The negative muon (–) was used as a microscopic probe for the study of the electronic state at the oxygen site in highTc related LaSrCuO materials. Using good single crystals, two types of signals are obtained corresponding to two different oxygen sites: one highly anisotropic, which shows a large (order of 1%) shift under the magnetic field inc-axis direction, the other less anisotropic and with a smaller amplitude (order of 0.2%). These results of –OSR show quit a difference with the result of17O-NMR, where the paramagnetic shift has axial symmetry along the Cu-O bond direction and a magnitude of the order of 0.2% and 0.05%. 相似文献
It is shown that on rapid cooling of the compound Ba2YCu3O7-δ one obtains a highly disordered material in which the perovskite framework is conserved but in which barium and yttrium atoms exhibit a high degree of disorder. This leads to lattice deformations, which can be visualized in the electron microscope. The electron diffraction patterns also reveal the disorder. As-quenched specimens are no longer high Tc superconductors, but the superconducting properties can be recovered by an adequate heat treatment whereby the vacancies become ordered. 相似文献
From XPS core level spectroscopy the average copper charge on the Cu sites in the high temperature superconductor Y1Ba2Cu3O7–x is determined as function of the oxygen vacancy concentrationx. Analysis of these data leads to the suggestion that there are holes on the oxygen sites in the basal plane of the crystal structure. The probability for holes on these oxygen ions is rather constant for 0x0.3 with a value of 0.64 and decreases to zero forx=0.5. The dependence of the superconducting transition temperature on the hole concentration is discussed. An energy level diagram for Cu2+ and Cu3+ in YBa2Cu3O7–x is constructed. 相似文献
An unambiguous determination of the + location in the highTc LaSrCuO superconductor is made through zero-field spin relaxation in the paramagnetic phase and its crystal axis dependence by using single crystalline samples. The temperature dependence of the relaxation rates has a maximum between 80 and 150 K, indicating the existence of the onset of quantum diffusion at low temperature. 相似文献
Electron energy loss spectra of films of amorphous alloys of silicon and carbon were studied. Various compositions of hydrogenated alloys were prepared by glow discharge decomposition of silane and methane mixtures and a control film was prepared by rapid evaporation of crystalline silicon carbide. The near edge structure of the Si Ledge revealed chemical shifts from which bonding information was obtained. The glow discharge specimens showed a variety of local environments for silicon whereas the evaporated specimen showed almost complete heteronuclear bonding. The carbon K edge showed the presence of π1 peaks associated with three fold coordinated carbon in all cases. The amount of this carbon could be reduced in glow discharge films by increasing the growth temperature. 相似文献
199Hg Fourier Transform NMR studies of various solutions of diverse mercury salts in H2O and D2O or in the appropriate protonated and deuterated acids are reported for both Hg2++ and Hg++. In the different solutions investigated the199Hg line positions depend on the concentration of the solution, on the solvents and their isotopic composition and on the temperature of the sample. A ratio of the Larmor frequency of199Hg and of2H in a Hg(NO3)2 solution in dilute DNO3 is given. Using this ratio and the measured chemical shifts, a ratio of the Larmor frequencies of199Hg for infinite dilution relative to2H in pure D2O is given. From this a gI-factor for199Hg is derived and compared with the gI-factor of an optical pumping experiment. The resulting shielding constant is σ* (hydrated199Hg++ versus199Hg atom)=?24.32(5) · 10?4. This yields an atomic reference scale for all measured NMR line shifts of mercury. 相似文献
Scanning probe microscopy has been applied to study various growth stages of YSZ (yttria-stabilized zirconia) buffer layers on silicon and of YBa2Cu3O7–x thin films on YSZ/Si. YSZ buffer layers of 75 nm thickness exhibit a remarkable smooth surface with a rms roughness of about 0.5 nm for a surface area of 5 m×5 m. The subsequent growth of YBa2Cu3O7–x thin films was investigated from nucleation to the formation of growth hills. Screw dislocations were found only in very rare cases. 相似文献
It is shown by means of electron microscopy and electron diffraction that the “structural” vacancies in Ba2YCu3O7−δ undergo an order-disorder transformation accompanied by a change in symmetry from orthorhombic to tetragonal. A superstructure due to the ordering of vacancies was found in certain crystal parts; it leads to doubling of the a0 parameter. It is shown that the ordering of the vacancies is important for the superconducting behaviour. In order to obtain a high Tc supraconductor the final heat treatment is crucial. 相似文献
The electron paramagnetic resonance parameters D, g∥ and g⊥ for V3+ ions in α-Al2O3 crystals are calculated on the basis of the complete diagonalization method and the superposition model. In the calculation, the contributions of the variation of the cation–ligand bond lengths and bond angles are taken into consideration. The calculated results agree well with the experimental data. Our investigation shows that the local structure around the V3+ ions possesses a compressed trigonal distortion above the O2?-triangle and an elongated trigonal distortion in the lower one. 相似文献
We report on the study of the magnetic properties of the low-temperature polymer phases in N2Rb1?xCsxC60 at 110 GHz microwave frequency withx varying between 0 and 1. The magnetic and structural properties of the polymer phase strongly depend on the Cs content and its electronic structure progressively becomes quasi-one-dimensional asx is increased. While the electronic properties of the polymeric Na2RbC60 appear to be close to three-dimensional metal, Na2Rb0.3Cs0.7C60 shows characteristics of quasi-one-dimensional metal where instability in the electronic structure was found as detected by the sudden disappearance of the ESR intensity due to the opening of the gap at the Fermi surface. The observation of an additional resonance line below 15 K, which could be attributed to antiferromagnetic resonance, suggests that the low-temperature polymeric phase in Na2Rb0.3Cs0.7C60 has a well-defined magnetic ground state. 相似文献
Magnetization measurements on the itinerant electron magnet Y(Co1−xAlx)2 up to 350 kOe have clearly revealed metamagnetic transitions in the paramagnetic region (0.07⩽x⩽0.11). The transition is sharp for low x, suggesting itinerant electron metamagnetism to exist in YCo2 at 1 MOe, while it is broadened and disappears upon the onset of ferromagnetism at x∼0.13. 相似文献
Thin films of Y2O3 were deposited on the surface of a zinalco alloy (Zn–22Al–2Cu) in order to modify the surface and increase the corrosion resistance. By means of ion sputtering and surface analysis using Auger electron spectroscopy, in-depth relative elemental intensity profiles were obtained. The growth mechanism of the surface oxides layer is modified by the deposited yttrium oxide film. On samples without film, corrosion progresses mainly at the surface as indicated by the zinc excess, while on samples with film, the growth of the oxides layer occurs at inner points of the film where migrating anions and cations are allowed to find each other. The growth of the corrosion products layer is about nine times smaller in samples with a film of 1600 Å of Y2O3 with respect to samples without a film. Migration of aluminum particles is higher than that of zinc particles, producing a surface highly enriched in aluminum. 相似文献
The interaction of β-cyclodextrin with mercury(II) nitrate has been studied using UV, IR, and 1H NMR spectroscopy, elemental analysis, and quantitative chemical analysis. The optimum conditions for complex formation were
established. The stability constant of the 1:1 inclusion complex of β-cyclodextrin and nitrate was calculated. The formation
of supermolecules of composition C42H70O35·3Hg(NO3)2 in solution and on a silica surface chemically modified with β-cyclodextrin was shown.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 476–481, July–August, 2008. 相似文献
X-ray diffraction patterns and nuclear gamma resonance spectra of La(Fe0.88SixAl0.12 ? x)13 compounds in the paramagnetic state at room temperature have been investigated. It has been found that all samples have a cubic structure of the NaZn13 type, in which Si and Al atoms disorderly substitute for iron in the crystallographic position 96i. An analysis of the Mössbauer spectra using the fitting with doublets with different quadrupole splittings has revealed that the distributions of the aluminum and silicon impurity atoms substituting for iron differ significantly. Aluminum is statistically distributed over nine positions of the 96i type in the generalized coordination sphere of the Fe2 atom, whereas silicon predominantly substitutes for only six of the nine positions. 相似文献
X-ray and uv induced photoelectron spectroscopy have provided information on the various molecular states of nitrogen formed on polycrystalline iron surfaces from dinitrogen and ammonia. At 85 K two distinct states are observed with N2(g) which have N(1s) binding energy values of 405.3 and 400.2 eV. These are in equilibrium with N2(g), are weakly held, and are desorbed on warming to 290 K leaving a nitrogen free surface. The two states are assigned to a molecularly adsorbed and linear species the former characterised by an N(1s) value of 400.2 eV and the latter by 405.3 eV. At 290 K nitrogen is adsorbed with a very low sticking probability (?10?6) giving rise to an N(1s) value of 397.2 eV. This is undoubtedly the dissociatively chemisorbed species. At a nitrogen pressure of l Torr adsorption is “instantaneous” and the N(1s) value is 397 eV. No evidence for the unstable bridged and linear forms of nitrogen is obtained at 290 K although they may well be precursors to the formation of the strongly chemisorbed nitrogen species. Shifts in the N(1s) binding energy induced by subsequent oxygen adsorption are discussed briefly. At 85 K ammonia adsorbs largely in the molecular form with a broad N(1s) peak centred at about 400 eV but on warming to 290 K this splits to give two peaks one at 397 eV and the other at 400 eV. Interaction at 290 K leads to a dominant peak at 397.2 eV and a subidiary one at 400 eV. Helium (1) spectra support the assignment of the 397.2 eV peak to dissociated species (N, NH) and the 400 eV peak to molecular adsorption. The conclusions with N2 and NH3 are substantiated further by comparing the data with results for nitric oxide. The concentration of nitrogen adatom species formed from NO at 290 K and 10?6 Torr is some ten times that formed from N2 at 1 Torr and three times that from NH3 at 10?6 Torr and the same temperature. 相似文献
We present an Auger electron spectroscopy (AES) study of the adsorption of nitric oxide (NO) on a clean Si(100)2 × 1 surface at 300 and 550 K. Accurate measurement reeveal well resolved fine structure at Auger SiL2.3VV transitions at 62 and 83 eV. These peaks can be attributed to SiO and SiN bonds. Furthermore, it is argued that the broadening in the SiLi2.3VV Auger transition at 83 eV at 300 K may be composed of two nearby peaks, which could be attributed to two different kinds of chemical bonding, SiN and SiO. The absence of a peak at 69 eV at room temperature strongly suggests the NO adsorption on a Si(100)2 × 1 surface to be molecular. Dissociation of NO on the Si(100)2 × 1 surface is observed at 550 K. 相似文献
Local electron states in indium-doped lead telluride-based solid solutions exhibit a number of features which separate them from the diversity of impurity states in semiconductors. These features are most pronounced in terahertz photoconductivity. The results of the corresponding experiments performed during the last years and supported by the Russian Foundation for Basic Research are reviewed. 相似文献
The positive muon (+) spin relaxation method under zero external field is applied to probe magnetic ordering in the superconducting phase of a high quality single crystal of La2–xSrxCuO4 (0.10<x<0.15). A series of well characterized crystals with nearly complete flux exclusion were found to exhibit a magnetic ordering with transition temperature depending onx with a peak atx=0.11. Possible explanations are given. 相似文献
The chemical shift of
–O in water, ice and in aqueous hydrogen peroxide (H2O2) was examined using –O resonance. Two distinct signals are obtained in water and ice. Using
+ resonance signal as a standard, the observed shiftsg are –7.0×10–4 (signal A) and –12.1×10–4 (signal B) respectively. The intensity of the two fractions are almost equivalent in water; however, in ice, the intensity of signal B decreases with increase of signal A. After the addition of hydrogen peroxide to the water signal B disappears, A increases, and the total amplitude is increased. 相似文献