摘要:

The electronic bands of aLiB3O5(LBO) crystal with excellent nonlinear optical properties have been studied using the scattered-wave method in embedded-cluster model. Calculations were carried out for a [B3O7]5−cluster, as this anionic group is the crystal basic structural unit. The interpretation of experimental photoemission spectra is based on electronic structure cluster calculations. From calculation performed, it follows that the contribution of trigonal and tetrahedral boron-oxygen groups dominates in the electronic structure of LBO, the contribution of 2p-boron states is immaterial.

ISSN:1042-0150    

DOI:10.1080/10420159508227185

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electron structure of the oxygen vacancy in SrTiO3has been computed for the first time in frames of the approach that does not use a basis. The SCF Xα SW technique is used for this purpose. The clusters considered have 4 coordination spheres included. A satisfactory agreement with experiment is obtained for the cluster modeling the ideal crystal.

ISSN:1042-0150    

DOI:10.1080/10420159508227186

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An excitation transfer among carbon-oxygen and vacancy-oxygen defects in electron irradiated silicon was studied by means of the photo-Electron Spin Echo (photo-ESE) technique. Analysis of the appropriate rate equations enabled us to estimate quantum yield of nonradiative tunneling among (C-O) and (V-O) centers. These processes were found to be several orders of magnitude more efficient than donor-acceptor pair radiative recombination and bound exciton radiative transitions.

ISSN:1042-0150    

DOI:10.1080/10420159508227187

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper focus on theory of diffusion-controlled annealing of the most mobile radiation-induced defects—I centers—in KCl crystals. The kinetics of annealing of pairs of close oppositely charged defects—α-I centers (arising as a result of the tunnelling recombination of primary Frenkel defects—F and H centers) and F-I centers (when H center trap electrons) is calculated taking into account defect diffusion and Coulomb/elastic interaction. Special attention is paid to the conditions under which multi-stage annealing arises; theoretical results are compared with the relevant experimental data.

ISSN:1042-0150    

DOI:10.1080/10420159508227188

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The semiempirical method of the Intermediate Neglect of Differential Overlap (INDO), in the program SYMSYM, has been used for calculations on perfect and imperfect corundum crystals. For the perfect crystal the periodical Large Unit Cell (LUC) model was used while the Molecular Cluster (MC) model was used in defect calculations. By means of the MC model, we have investigated the optical properties of electronic centers (F+, F, F−, FMg, F−Mg) in corundum. Calculated optical properties of these defects are compared with experimental values and new bands are predicted to exist in the absorption spectrum of Mg-doped corundum. The energy levels of F-type and Mg-impurity related centers are found to lie in the gap between the upper valence band and conduction band, as for similar centers in MgO and alkali halides.

ISSN:1042-0150    

DOI:10.1080/10420159508227189

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Atomistic computer modelling and Extended X-ray Absorption Fine Structure (EXAFS) measurements were used in a study of the mode of solution of Sr2+ions in La2O3. The results are in agreement with previous modeling studies which show that the most favourable mode of solution is cation substitution with anion vacancy charge compensation. The energy of solution was found to be 1.3 eV. The Sr K-edge EXAFS results for 10 and 20 mole percent Sr2+doped La2O3were consistent with cation substitution. For both doped samples the EXAFS indicate the presence of a defect cluster containing 2SrLaions adjacent to a Vo.

ISSN:1042-0150    

DOI:10.1080/10420159508227190

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electronic structure of [CsCln] molecular cluster and possible radiative transitions between crystal valence band and impurity core states are calculated with self-consistent field Xαscattering wave method. Correlation of experimental and theoretical data confirms the local cluster-type nature of the radiative core-valence transitions.

ISSN:1042-0150    

DOI:10.1080/10420159508227191

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We report the first general calculation of the empirical parameters appearing in the Mollwo-Ivey relation between absorption energy and interionic spacing for defects in ionic solids. The calculation is based on the Vinti sum-rule formulation of the Mollwo-Ivey law [Phys. Rev. Lett.69, 184 (1992)], a self-consistent Hartree-Fock-Slater procedure for defect ions, and a host-crystal environment modeled in the point-ion approximation. The Ivey exponent is reproduced in most cases to within better than 20% using this model in the alkali halides. The wide range of Ivey exponents can be qualitatively understood in terms of the compressibility of the defect.

ISSN:1042-0150    

DOI:10.1080/10420159508227192

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It is known that high ionic conductivity in fluorite-structured materials is associated with thermally created Frenkel-type disorder at temperatures well-below the melting point. Using crystallineLi2Oas a model system, we studied the mechanism of formation of Frenkel pairs at temperatures close to the transition to the fast-ionic phase, and ionic motion at temperatures above the transition point. The dynamical behaviour of lithium oxide has been studied using both lattice dynamics within the quasi-harmonic (QH) approximation and molecular dynamics (MD).

ISSN:1042-0150    

DOI:10.1080/10420159508227193

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The reliability of the lattice simulations depends on the quality of the potentials used. Hence, the interionic potentials of CdF2were derived and used in the calculations of the crystal bulk data. The temperature dependences of elastic constants is investigated. Elastic properties are predicted. The complementary studies using Brillouin scattering methods, show that the disorder at the transition temperature (Tc≊ 900 K) results in an abrupt decrease in the elastic constant C11. Both methods show that the elastic constants linearly decrease with increasing temperature within the low temperature region. Similar trends have been observed in other fluorites. This shows that our interionic potentials reproduce the behaviour of CdF2reasonably well.

ISSN:1042-0150    

DOI:10.1080/10420159508227194

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor