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1.
Mössbauer absorption spectra have been measured for Cr3+ doped Al2O3?Fe 2 57 O3 systems for different values of the Cr3+ concentration at room temperature. The cross relaxation between Fe3+ and Cr3+ ions, which destroys the paramagnetic hyperfine structure of Fe57 observed in undoped Al2O3?Fe 2 57 O3, is thoroughly studied. The experimental results suggest a new kind of cross-relaxation process involving three spins, i.e. two Fe3+.ions and one Cr3+. The process, though it is a higher-order one, is highly effective because it is energy-conserving.  相似文献   

2.
B. Amami  M. Addou  F. Millot  A. Sabioni  C. Monty 《Ionics》1999,5(5-6):358-370
Measurements of18O self-diffusion in hematite (Fe2O3) natural single crystals have been carried out as a function of temperature at constant partial pressure aO 2=6.5·10?2 in the temperature range 890 to 1227 °C. The aO 2 dependence of the oxygen self-diffusion coefficient at fixed temperature T=1150 °C has also been deduced in the aO 2 range 4.5·10?4 - 6.5·10?1. The concentration profiles were established by secondary-ion mass spectrometry; several profiles exhibit curvatures or long tails; volume diffusion coefficients were computed from the first part of the profiles using a solution taking into account the evaporation and the exchange at the surface. The results are well described by $$D_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 2.7 \cdot 10^8 a_{O_2 }^{ - 0.26} \exp \left( { - \frac{{542\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ From fitting a grain boundary diffusion solution to the profile tails, the oxygen self-diffusion coefficient in sub-boundaries has been deduced. They are well described by $$D''_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 3.2 \cdot 10^{25} a_{O_2 }^{ - 0.4} \exp \left( { - \frac{{911\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ Experiments performed introducing simultaneously18O and57Fe provided comparative values of the self-diffusion coefficients in volume: iron is slower than oxygen in this system showing that the concentrations of atomic point defects in the iron sublattice are lower than the concentrations of atomic point defects in the oxygen sublattice. The iron self-diffusion values obtained at T>940 °C can be described by $$D_{Fe} \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.2 \cdot 10^{10} a_{O_2 }^{ - 0.56} \exp \left( { - \frac{{578\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ The exponent - 1/4 observed for the oxygen activity dependence of the oxygen self-diffusion in the bulk has been interpreted considering that singly charged oxygen vacancies V O ? are involved in the oxygen diffusion mechanism. Oxygen activity dependence of iron self-diffusion is not known accurately but the best agreement with the point defect population model is obtained considering that iron self-diffusion occurs both via neutral interstitals Fe x i and charged ones.  相似文献   

3.
The mass distribution of emitted V n O m ? and Nb n O m ? clusters and their unimolecular decay by all stoichiometrically possible fragmentation channels, which takes place under the sputtering of niobium and vanadium surfaces and blowing by oxygen, are studied. It is shown that the formation, excitation, and unimolecular fragmentation of V n O m ? and Nb n O m ? clusters can be described by a statistical recombination mechanism. Clusters are formed over the target surfaces as a result of binary collisions of independently sputtered ions, atoms, and molecules.  相似文献   

4.
5.
The mass distributions and fragmentation routes of Nb n O m + and V n N m + clusters sputtered from an metal surfaces with Xe+ ions under O2 pressure of P = 4?5 × 10?3 Pa in a bombardment chamber are studied by means of secondary ion mass spectrometry. The spectra of kinetic energy release distribution (KERD) are measured for the most probable routes of the fragmentation of Nb n O m + and V n N m + and clusters, on the basis of which the activation energies of the decomposition (dissociation) of Nb n O m + and V n N m + clusters are determined within the model of evaporative ensemble and the theory of monomolecular reactions. The results show the closeness of the numerical values of dissociation energies derived using both models.  相似文献   

6.
The precursor-derived nanostructured solid solutions Zn0.95 M 0.05O (M = Co, Ni, Cu) with tubular aggregates have been investigated using optical absorption spectroscopy and electron paramagnetic resonance. The dependences of the concentration of intrinsic defects V o + and the effective band gap on the dopant type have been determined. It has been shown using the oxidation reaction of hydroquinone dissolved in water as an example that an increase in the photocatalytic activity in the series ZnO → Zn0.95Ni0.05O → Zn0.95Co0.05O Zn0.95Cu0.05O in the ultraviolet and visible spectral regions correlates with a decrease in the band gap and with an increase in the concentration of oxygen vacancies V O + .  相似文献   

7.
Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 gs + →2 γ + ),B(E2; 0 gs + →2 β + ),B(E2; 2 gs + →0 β + ) andB(E2; 0 gs + →3 oct ? ) in150Nd,152, 154Sm,154, 158Gd,164Dy and166Er. TheB(Eλ; 0 gs + I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 γ + -states, 0.8 single-particle units for the 2 β + -states and from 14.1 to 21.7 single-particle units for the 3?-states.  相似文献   

8.
The intensity of molecular ions XnO m ± in secondary ion mass spectra originating from surface oxidation by primary oxygen ions is reduced by a residual oxygen pressure. This fact can be used to increase sensibility.  相似文献   

9.
The energy spectra of Si n O m ? clusters sputtered from Si targets by Xe+ ions with O2 pumping onto a bombarded surface, as well as by O 2 + ions, are studied. It is shown that the form of the Si n O 2n+1 ? energy distributions does not depend on the experimental conditions. Significant differences in the energy spectra of O and Si monomers as compared to Si n O 2n+1 ? clusters are revealed. The mentioned features of the energy distribution of Si n O m ? clusters are explained within the framework of the statistical recombination mechanism of their formation in combinatorial synthesis processes.  相似文献   

10.
Sol–gel-derived SrTa2O6 thin films were fabricated at a low temperature of 500 °C. To improve their leakage current properties, additional UV/O3-assisted annealing was performed from room temperature to 290 °C. UV/O3 treatment at 290 °C gave a very low leakage current that was six orders of magnitude lower than that of an untreated thin film. During UV/O3-assisted annealing, Si and Ti ions diffused from the substrates into the SrTa2O6 thin films and occupied the Ta5+ sites, subsequently generating Si? and Ti?. At a heating temperature of 290 °C, large amounts of Ti ions diffused throughout the SrTa2O6 thin film. These Ti ions contributed to the generation of inactive combinations of $(\mathrm{Si}^{-}\mbox{--}\mathrm{V}_{\mathrm{o}}^{+})^{+}\mbox{--}\mathrm{Ti}^{-}$ and $(\mathrm{Ti}^{-}\mbox{--}\mathrm{V}_{\mathrm{o}}^{+})^{+}\mbox{--}\mathrm{Ti}^{-}$ , which greatly reduced oxygen vacancies (Vo). Thus, the leakage current was significantly reduced.  相似文献   

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