摘要:

In this brief review recent progress in the application of computer simulation techniques to the thermodynamics and diffusion processes in highly nonstoichiometric materials is discussed. For the discussion of thermodynamics we review the application of the Monte Carlo method and its recent full integration with lattice relaxation methods. For the discussion of diffusion we also review the application of the Monte Carlo method with special emphasis on concentrated as well as defective systems and also its integration with lattice relaxation methods. Testing of relations among phenomenological coefficients, tracer diffusivities and ionic conductivities is also commented on.

ISSN:1042-0150    

DOI:10.1080/10420159508227175

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The absence of long range order in the glass structure allows to define only point defects in these materials. They are: 1) intrinsic defects—atomic size local deviation from short range order; 2) impurity defects—isolated impurity atoms or ions in the glass network; 3) intrinsic impurity defects—complexes consisting of the impurity atoms chemically bonded to one of the intrinsic defect atoms. The latter defects are characteristic for the doped glasses. Presence of point defects in glasses introduces new spectroscopic properties of these solid materials. Defect generation, interaction and recombination reactions resulting from the external influence causes the glass spectroscopic property changes.

ISSN:1042-0150    

DOI:10.1080/10420159508227176

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Process of diffusion controlled phase decomposition of oversaturated solid solution, which makes it possible to grow semiconductor nanocrystals in a glass matrix and to vary the size of them in a controlled manner, is reviewed. It is demonstrated that optical properties of semiconductor-doped glasses are governed by quantum confinement of electronic and vibronic excitations in the nanocrystals. Manifestations of the quantum size effect in absorption, luminescence and Raman scattering spectra of these composite materials are regarded.

ISSN:1042-0150    

DOI:10.1080/10420159508227177

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Scintillator materials are widely used for the detection of ionizing radiation in a variety of applications including high energy and nuclear physics, astrophysics, geophysical exploration, medical imaging, security inspection, and industry. Research involving the use of photoluminescence, radioluminescence, thermoluminescence, and synchrotron radiation is underway to further our fundamental understanding of the factors affecting scintillator performance and to discover improved materials. The importance of defects and their effects on energy transfer and overall scintillation efficiency are illustrated by considering recent results for cerium-activated crystals and glasses.

ISSN:1042-0150    

DOI:10.1080/10420159508227178

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The sol-gel method is firstly described taking the TiO2-SiO2system as an example of the chemical procedure and its effect on the structure of the obtained material. The possibilities given by this low temperature synthesis are briefly described giving particular emphasis on so-called hybrid materials. The second part of the paper is devoted to defects in sol-gel materials. Studies on Raman active defects and paramagnetic states are reviewed. A brief discussion on crystallization defects is also presented.

ISSN:1042-0150    

DOI:10.1080/10420159508227179

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The intrinsic luminescence quenching of the F center in NaI and NaBr has been the subject of discussion for many years. The key question was whether the nonradiative electronic transition to the ground state after optical excitation occurs during or after lattice relaxation in the excited electronic state. Ultrafast time resolved techniques showed that in the case of NaBr the electronic transition predominantly occurs from the relaxed excited state (RES), whereas in NaI the electronic transitions during and after lattice relaxation have a comparable efficiency. A similar question raises when the luminescence is quenched by aggregation of theF-center with a molecular impurity. In addition one wants to characterize the electronic-vibrational (e-v) energy transfer associated with the nonradiative F-center relaxation by measuring the population of the vibrational levels after the transfer. Ultrafast spectroscopy can contribute to a better understanding of the e-v transfer process in particular in the case of the OH−perturbedFcenter: Because of the stronger quenching of electronic luminescence and the much faster (nonradiative) vibrational decay for OH−, much fewer information is available yet than in the case of CN−.

ISSN:1042-0150    

DOI:10.1080/10420159508227180

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Quantum-mechanical calculations and atomistic simulations have been used to characterize the local geometry, stability and resonant vibrations of CuAcenters in alkali halides

ISSN:1042-0150    

DOI:10.1080/10420159508227181

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper describes the calculations of the electronic structures of the F-center in NaCl, pure anion vacancy. F+andF-centers in MgO by the embedded cluster method. This work is an alternative approach relative to the ICECAP method within which the embedded cluster model based on Johnson's Scattered Wave method is combined with the Mott-Littleton method. The main features of the model are: self-interaction correction of single-particle energies in the case of perfect crystals and point defects whose states are in the band gap of a perfect crystal: Mott-Littleton method modification allowing for the description of the defect wave function in the analytical form: construction of the cluster one-electron potential when describing the rest of the crystal in shell model terms.

ISSN:1042-0150    

DOI:10.1080/10420159508227182

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We discuss the nature of the defects involved in the incorporation of hydrogen in oxides and silicates. We describe how computational techniques may be used to investige the structures and energies of hydrogen containing defects in these materials.

ISSN:1042-0150    

DOI:10.1080/10420159508227183

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A2BX4single crystals (A = Cs, Rb, N(CH3)4; B = Cd, Zn, Mn, Fe; X = C1, Br, I) with β−K2SO4type structure belong to the compounds with the different phase transitions (PT), including PT into incommensurate structure. The persistence of the transitions metals play an important role in the investigations of PT by the ligands field in the types of crystals, in particular, in the vicinity of phase transition. The nature of the corresponding phase transitions is closely connected with the tetrahedral complexes [B2+X4]2−bounded by A−cations. The Mn2+ions were chosen due ithe persistence of the five external d-electrons, which are highly sensitive to the external fields. The present work deal with experimental and theoretical investigation of the electronic band structure and optical parameters of [N(CH3)4]2MnCl4and Cs2CdI4single crystals.

ISSN:1042-0150    

DOI:10.1080/10420159508227184

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor