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1.
The vibration frequencies of unstable ferroelectric and antiferrodistortion modes and the dependences of the energy on the
ion displacement amplitude have been calculated within the generalized Gordon-Kim model for distortions along eigenvectors
of these modes in the mixed compounds Sr1 − x
A
x
Ti1 − x
/4□
x/4O3 and Sr1 − y
A
2y
/3□
y/3TiO3 (A = Sc3+, In3+, La3+, Bi3+; □ is the vacancy). To compensate an excess positive charge, vacancies are introduced into the Ti4+ or Sr2+ site. Calculations have been performed in the “daverage” crystal approximation for impurity concentrations of 0.25 and 0.50.
To this end, a set of 40 atomic superlattices with various orderings of heterovalent ions Sr2+ and impurity A
3+ has been considered. It has been found that each impurity type, independently of charge balance, induces ferroelectric instabilities
in doped compounds. In the case of doping with In3+ and La3+ for concentration x = 0.25, the possibility of rotating the polarization vector has been shown. 相似文献
2.
The local crystal structure of Gd3+ and Eu2+ cubic impurity centers in cadmium fluoride is calculated within the shell model in the pair potential approximation. The local compressibility of the cationic and anionic sublattices of the host lattice is determined in the vicinity of the Gd3+ (Eu2+) impurity ion. 相似文献
3.
A two-photon impurity absorption coefficient of the “quantum dot — D(−)-center” complexes synthesized in a transparent dielectric matrix is calculated within the model of zero-radius potential.
The evolution of spectral dependence of the absorption coefficient of the nanoheterostructure based on semiconductor CdS
x
Se
1−x
glasses is studied versus the average quantum-dot radius. It is shown that the contribution of the two-photon impurity absorption
to the exited two-photon luminescence is fairly significant at a reasonable quantum-dot concentration.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–50, July, 2005. 相似文献
4.
V. A. Chernyshev A. V. Abrosimov T. S. Koroleva A. N. Cherepanov 《Physics of the Solid State》2005,47(8):1476-1478
The local structure of Zn2+ impurity centers in a uranium-activated lithium fluoride crystal LiF: U,Zn is calculated in the framework of the shell model in the pair potential approximation. 相似文献
5.
A. I. Oreshkin V. N. Mantsevich N. S. Maslova D. A. Muzychenko S. I. Oreshkin V. I. Panov S. V. Savinov P. I. Arseev 《JETP Letters》2007,85(1):40-45
The results of UHV STM investigations of tunneling current noise spectra in the vicinity of individual impurity atoms on the
InAs(110) surface are reported. It was found that the power law exponent of 1/f
α noise depends on the presence of an impurity atom in the tunneling junction area. This is consistent with the proposed theoretical
model considering tunneling current through a two-state impurity complex model system taking into account many-particle interaction.
The text was submitted by the authors in English. 相似文献
6.
The electron paramagnetic resonance (EPR) parameters (g-factors g
‖, g
⊥ and zero-field splitting D) of two tetragonal 3d3 impurity centers M3d-VMg and M3d-Li+ (where M3d = Cr3+ or Mn4+, VMg is the Mg2+ vacancy) in M3d-doped MgO crystals are calculated from the high-order perturbation formulas including both the crystal-field (CF) and the
charge-transfer (CT) mechanisms for 3d3 ions in the tetragonal symmetry. The calculated results are in reasonable agreement with the experimental values. From the
calculations, it can be found that the relative importance of the CT mechanism for EPR parameters increases with increasing
valence state of the 3d3 ion. So, for the high-valence 3d
n
ions in crystals, a reasonable explanation of EPR parameters should take into account both CF and CT mechanisms. The defect
structures (characterized by the displacement ΔR of O2− in the intervening M3d and VMg or Li+ at the Mg2+ site) for these tetragonal impurity centers are obtained from the calculations. The results are consistent with the expectations
based on the electrostatic interactions. 相似文献
7.
A. S. Zhuravlev L. V. Kulik V. E. Bisti I. K. Drozdov V. E. Kirpichev I. V. Kukushkin 《JETP Letters》2011,92(9):607-612
The excitation spectrum of a two-dimensional electron system in high-quality AlGaAs/GaAs quantum wells has been studied by
Raman scattering. New Raman lines due to the excitation of interface D
− complexes in which two electrons localized in a quantum well are coupled to a charged impurity at the quantum well interface
have been identified. The ground state of the interface D
− complexes has been found to change in the transverse magnetic field from spin-singlet to spin-triplet, similar to a change
in the ground state of the system of two electrons localized in a harmonic potential. 相似文献
8.
E. I. Baibekov 《Physics of the Solid State》2010,52(2):246-253
The technique of calculation of the n-phonon transition rates between electronic sublevels of impurity rare earth ions in dielectric crystals is developed in the
case when n>2. The n-phonon transition probabilities are calculated according to the 1st and 2nd orders of perturbation theory. The Hamiltonian
of the electron-phonon interaction is constructed in the framework of the exchange charge model and developed as series in
relative displacements of the rare earth ion and ligands. The contribution of the lattice anharmonicity on the probabilities
of n-phonon transitions is taken into account. On the basis of the developed technique, the nonradiative relaxation rates of 4
G
7/2 multiplet of Nd3+ ions in LiYF4:Nd3+crystal and 3P1 multiplet of Pr3+ ions in CsCdBr3:Pr3+ crystal were computed. The results of our calculations show that the 2nd order terms in the expressions for the probabilities
studied here are comparable with, and in some cases prevail over the 1st order terms. An account of lattice anharmonicity
in case of LiYF4:Nd3+ crystal substantially modifies the corresponding multiphonon relaxation rates. The calculated nonradiative relaxation rates
for both crystals agree well with the experimental data. 相似文献
9.
10.
N. Türkan 《Physics of Atomic Nuclei》2007,70(9):1477-1484
We determined the most appropriate Hamiltonian that is needed for calculations of nuclei in the A ≅ 130 region from the viewpoint of the interacting boson model (IBM). Using the best-fitted values of parameters in the Hamiltonian,
we have calculated energy levels and B(E2) values for a number of transitions in some doubly even Nd nuclei of 128 ⩽ N ⩽ 140. The results were compared with the previous experimental and theoretical data, and it is observed that they are in
good agreement. The calculations have been extended to Nd isotopes for which some B(E2) values are still not known.
The text was submitted by the author in English. 相似文献
11.
12.
In this study, production rates of 125,123Xe and 133,131,129,128Ba medical isotopes produced by 127I(p, 3n)125Xe, 127I(p, 5n)123Xe, 133Cs(p, n)133mg
Ba, 133Cs(p, 3n)131mg
Ba, 133Cs(p, 5n)129Ba, and 133Cs(p, 6n)128Ba reactions have been investigated up to 100 MeV incident proton energy. The preequilibrium calculations involve the hybrid
model, the geometry-dependent hybrid model and the cascade exciton model. The calculated results are compared with the experimental
data taken from the literature. 相似文献
13.
S. Kumari S. N. Chatterjee L. K. Jha B. N. Roy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(2):355-363
H+ impact single and He2+ impact single and double electron
capture cross sections of magnesium atoms have been calculated in the
modified binary encounter approximation (BEA). The accurate expressions of
ion impact sDE\sigma _{\Delta {E}} (cross section for energy transfer
DE\Delta E) and Hartree-Fock momentum distributions of the target
electrons have been used throughout the calculations. On the basis of the
present work it is concluded that inner shell captures by H+ and
He2+ ions incident on magnesium atoms contribute partly to single
electron capture and partly to transfer ionization cross sections. The
calculated He2+ impact double electron capture cross sections of
magnesium are in reasonably good agreement with the experimental
observations. This indicates the success of the present theoretical approach
in study of charge transfer cross sections of atoms as indirect mechanisms do
not interfere with double electron capture processes in this case. 相似文献
14.
The excitation functions for both the evaporation residue and fission have been calculated for 10B + 209Bi and 11B + 209Bi reactions forming compound systems 219, 220Ra* , using the dynamical cluster-decay model (DCM) with effects of deformations and orientations of the nuclei included in it.
In addition to this, the excitation functions for complete fusion (CF) are obtained by summing the fission cross-sections,
neutron evaporation and charged particle evaporation residue cross-sections produced through the axn\ensuremath \alpha xn and pxn\ensuremath pxn (x = 2, 3, 4) emission channels for the 219Ra system at various incident centre-of-mass energies. Experimentally the CF cross-sections are suppressed and the observed
suppression is attributed to the low binding energy of 10, 11B which breaks up into charged fragments. The reported complete fusion (CF) and incomplete fusion (ICF) excitation functions
for the 219Ra system are found to be nicely fitted by the calculations performed in the framework of DCM, without invoking a significant
contribution from quasi-fission. Although DCM has been applied for a number of compound nucleus decay studies in the recent
past, the same is being used here in reference to ICF and subsequent decay processes along with the CF process. Interestingly
the main contribution to complete fusion cross-section comes from the fission cross-section at higher incident energies, which
in DCM is found to consist of an asymmetric fission window, shown to arise due to the deformation and orientation effects
of formation and decay fragments. 相似文献
15.
In this study, the excitation functions for the reactions 203Tl(p, n)203Pb, 205Tl(p, 3n)203Pb, 203Tl(p, 2n)202Pb, 205Tl(p, 4n)202Pb, 203Tl(p, 3n)201Pb, 205Tl(p, 5n)201Pb, 203Tl(p, 4n)200Pb and 205Tl(p, 6n)200Pb have been calculated using pre-equilibrium and equilibrium reaction mechanisms. Calculated results based on hybrid model,
geometry-dependent hybrid model and cascade-exciton model have been compared with the experimental data.
相似文献
16.
Observables of the elastic and inelastic scattering of 800- and 250-MeV protons on 20Ne and 24Mg nuclei were calculated on the basis of the theory of multiple diffractive scattering and the dispersive α-cluster model. The 20Ne and 24Mg nuclei were assumed to consist of a core (16O nucleus) and additional alpha-particle clusters, which could be situated with the highest probability both in the vicinity
of the center of mass of the core and outside the core. The multiparticle densities of these nuclei and single-particle nucleon-distribution
densities as obtained from the dispersive α-cluster model were used in the calculations. The differential cross sections and polarizations for elastic and inelastic
p
20Ne and p
24Mg scattering at the energy of 800 MeV are in better agreement with experimental data than the analogous calculations at the
energy of 250 MeV. The spin-rotation functions calculated in the singleparticle approximation for elastic p
20Ne and p
24Mg scattering at these two energy values differ qualitatively from their counterparts calculated on the basis of the dispersive
α-cluster model. 相似文献
17.
I. M. Suslov 《Journal of Experimental and Theoretical Physics》2011,112(2):274-287
It has been previously shown that calculation of the renormalization group (RG) functions of scalar ϕ4 theory reduces to analysis of thermodynamic properties of the Ising model. Using high-temperature expansions for the latter,
RG functions of the four-dimensional theory can be calculated for arbitrary coupling constant g with an accuracy of 10−4 for the Gell-Mann-Low function β(g) and with an accuracy of 10−3–10−2 for anomalous dimensions. The expansions of the renormalization group functions up to the 13th order in g
−1/2 have been obtained. 相似文献
18.
A. S. Nizamutdinov V. V. Semashko A. K. Naumov R. Yu. Abdulsabirov S. L. Korableva M. A. Marisov 《Physics of the Solid State》2005,47(8):1457-1459
The photochemical properties of CaF2 crystals activated by Ce3+ and Yb3+ ions are studied. A model of the photodynamic processes induced by pumping UV or VUV radiation in active media is suggested and experimentally verified. This model explains both the presence of color centers of electronic and hole nature in crystals activated by cerium and the mechanism of suppressing of solarization processes after additional activation of the samples by Yb3+ ions. The cross sections of the processes of free-carrier capture by various ytterbium impurity centers are estimated. These impurity centers are established to be effective centers of recombination of free carriers of both signs. 相似文献
19.
Coupled-channels calculations for the elastic and inelastic scattering of K+ at 715 MeV/c by 6Li and 12C at 635, 715 and 800 kaon Lab momenta have been analysed. The optical potentials of 12C and 6Li are calculated in terms of the alpha-particle and deuteron optical potentials. Good fits to the experimental data and phenomenological
calculations are obtained for 6Li and 12C nuclei. 相似文献
20.
Shen Shuifa Fang Keming Gu Jiahui Liu Qingcheng Xu Furong 《The European Physical Journal A - Hadrons and Nuclei》2007,32(2):149-158
The decay of 95Ru has been investigated by means of γ-ray spectroscopy. The 95Ru nuclei were produced by the reaction 92Mo( α, n) 95Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of 95Ru to 95Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of 95Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed
from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus 95Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of 95Tc is discussed in the framework of the projected shell model. 相似文献