摘要:

A departure from stoichiometry is known to affect transport properties in oxides. Thus at temperatures where the formation is diffusion controlled, it is also affected by stoichiometry. To illustrate this point, a series of experiments on a variety of oxides is described. However, accurate interpretation of the results requires a detailed understanding of the dislocation core structures in oxides and how these structures can be influenced by a deviation from stoichiometry.

ISSN:0033-7579    

DOI:10.1080/00337578308218397

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Recent experimental and theoretical studies of the nature of transport and disorder in the high-temperature fiuorite-structured halides is reviewed. The bulk of the information suggests that the anion motion in these systems consists of discrete jumps rather than a cooperative liquid-like diffusion. Although it is now clear that anions do not appreciably occupy the cube-centre interstitial sites the exact extent of the disorder has still to be resolved.

ISSN:0033-7579    

DOI:10.1080/00337578308218398

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

From diffusion measurements in readily classified “stoichiometric” or “non-stoichiometric” cubic oxides we have deduced formation and migration enthalpies of point defects.

ISSN:0033-7579    

DOI:10.1080/00337578308218399

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Irradiation of ionic crystals causes the displacement of lattice ions and the formation of primary defects in the form of vacancies and interstitials. At high temperatures when these defects are mobile secondary defect reactions will produce various types of defect clusters. In some compounds clustering can lead to the formation of small particles of the metal constituent, referred to as colloids. A well-known example of this effect occurs in the alkali halides, where the colloids form as the result of large-scale aggregation of the primary F centres, so that the metallic region in this case derives from primary defects on the anion sublattice. The latent image of the photographic process in silver halides is also an example of the formation of a small metal colloid, and other crystals such as hydrides and azides can also be partially decomposed into metallic particles by irradiation with ionizing radiation. Recently metal colloids have been found as a result of displacement damage in the oxides Li2and Al2O3. This article reviews some of the background properties of colloids in ionic crystals and describes some examples of colloid formation by irradiation. Colloid growth in NaCl is described in more detail, since recent experimental and theoretical work provides a more complete picture than in other compounds. The Jain-Lidiard theory explains many features of the behaviour observed during high dose irradiation at high temperatures, and some comments are made about ways in which the theory could be developed further.

ISSN:0033-7579    

DOI:10.1080/00337578308218400

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Radiation induced processes in crystalline and amorphous solids are discussed. The primary act of ionizing radiation is similar in both materials. The majority of secondary radiation stimulated processes in crystalline and amorphous solids are similar, too. Differences may occur in focusing collisions and channelling processes where the interaction takes place in the host lattice. Besides, the present paper is concerned with the study of recent developments in radiation damage in solids (radiation colloids, swelling effects).

ISSN:0033-7579    

DOI:10.1080/00337578308218401

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A review is presented of the high temperature plastic deformation of sapphire (single crystal α-Al2O3), both undoped and doped with isovalent and aliovalent cations. The dislocation substructure in deformed samples is related to three different regions of the stress-strain curve and permits understanding of both work hardening and recovery.

ISSN:0033-7579    

DOI:10.1080/00337578308218402

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The paper summarizes the present situation concerning the measurement and interpretation of the thermopower in ionic crystals. We begin by recalling the physical origin of the thermopower and by showing how it can be phenomenologically expressed in terms of the heats of transport of the lattice defects. The heat of transport gives a measure of the thermodynamic force exerted on a defect by a temperature gradient; according to the Onsager reciprocal relations they also measure the heat flux which accompanies the diffusion of defects in the absence of a temperature gradient. We then review the experimental method of measuring thermopowers, noting that the measured quantity is a sum of two parts; the so-called homogeneous and heterogeneous contributions; it is the former which contains information about the heats of transport. Next, we turn to the question of atomistic interpretation. We show that simple physical ideas can give a rough estimate of the magnitude of the heats of transport, but that they are incapable of giving an adequate explanation of the experimental results. This leads to a brief description of recent theoretical progress, which indicates that it is fruitful to relate the heat of transport to the atomistic heat flux associated with the elementary jump process of a defect. We show that the calculation of this heat flux by computer simulation allows one, in principle, to obtain theoretical results for the heats of transport. We conclude by mentioning some preliminary steps which have been taken towards implementing such a claculation for vacancies and interstitials in fluorite crystals.

ISSN:0033-7579    

DOI:10.1080/00337578308218403

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The clustering kinetics and the nature of the early precipitation products in alkali and silver halides doped with divalent cations are reviewed. The dissolution and nucleation kinetics in the same materials are shortly discussed. The experimental results and theories which stress the clustering phenomena in fluorite-like crystals are reported as well.

ISSN:0033-7579    

DOI:10.1080/00337578308218404

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

All quartz contains Al3+ions substituting for Si4+ions with an adjacent interstitial alkali or a proton providing the necessary charge compensation. When thermally released from their trapping sites the interstitials can migrate along the relatively large c-axis channels. Li+is the predominant charge compensator in commercially grown quartz. If the sample is heated with an electric field applied along thec-axis the alkalis will be swept out and released either by protons or by another alkali. This electro-diffusion or sweeping process can be used to selectively dope the Al3+site. Applied fields of approximately 15 V/cm and 3000 V/cm result in equivalent current densities for alkali ions and hydrogen respectively. Alkalis show activation energies between 0.95 and 1.4 eV; hydrogen shows an activation energy near 1.9 eV. If ionizing radiation is present, hydrogen is mobile at all temperatures; however, the alkalis only become mobile at temperatures above 200 K. A comparison of the radiation induced mobility of sodium and lithium electro-diffused samples shows that sodium becomes mobile under irradiation approximately 10 to 15 K higher than lithium.

ISSN:0033-7579    

DOI:10.1080/00337578308218405

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Radiation effects in synthetic and high purity synthetic quartz are examined in a research programme at the GEC Hirst Research Centre concerned with the growth of high purity synthetic quartz and the development of radiation hardened quartz devices.

ISSN:0033-7579    

DOI:10.1080/00337578308218406

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor