross sections of the energy levels, and by summing the density of states (DOS) of the two different clusters representing surface structures, computations on even small clusters provide information which compares well with the experimental XPS spectra.     

Electronic structures of MRhO2, MRh2O4, RhMO4 and Rh2MO6 on the basis of X-ray spectroscopy and ESCA data

X-ray O Kα, Rh Mγ and a series of M Lα emission spectra, ESCA spectra of the valence and inner levels, and O K and Rh M_III quantum-yield spectra for X-ray photoemission of the rhodium double oxides MRhO₂ (M = Li, Na, K), MRh₂ O₄ (M = Be, Mg, Ca, Sr, Ba, Co, Ni, Cu, Zn, Cd, Pb), RhMO₄ (M = V, Nb, Ta) and Rh₂MO₆ (M = Mo, W) have been measured and the dependence of electronic structure on the metal M analysed. For all compounds the inner part of the valence band corresponds to O 2p_σ + O 2p_π + Rh 4d states, while the outer part corresponds to Rh 4d. The valence band is separated from the conduction band by a narrow gap of width less than 1 eV. The first empty band, near the bottom of the conduction band, is formed by Rh 4d states, followed by a band due to vacant O 2p states.     

On the valence states of cerium in CeO2

The absorption spectra below the 4d threshold of cerium in Ce metal, CeF₃ and CeO₂ compounds were measured by using a CDM (Constant Deviation Monochromator) at the Photon Factory, KEK. The difference in structure between these spectra is discussed. The structure appeared in CeO₂ were considered to be due to the tetravalent configuration of cerium (Ce⁴⁺) in the ground state.     

Synthesis and characterization of spherical core-shell particles SiO2@AgEu(MoO4)2

Submicron spherical SiO₂ particles have been coated with AgEu(MoO₄)₂ phosphor layers by a sol-gel process, followed by surface reaction at high temperature, to get core/shell structured SiO₂@AgEu(MoO₄)₂ particles. X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the resulted core-shell phosphors. The luminescent properties of the core-shell structured phosphors have also been measured at room temperature, and their photoluminescence (PL) spectra are similar to the pure AgEu(MoO₄)₂ phosphor prepared by the same sol-gel method exhibiting red emission.     

The optical properties of Dy-doped NaY(MoO4)2 crystal

The Dy³⁺-doped NaY(MoO₄)₂ single crystals were grown successfully by the Czochralski technique. The main spectroscopic properties (absorption, luminescence, decay curve) of Dy³⁺-doped NaY(MoO₄)₂ have been determined for both the σ and π polarizations. By using the Judd-Ofelt theory, the measured room temperature absorption spectra were applied to determine the intensity parameters, spontaneous transition probabilities, branching ratios, and radiative lifetimes of Dy³⁺ transitions. The results show that the Dy³⁺-doped NaY(MoO₄)₂ crystal may realize the yellow laser operation.     

Raman scattering and optical absorption studies of an orbital ordered Ca2RuO4

We have reported the Raman scattering and infrared absorption results on a t_2g orbital ordered Ca₂RuO₄. At 10 K, a strong and clear peak was observed in Raman scattering near 1360 cm⁻¹ with x′x′ geometry. In contrast to optic phonon modes, the peak does not show any frequency shift but rapidly decreases with increasing temperature. In addition, the peak is not observed in infrared absorption measurement. By comparing the previous Raman scattering results for several transition metal oxides, we have discussed the possible origins and ambiguities of the intriguing peak in Ca₂RuO₄.     

ESR- and magnetic susceptibility measurements on the potassium molybdenum bronzes

Magnetic and transport properties of the transition metal bronzes are determined by the extent of delocalization of the transition metal 4d-electrons. We report on ESR investigations of single crystals of the “red” potassium molybdenum bronze K_0.33MoO₃ and of the “blue” potassium molybdenum bronze K_0.30MoO₃. ESR spectra due to unpairedd-electrons are observed at both compounds. Analyzing the hyperfine structure we find that thed ¹-electrons are delocalized over six molybdenum lattice sites in semiconducting K_0.33MoO₃. The same K_0.33MoO₃ crystals show another spectrum which is caused by pairs of exchange coupledd-electrons. Our results are compared with those from magnetic susceptibility measurements and are discussed in connection with the crystal structure of K_0.33MoO₃ and K_0.30MoO₃.     

Hyperfine interaction of d-electrons in the amorphous semiconductors MoO3-TeO2 and MoO3-P2O5

ESR spectra of the amorphous semiconducting systems MoO₃-TeO₂ and MoO₃-P₂O₅ are presented. The occurence of a hyperfine splitting is confirmed by numerical simulations of the observed spectra and by enriching with the isotope Mo⁹⁵. The isotropic hyperfine field at the molybdenum nucleus amounts to (113±10) kG at high MoO₃ concentration. This value is compared with results of measurements on crystalline MoO₃.     

Growth, thermal and spectroscopic characterizations of BaNd2(MoO4)4 crystal

A new crystal, BaNd₂(MoO₄)₄, has been grown from the flux melt based on Li₂Mo₃O₁₀ by a spontaneous nucleation method. The phase structure of the obtained crystals was determined by X-ray powder diffraction. The result shows that the as-grown crystals are well crystallized and indexed in a monoclinic crystal system with space group B2/b. The specific heat of BaNd₂(MoO₄)₄ crystal at 20 °C is 0.485 J/g K. Absorption and fluorescence spectra were also measured at room temperature. There are several strong and broad absorption peaks from 200 to 1200 nm and three emission transition bands located at 890, 1060, and 1334 nm are detected.     

Raman spectra of CrO2 and MoO2 single Crystals

The Raman spectra of single crystals of CrO₂ and MoO₂ have been studied from 77°K to 500°K for a comparison with the heavily damped phonon features in metallic VO₂. The spectrum of MoO₂ is very similar to that of monoclinic VO₂ whereas CrO₂ exhibits phonon spectra similar to rutile with no appreciable change at the ferromagnetic c curie temperature. The results are discussed with respect to the various models proposed for the semiconductor-to-metal transition in VO₂.     

MoO3/Al2O3催化剂中Mo分散的正电子研究

用浸渍法制备了一系列不同Mo含量的MoO₃/Al₂O₃催化剂.测量了这些样品的正电子湮没寿命谱(PALS)与符合多普勒展宽(CDB)谱,以研究其孔洞结构以及Mo分散.正电子寿命测量结果表明,Al₂O₃载体中存在两种不同尺寸的孔洞.掺入MoO₃之后,Mo原子主要进入Al₂O₃的大孔中,使孔洞体积减小.符合多普勒展宽谱结果表明,当MoO 关键词： 3/Al₂O₃催化剂')" href="#">MoO₃/Al₂O₃催化剂 正电子湮没寿命谱 符合多普勒展宽 Mo 分散     

Tunneling conductance in ferromagnet/Sr2RuO4 junction: Detection of the d-vector direction

When a spin-triplet superconductor is attached to a ferromagnet, the tunneling conductance depends not only on the degree of the spin polarization but also sensitively on the relative angles between the magnetic moment in ferromagnet and the d-vector in spin-triplet superconductor. We study theoretically the tunneling conductance in ferromagnet/triplet superconductors assuming three nodal unitary gap functions, which are promising candidates for the pairing symmetry of Sr₂RuO₄. Our results suggest that the d-vector direction in Sr₂RuO₄ may be detected by performing angular dependent tunneling spectroscopy in this hybrid structure. We also show that these three gap functions can be distinguished by their distinctive conductance spectra.     

Esca studies of Ga,As, GaAs,Ga2O3, As2O3 and As2O5

The binding energies of Ga 3d, As 3d, Ga L₃M₄,₅M₄,₅ and O 1s in Ga, As, GaAs, Ga₂O₃, As₂O₃ and As₂O₅ are reevaluated by means of ESCA. The calibration lines of the C 1s and the Au 4f_{$\text{7}\text{2}$} gave different binding energies for the compound materials. In order to determine the absolute binding energies, the chemical shifts in Auger and photoelectron lines from a layered structure composed of thin layer oxide and substrate of a defined material were used. An energy calibration curve, E(Ga 3d) vs. ΔE(GA LMM - Ga 3d), was found to be useful for determination of binding energies in the material which contains gallium. In the case of the GaAs sample, both the chemical etching and the ion bombardment effects on the chemical structure of the GaAs surface are also discussed.     

Magnetic properties of large-area one-dimensional WO2 and MoO2 nanorods

Large-area one-dimensional (1D) monoclinic WO₂ and MoO₂ nanorods in the space group P2₁/c were synthesized by reactive thermal evaporation. The as-synthesized 1D WO₂ and MoO₂ nanorods become soft magnetic materials at 10 K, implying that structural or magnetic transitions occur. There are large differences in saturation magnetization, the coercive field, and remanence between the 1D WO₂ and MoO₂ nanorods, although both 1D nanorods have a similar shape.     

Electronic structure of ErH2

A band structure study reveals that in contrast to the pure rare earth metal, the Fermi level of the dihydride falls near the bottom of the 5d band, in a region of low density of states; consequences on Fermi surface geometry, magnetic properties and resistivity are suggested. Below the metal d states lie two overlapping metal-hydrogen bands, in agreement with Weaver's photoemission data and Switendick's result on YH₂.     

Raman spectra of TiO2-II,TiO2-III,SnO2, and GeO2 at high pressure

Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO₂, GeO₂ and SnO₂ are described. At room temperature, the TiO₂ II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO₂-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO₂ phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO₂ are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO₂, where p-electron bonding is involved, is much less Enharmonic.     

Theoretical investigation of optical spectra and covalent effect of Cr in Y2Ti2O7 and Y2Sn2O7

In this work, the complete matrix of optical spectral levels in trigonal symmetry of 3d² (3d⁸) ions are established on basis of strong field coupling mechanism by using two spin–orbit coupling parameters model. The contribution of the spin–orbit coupling of ligand to the optical spectra has been included in these formulas. As an application, the optical spectra of Cr⁴⁺ in Y₂Ti₂O₇ and Y₂Sn₂O₇ have been studied by the complete diagonalization (energy matrix) method. The covalent effect has been studied and the difficulty about Dq parameter in explanation of optical spectra of Cr-doped Y₂Ti₂O₇ and Y₂Sn₂O₇ is removed. The theoretical results are in good agreement with observed data.     

Structural studies of rhodium doped Sr2RuO4

The influence of Rh doping on the structure of Sr₂RuO₄ has been investigated using neutron powder diffraction methods. The metallic Ru rich compounds adopt a regular K₂NiF₄-type structure, space group I4/mmm, with Ru-O-Ru bond angles of 180°. The structures of the nonmetallic Rh rich compounds crystallise in space group I4/acd and are characterised by tilting of the MO₆ octahedra reducing the Ru-O-Ru angle to about 160°. Irrespective of Rh content the MO₆ polyhedra are not regular octahedra but are elongated along the c direction. The temperature dependence of the structure of Sr₂Ru_0.9Rh_0.1O₄ was investigated and revealed this elongation to be weakly temperature dependent.     

Absolute sense of piezoelectric coefficients in the chalcopyrites ZnGeP2 and AgGaS2

The absolute orientation of single crystals of ZnGeP₂ and AgGaS₂ on which the relative sense of the d₁₄ and d₃₆ piezoelectric coefficients had been measured, was determined by the X-ray absorption edge method. Both coefficients were thereby found to be positive, corresponding in the point charge model to positive charge associated with the metal and negative charge with the nonmetal atoms, in contrast with the negative d_33′ reported in GaP.     

On the properties of the 1s-forms of TaSe2 and TaS2

The 1s-forms of TaSe₂ and TaS₂ with octahedral coordination of the metal are diamagnetic; 1s-TaS₂ is a semiconductor at low temperature. The diamagnetism is explained by taking account of spin-orbit coupling which leads to a ground state with zero magnetic moment (g = 0). This spin-orbit coupling stabilizes the d¹ configuration of the metal with respect to d² + d⁰. Thus, it can be understood that 1s−TaS₂ is semiconducting, while isostructural VSe₂ is metallic. Similarly, BaTaS₂ and BaTaSe₃ are semiconductors, but BaVS₃ is metallic.