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91.
92.
93.
The diffusion of110Ag in Cu2O has been measured by a serial-sectioning technique as a function of temperature (700–1132°C) and oxygen partial pressure (6 × 10?6 ?8 × 10?2 atm). The data are fit to the defect model for Cu2O developed by the authors in the preceding paper. Silver ions have a larger impurity-vacancy binding free energy and/or a larger jump frequency for the singly charged cation vacancies relative to that for the neutral cation vacancies. The activation enthalpies for the diffusion of copper and silver ions in Cu2O are nearly equal, but the absolute value of D1Ag is about three times larger than D1Cu even though the silver ion is 31% larger than the copper ion. 相似文献
94.
Diffusion of 54Mn in Mn1?δO single crystals has been measured by a serial sectioning technique as a function of temperature (1000–1500°C) and deviation from stoichiometry (0.00003 < δ < 0.12). The value of m in the expression varies from about 6 at low Po2 at all temperatures to a value approacing 2 at high Po2 and high temperatures, thus suggesting that diffusion occurs by doubly charged vacancies at low Po2 with increasing contributions from singly charged and neutral vacancies as Po2 (and vacancy concentration) increases. For δ near 0.1, the values of D fall below the values extrapolated from smaller defect concentrations. The isotope effect for cation self-diffusion was measured by simultaneous diffusion of 52Mn and 54Mn in Mn1?δO (0.0004 < δ < 0.116) at 1300 and 1500°C. The measured values of fΔK are independent of temperature within experimental error, and decrease from a value of 0.70 at low defect concentrations to 0.37 for large values of δ. The isotope-effect results suggest that diffusion occurs by single non-interacting vacancies at low defect concentrations; defect-defect interactions become important for δ ? 0.01. The defect-defect interactions may involve essentially individual defects or may result in defect clusters; the similarity between the present isotope-effect results and those for Fe1?δ0 suggests that defect clustering plays a significant role in mass transport in Mn1?δO at large values of δ. 相似文献
95.
96.
Host sensitized energy transfer in CaWO4 doped with Eu3+ and Sm3+ is investigated using pulsed laser time-resolved spectroscopy techniques. The excitation is into the long wavelength tail of the absorption edge and the results indicate that this selectively excites tungstate ions which are located next to activator impurity ions. The subsequent energy transfer is found to be consistent with a single step, nearest neighbor process. Both electric dipole-dipole and exchange interactions can predict strong enough transfer to account for the observed rates. These results are compared to those obtained previously for broad band excitation into the highest energy absorption bands of CaWO4 crystals. 相似文献
97.
S. F. Peterson F. Tera G. H. Morrison 《Journal of Radioanalytical and Nuclear Chemistry》1969,2(1-2):115-125
Isotopic ion exchange for the rapid separation of radioactive mixtures has been further extended through the use of an acetone-water-hydrochloric
acid system. Distribution data were obtained for 27 elements in the range of 15–90% acetone, 0.3N HCl indicating a number of new separations. The approach was used for the separation of several radioisotopes from short
half-life magnesium matrix for activation analysis. The separations were completed in less than 5 minutes.
Research supported by the Advanced Research Projects Agency. 相似文献
98.
W.K. Chen N.L. Peterson L.C. Robinson 《Journal of Physics and Chemistry of Solids》1973,34(4):705-709
Diffusion of 51Cr in NiO single crystals in air has been studied by the tracer-sectioning technique. In the temperature range 1192–1642°C, the diffusion coefficient can be expressed by the Arrhenius expression D=Doexp(-Q/RT), with Do=(8·6±1·2)×10?3 cm2/sec and Q=67·4±1·1 kcal/mole. The use of a high specific-activity tracer and a special configuration for the diffusion anneal prevented the self-dopling effect found by Seltzer and the evaporation of chromium from the sample surface. The present results, in conjunction with published results on nickel self-diffusion in NiO and interdiffusion in the NiO?Cr2O3 system, are used to determine a chromium ion-vacancy binding energy of about 5 kcal/mole in pure NiO. 相似文献
99.
The inelastic scattering of protons, deuterons, τ and α from50Cr has been studied. Spins, parities and transition strengths have been inferred for many states. The 1.89 MeV 4+state is excited by a double-excitation process, but more weakly than expected for a two-phonon state. A weak 5? state is found at 4.37 MeV, and a 5+ state is inferred at 3.792 MeV. 相似文献
100.
D. W. Peterson 《Journal of Optimization Theory and Applications》1974,13(1):56-73
Two types of interpretations of multipliers in both static and dynamic optimization problems are described. It is snown that the Lagrange multipliers encountered in mathematical programming problems and the auxiliary functions arising in Pontryagintype optimal control problems sometimes have highly analogous interpretations as rates of change of the optimal attainable value of an objective function, or in some cases as bounds on average rates of change. 相似文献