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1.
The XYZ model describes the interaction between nuclear probes and an electric field gradient that fluctuates among three orthogonal
directions. The model presents a means to calculate the perturbation function that represents spectra obtained using perturbed
angular correlation spectroscopy. Three analytic approximations of the perturbation function have been developed previously,
and they are evaluated in the present paper in the context of Cd jumping among In-lattice sites in In3La. 相似文献
2.
We report on a procedure developed to create stochastic models of hyperfine interactions for complex diffusion mechanisms and demonstrate its application to simulate perturbed angular correlation spectra for the divacancy and 6-jump cycle diffusion mechanisms in L12-structured compounds. 相似文献
3.
Evenson William E. Lu Jun Winz Michele W. Gardner John A. Zacate Matthew O. Lee Teresa Mommer Niels 《Hyperfine Interactions》1999,120(1-8):427-431
In order to explain PAC data for tetragonal zirconia at temperatures between 900 and 1300oC, we have developed a four-state
stochastic model. The model simulates vacancies which trap and detrap at a PAC probe nucleus. While trapped, the vacancies
hop around the probe in equivalent sites. The four states in this Winkler–Gerdau stochastic theory are three trapped states
with equivalent electric field gradients (EFGs) of different orientations and a detrapped state with a weaker EFG whose axis
of symmetry is oriented along the diagonal between the three trapped EFGs. There are three hopping rates in this model: w,
the rate a trapped vacancy hops around the probe, wD, the detrapping rate, and wt, the trapping rate. We report results of calculations for values of these hopping rates implied by our tetragonal zirconia
data, and we report heuristic fitting functions which summarize the computer results and can be used to fit data efficiently
for a wide range of parameters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The site occupation of indium solutes in Ni2Al3-type compounds was determined using perturbed angular correlation of gamma rays. Measurements were made for compositions
on both sides of the stoichiometric composition. Sites were identified through their quadrupole interactions. For transition-metal
(TM) rich aluminides and galliumides, indium solutes occupy only one of two inequivalent trivalent-metal sites (Al or Ga).
For TM-poor aluminides, indium solutes tend to locate at noncrystallographic sites such as in grain boundaries. For TM-poor
galliumides, the solutes occupy nickel sites while close to the stoichiometric composition they also occupy sites on an empty
Ni-sublattice. Composition dependences of site preference for indium solutes in Pt2Al3 and Ni2Ga3 are examined in terms of a recently developed thermodynamic model.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
5.
6.
A thermodynamic model for site preferences of solute atoms in ordered binary phases is applied in this paper for substitutional
and interstitial sites of the Cu3Au, or L12, structure. Site preferences are found to depend on formation energies of combinations of elementary point defects and on
energies for transfer of solutes among different sites. The composition dependence in compounds having a wide phase field
is examined in detail. A phenomenology of site preference behavior is outlined for regular lattice sites as well as for non-lattice
sites such as grain boundaries.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
7.
Xiaojun Zeng Wenhao Yan Samson B. Zacate Aijie Cai Yufei Wang Dongqi Yang Kundi Yang Wei Liu 《Angewandte Chemie (International ed. in English)》2020,59(38):16398-16403
The difluoromethyl group (CF2H) is considered to be a lipophilic and metabolically stable bioisostere of an amino (NH2) group. Therefore, methods that can rapidly convert an NH2 group into a CF2H group would be of great value to medicinal chemistry. We report herein an efficient Cu‐catalyzed approach for the conversion of alkyl pyridinium salts, which can be readily synthesized from the corresponding alkyl amines, to their alkyl difluoromethane analogues. This method tolerates a broad range of functional groups and can be applied to the late‐stage modification of complex amino‐containing pharmaceuticals. 相似文献
8.
Zacate Matthew O. Walsh Bonner C. Peng Luke S.-J. Collins Gary S. 《Hyperfine Interactions》2001,136(3-8):653-658
Fractions of indium solutes in each phase of a mixture of two binary phases were measured using perturbed angular correlation
of gamma rays. Measurements of phase fractions were made on Pd3Ga7–PdGa, PdGa–Pd5Ga3, and FeAl2–FeAl mixtures as a function of composition. The phase fractions were analyzed using a thermodynamic model that takes into
account differences between energies of solute atoms in the two phases. From the model, segregation coefficients were obtained
for the systems studied. Also, earlier measurements on Ni2Al3–NiAl were reanalyzed. Large differences are found among the segregation coefficients.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
9.
Gardner J.A. Lee T. Mommer N. Karapetrova E. Zacate M.O. Platzer R. Evenson W.E. Sommers J.A. 《Hyperfine Interactions》1999,120(1-8):87-95
For several years this research group has been using 111In/Cd TDPAC to study oxygen vacancies in pure and lightly doped zirconia powders at temperatures up to 1400°C. This paper
includes a brief survey of important results from those studies and some recent results. In particular, our new measurement
showing negligible relaxation due to vacancy hopping above 600°C provides a major breakthrough in our ability to analyze PAC
data and to determine accurately hopping and trapping rates and enthalpies for vacancies in tetragonal zirconia.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Egbert R. Nieuwenhuis Aurélie Favrot Li Kang Matthew O. Zacate Gary S. Collins 《Hyperfine Interactions》2004,158(1-4):305-308
Nuclear quadrupole interactions of 111Cd probes in In2La and CeIn2 were measured using perturbed angular correlation of gamma rays (PAC). Near room temperature, a single non-axially symmetric
quadrupole interaction was observed in each compound, with ω
0 = eQV
zz
/ℏ = 78.8(2) Mrad/s and η = 0.312(1) for In2La at 11°C and ω
0 = 80(1) Mrad/s and η = 0.29(2) for CeIn2 at 34°C. The observed non-axial symmetry is consistent with the reported CeCu2 structure of the phases. The non-axially symmetric interactions were replaced completely by axially symmetric interactions
(η = 0) at 524°C, with ω
0 = 101.0(1) Mrad/s in In2La and ω
0 = 96.9(4) Mrad/s in CeIn2. The change in symmetry is attributed to a polymorphic phase transformation. Based on symmetry information from the quadrupole
interaction and on chemical arguments, it is proposed that high-temperature phases of In2La and CeIn2 both have the AlB2 (C32) structure. 相似文献